Wednesday, July 31, 2013

Heat Continues, Isolated T-Storms

By Jay Grymes & Steve Caparotta

As we’ve seen the last few days, pockets of showers and storms developed during the afternoon, with the main action occurring over the southern parishes.  For most of us, however, it was just another in a string of hot-and-humid days.

We’re staying with a “very hot and mostly dry” forecast for the rest of the week and right through the weekend - - look for daily rain chances at 20% or less through Sunday, with morning lows in the mid to even the upper 70°s around metro Baton Rouge and afternoon highs in the low to mid 90°s.  Factor in our summer humidity and the afternoon Heat Index readings will likely peak out in the triple-digits -- so be extra careful in the heat, especially if you are not accustomed to it.

The upper-level ridge over the Southern Plains will remain a dominant feature in our weather for the next several days, providing a bit of a lid on the local atmosphere.  That lid inhibits the vertical development of the afternoon clouds -- that means not only less rain but also more sunshine to drive the afternoon temperatures up.

With the build-up of heat through the day coupled with dew points running in the low to mid 70°s, it not only gets uncomfortably hot in the afternoon but the cool-down is slow to set-in through the evening and even into the overnight.  As a result, we’ll have more muggy morning starts to deal with right into next week.

A weak cool front will try to make its way into south Louisiana during the next day or so.  However, we don’t think it will do much in terms of impacting the expected heat, nor will it do much in terms of promoting local rains.  By the weekend, the boundary will have lifted north as a warm front, leaving us with our humid Gulf air.

Elsewhere ... all quiet in the tropics: no tropical waves in the basin are displaying any serious potential for development over the coming days.

Tuesday, July 30, 2013

Closing Out July Hot & Humid

By Jay Grymes & Steve Caparotta

At 3PM, Titan9 Doppler was showing some showers and a few t-storms over Washington and St. Tammany parishes as well as a few spots of rain over the southern parishes of the WAFB viewing area.  In general, our forecast for this afternoon held true: spotty showers in the viewing area with afternoon highs in the low to mid 90°s.
Get used to it.
Our forecast for Wednesday and Thursday reads like a repeat of today: morning lows in the mid 70°s, afternoon highs in the low to mid 90°s with spotty t-showers.  Most of us will stay dry over the next several days, with muggy morning starts and hot afternoons.
Yesterday we mentioned the southward advance of an upper-level trough over the eastern U.S. towards the end of the work week.  While we still expect the trough to materialize, it now looks like it might not be quite as vigorous of a surge as we initially thought.  That means its influence over the Southern Plains upper-air ridge -- which is the feature keeping us hot and mostly-dry right now -- won’t be quite as effective.  In other words, we don’t think the ridge will contract as far to the west as we thought yesterday.

The less the ridge shifts west, the greater its influence remains.  On Monday we thought we would see rain chances increase to the “scattered” category by Friday (up to around 30% or so) -- now, that doesn’t appear as likely.
For today, we’re going with “isolated” afternoon and early evening rains for Friday and right through the weekend.  We’ll keep those percentages at 20% for early next week, but that may be a bit generous -- the southern ridge may rebuild back to the east by next week, recreating a “lid” on the atmosphere and really limiting the rain potential to something closer to “spotty.”

Over the past few weeks, some WAFB communities neighborhoods have seen some big rains.  For example, this past Saturday we had reports of some neighborhoods in and around Central, Watson and northern Denham Springs getting as much as 3” to more than 5” of rain with the passing storms.  But many WAFB neighborhoods -- especially farther to the east and southeast of the greater metro Baton Rouge -- are running a bit on the “dry” side for the month.
While there is no impending drought threat in our viewing area just yet, southern and central parishes to the west of the Atchafalaya basin have been rated as “Abnormally Dry” for this time of year by the U.S. Drought Monitor.  Our forecast for the coming seven days certainly doesn’t signal any immediate relief.
In the tropics, dry air and an upper-level low just to the west of Dorian’s remnants have continued to pound the tropical wave even further today.  As a result, the National Hurricane Center at 2PM issued an outlook with “near 0% chance” of Dorian’s remnants re-developing into a tropical cyclone over the next 48 hours.  However, given that the wave still may be headed into the southeastern Gulf, we’ll keep a watch on it for you.

Monday, July 29, 2013

Hot, Isolated Rains Next Couple of Days

By Jay Grymes & Steve Caparotta

We’ve been watching spotty to isolated showers, with a few t-storms, developing along a “broken” convergence line extending from Wilkinson County southward into the coastal marshes of Terrebonne Parish.  The line hasn’t moved much, and most of the pop-up showers along the convergence zone have been short-lived, but a few have developed into stronger t-storms over lower Terrebonne.
We expect most, if not all, of the shower activity to be gone by sunset, with skies becoming mainly fair later tonight and staying that way into Tuesday morning.  We’ll open Tuesday with sunrise lows in the low 70°s for the greater BR metro area.
For Tuesday afternoon, we expect essentially a repeat of today: partly cloudy skies with afternoon rain coverage of less than 20% for the WAFB viewing area.  Highs will reach the low to mid 90°s.
Our forecast for Wednesday and Thursday are not much different either: morning lows in the low to mid 70°s, afternoon highs in the low to mid 90°s, and afternoon rain chances running at about 20%.  In the extended, we’re posting a 30% rain chance for Friday, then back down to 20% for both Saturday and Sunday.  In effect, our forecast through the work week and weekend calls for near-normal lows, slightly above-normal highs, and slightly-below-normal rain chances.

A frontal boundary to our north will not make it much farther south, keeping us under the influence of our summer-season warm-and-moist Gulf air mass.  At the mid and upper levels, ridging centered over Texas extends westward into Louisiana, serving as a weak lid on the atmosphere that limits vertical development of clouds for afternoon showers even with the “unstable” air mass in place.
Based on what we’re seeing right now, an upper-level trough will dig southward over the eastern U.S. by mid-week, putting the squeeze on the Texas ridge and nudging the ridge to the west.  That should allow for a very slight increase in rain chances for possibly Thursday and especially Friday.  But the upper trough is expected to lift out to the northeast for the weekend, allowing the Texas ridge to re-expand towards Louisiana and keeping weekend rain chances in the “isolated” category for Saturday and Sunday.
And in the tropics, the remnants of Dorian are readily apparent to the north of Puerto Rico, but the satellite imagery also shows that dry air and an upper-level low to the west of the remaining convection continue to take their toll on the remnants.  There is still no “closed low” at the surface nor does there appear to be much chance for one to develop in the near-term.  These factors -- along with the fact that some of the more trustworthy models fail to call for Dorian’s “re-birth” -- are likely to be key reasons why the NHC has dropped their re-development potential to 30% (through the next 48 hours) as of this afternoon. 

Elsewhere, there are no other Atlantic Basin tropical waves displaying any immediate threats for development at this time.

Friday, July 26, 2013

Mixed 'Weather Bag' this weekend
This morning’s low of 69° for Metro Airport was the first time the airport dipped below 70° since the morning of July 13th. If you are one of those early-morning commuters, runners or walkers, you probably noticed that the air was a tad cooler and less humid.
Even with the day’s mild start, the heat returned for the afternoon. However, once again the forecasts for mid 90°s were a little too high, although just about everyone saw temps climb into the low 90°s. With dew points ranging from the upper 60°s to low 70°s for most WAFB neighborhoods, at least the mid-day heat was tolerable, especially for late July.
The recent run of “mainly dry” days comes to an end, if only briefly. A cool front currently to our north and northwest -- linked to a surface low over the Southern Plains -- will continue to move in our direction tonight and tomorrow. As the surface low slides east, a trailing cool front should move into the WAFB viewing area on Saturday afternoon, hoisting rain chances into the “likely” category and accompanied by scattered t-storms. Not everyone will get a soaking, and we don’t expect an all-day rain event, but rain coverage should be fairly widespread -- we’re calling for a 60% chance of rain for your backyard.
While we can’t rule out a few strong storms as the front pushes through, the good news is that we are not anticipating a severe-weather outbreak with the frontal passage. Saturday’s rains should also mean a break from the 90°s for many WAFB communities.
We had expected Sunday to also be another day with scattered afternoon t-showers, but our latest guidance is backing off on the higher rain chances. Our forecast for Sunday now calls for only isolated afternoon rains, with highs climbing for most of us back into the low 90°s.
In the extended outlook, our forecast calls for isolated afternoon showers, at best, for most or all of the work week. Plan on lows in the low to mid 70°s with highs back into the low 90°s each day..
So ... what about Dorian?
T.S. Dorian has been struggling a bit over the last day. After reaching peak sustained winds of 60 mph yesterday, Dorian has weakened a tad and the latest forecast from the National Hurricane Center (NHC) calls for additional weakening in the coming days. In fact, the NHC’s 4PM Advisory calls for Dorian to drop to depression strength within the next couple of days and then “dissipates” Dorian by next Wednesday.
We admit that the NHC’s forecast for the demise of Dorian comes as a bit of a surprise, but clearly Dorian is headed into a region of a more hostile wind shear.
Dorian has maintained a west-northwest trajectory since becoming a tropical storm in the eastern Atlantic and the forecast for the next few days shows that general trend continuing through the weekend and into next week even while the system struggles to survive. In fact, the latest forecast suggests a path that is almost “due west” as the system approaches the Caribbean island chains.
But here’s the key: even if Dorian survives through the next five days, it’s likely that the system will still be roughly 500 miles east of the Gulf of Mexico and likely more than 1000 miles from coastal Louisiana in the middle of next week. So let’s not start getting too concerned about Dorian just yet.
However, this weekend would be a good time to review your “family hurricane plan” and make sure that you are stocked and ready-to-go.

Thursday, July 25, 2013

Better Rain Chances by Saturday

The same weak trough of low pressure that delivered some late-day rains to parts of the area on Wednesday helped spark some early showers and t-storms in our coastal parishes today. Most of that activity shifted offshore by late morning and left behind a mainly dry afternoon for the WAFB viewing area.

Once again today, temperatures have fallen short of forecast readings (I don’t think anyone is complaining!). In fact, highs have only topped out near or slightly above 90° for most, even though we were expecting mid 90°s. Leftover clouds from the morning rains along the coast were at least partially responsible for the lower-than-expected temps.

Our computer guidance is once again forecasting highs in the mid 90°s for Friday, but we have to be somewhat skeptical since the guidance has run above reality just about all week. The 2 models we look at most closely on a daily basis are both forecasting a high of 96° for Baton Rouge on Friday. Given this week’s trends, we’ll undercut that by a couple of degrees and go with 94° and even that could be a reach.

Rain chances stay low on Friday, but a much better chance of showers and t-storms is expected by Saturday. A weak cool front approaching from the north, combined with an upper-air disturbance will lead to at least a 50% chance of showers and t-storms. The clouds and associated rains should keep highs close to 90° for most.

The big question for Sunday’s forecast relates to where the weak cool front eventually stalls. If it makes it to the coast, somewhat drier air would result in lower rain chances. If it stalls near or just north of us, scattered showers and t-storms would remain. For now, we’ll go with a 30% chance of showers and t-storms for the second half of the weekend.

Fairly typical late-July/early-August weather is expected into next week, with hot and humid afternoons and a slight chance of showers and t-storms each day. If anything, rain chances may run a bit below-normal next week.

And we continue to track Tropical Storm Dorian as it makes its way through the Atlantic. After struggling a little bit with slightly cooler water temperatures earlier today, the storm seemed to rebound this afternoon. Maximum winds were still listed at 60 mph as of 4 PM. The official forecast track hasn't really changed much and still has Dorian moving just north of the Lesser Antilles over the weekend before possibly approaching the Bahamas early next week.

We're already getting many 'Is it coming here?' questions. The short answer is it's just too soon to say. Even if it did make it to the Gulf -- and that's a big 'IF' -- it's still probably about a week away from doing so. I did take a look at historical storm tracks this afternoon and the results might surprise you. Since 1850, only 2 tropical systems passing within 150 miles of Dorian's current location made it into the Gulf. That's out of more than 80 depressions, storms and hurricanes during that stretch. The two that did make it to the Gulf included a 1915 hurricane that made landfall near Galveston and 2008's Hurricane Ike. Does that mean Dorian won't make it to the Gulf? Not necessarily. But history tells us the odds are relatively low. Let's hope they hold!

Wednesday, July 24, 2013

Hot, Isolated Storms Next Couple of Days

By Jay Grymes & Steve Caparotta

Today was another hot one, but afternoon breezes with occasional gusts into the 20s made the heat almost tolerable by summer standards.  In addition, a fairly persistent cloud deck through much of the day filtered the sunshine and helped slow the daytime temperature rise.  Indeed, most of the viewing area didn’t see the mid 90°s we had expected, thanks largely to the wind and clouds.

Upper-level ridging remains in charge to our west, centered over New Mexico.  While the ridging is keeping us mainly-dry and hot, we’ll continue to keep an eye on the stormy disturbances traveling along in the NW-to-SE upper-level flow.  Yesterday was saw some big t-storms rolling through Mississippi and Alabama in this flow ... and last night we watched storms move from Arkansas into northern Louisiana as the upper-level flow eased slightly westward and closer to us.

This afternoon we are watching yet another disturbance slide into central Louisiana from the northwest.  While we think most of the energy in this cluster will weaken before getting this far south, a few WAFB neighborhoods could get a shower and just about all of us will see some clouds as what’s left of this disturbance passes by.

And tomorrow?  Much the same as today.  We’ll start off in the mid 70°s around the ‘Red Stick,’ under partly cloudy skies with maybe a shower or two in the early morning (mainly closer to the coast).  Temps will be pushing the upper 80°s to near 90° by the lunch hour with afternoon highs for many metro area neighborhoods approaching the mid 90°s.  We’ll go with isolated to spotty showers for Thursday afternoon -- setting rain chances at 20% or less.

Plan on a repeat of Thursday’s forecast for Friday.

Into the weekend, the upper-level ridging breaks down over the region and a weak cool front looks like it will stall to our north.  That will allow a return flow set-up with moist Gulf air adding to the instability and prompting better rain chances for both Saturday and Sunday.  “How wet?” remains under a bit of debate, but the rain should help the lawns and break the mid-90°s heat.

Elsewhere ... the tropics are getting more active.  There is a new “invest” (an ‘area of interest’) in the west-central Atlantic labeled 99L (or AL99), but the early models suggest that whatever comes of it stays out over the ocean.

Of more interest to us is T.S. Dorian, located in the far eastern Atlantic.  As you may recall, we were talking about 98L last night, noting that the satellite view showed some signs that 98L was ready for an “upgrade.”  The NHC “upped” 98L to Tropical Depression #4 at 5AM this morning, then “upped” it again at 10AM to the season’s fourth named storm: Tropical Storm Dorian.

Dorian is way too far out for us to get concerned about at this stage, even though the 5-day NHC forecast -- and almost all of the reliable computer models -- keep Dorian on a track pointed towards the Gulf.  But even if this forecast is spot-on, as of this weekend Dorian will still be well to the east of Cuba.  In addition, while the models are currently showing pretty good agreement through the next 5 days, they really start to diverge after that.

So let’s just sit back and see what happens.  There is plenty of time before we need to start thinking about this storm ... assuming, of course, that you have done your pre-season prep already.

Tuesday, July 23, 2013

Staying Hot, Mainly Dry on Wednesday

By Jay Grymes & Steve Caparotta

Tuesday started out warmer-than-normal for the early morning and rather muggy as well. And, as we expected, it stayed dry and on the ‘hot’ side through the afternoon.

A look at the regional radar this afternoon showed a T-Storm Watch extending over central sections of Mississippi and Alabama -- along with a large convective complex (t-storm cluster) traveling from NW to SE through the Watch ‘box.’ Those storms were riding with the flow along the eastern flank of a building upper-air ridge -- the same ridge that will keep us hot-and-mainly-dry for the next couple of days, at least.

A cool front will be slowly sagging southward across the eastern third of the country through the middle and end of the work week. The latest guidance suggests that the front will reach the Arkansas/Louisiana border by early Thursday and might make it as far south as the WAFB viewing area by Friday. But the current thinking is that the front will stall rather than push through the viewing area and begin a northward retreat late Friday or early Saturday. The result: the front will provide little relief from the heat and Gulf humidity as we head into the weekend.

So let’s plan on mostly-dry days right through Saturday. 

We’ll call for Wednesday to be essentially a repeat of today, with spotty showers, at best, in the afternoon. For Thursday, we’ll go with rain chances at 20% or less and only a 20% chance for afternoon showers on both Friday and Saturday. Morning lows into the weekend will be in the low to mid 70°s for metro Baton Rouge with afternoon highs in the low to mid 90°s.

We could get some minor relief from the heat on Sunday, with rain chances currently expected in the 30% to 40% range. After that, it looks like we’ll return to isolated afternoon showers for the early part of the next work week.

The far-eastern Atlantic tropical wave that we pointed out yesterday -- 98L, also known as AL98 -- is looking even better on satellite today, prompting the National Hurricane Center (NHC) to “up” their potential to 60% for AL98 to become a tropical cyclone (tropical depression or tropical storm) within the next 48 hours. Most of the models support development over the next couple of days -- at the same time, they also keep the system moving generally to the west.

But let’s not spend too much time on AL98 right now: even if it does develop, it’s five or more days east of the Lesser Antilles!

Monday, July 22, 2013

By Jay Grymes & Steve Caparotta

Although there were still some pockets of showers and t-storms moving west-to-east across the Florida Parishes as of 4PM, most of the day’s more widespread rains rolled through the viewing a little earlier in the day.  Those earlier rains took a good deal of punch out of the unstable atmosphere but a serious deck of clouds persist for many communities, filtering much of the late afternoon sunshine.  As a result, the typical afternoon climb into the 90°s was slowed a great deal -- in fact, most WAFB neighborhoods topped out in the 80°s for their afternoon highs.
Don’t be expecting a repeat performance any time soon!
Upper-level ridging currently extending over most of the western U.S. will expand eastward for the next several days; at the same time, high pressure will build over the Gulf.  These two features point to a noticeably drier and hotter forecast, with afternoon highs for many WAFB neighborhoods climbing into the mid 90°s for the next few days, at least.  Based on our current forecast, we’re heading into what could well be the “hottest” week of the summer thus far.

The eastern extent of that upper ridge is expected to pull back to the west by late Thursday or Friday.  At the same time a cool front will try to make it down to the Gulf Coast -- but don’t count on it.  We think that the front will stall before getting here, then retreat back to the north.  However, with the upper ridge back to the west, we’ll increase rain chances as we head into the weekend, with the best chance for rain coming on Sunday.
It is really far too soon to be sure, but at least one extended range model hints that the western ridge will re-expand eastward early NEXT week, which could mean a return to warmer-and-drier days down the road -- we’ll see how that pans out in the coming days.

In the tropics, the NHC is watching an area of disturbed weather (Invest ‘AL98’) in the far eastern Atlantic -- just off the west coast of Africa -- and giving it a 30% chance for development into a tropical cyclone during the next two days.  While AL98 poses no threat to the U.S., Bahamas or Caribbean at this time, what is a little surprising is to see such a high probability for tropical cyclone development for a tropical wave so far east this early in the season.

Wondering about the sea-surface temps (SSTs) out ahead of AL98?
SSTs across most of the tropical Atlantic are a tad warmer-than-normal for this time of year and are warm enough to support storm development.  Admittedly, we’ll sit back and see what becomes of AL98 over the coming days, but let’s just hope that this is not a sign that the eastern tropical Atlantic is ready for action already!  It is way too early for ‘Cape Verde’ storms!

Friday, July 19, 2013

Keep An Umbrella Handy This Weekend

By Jay Grymes & Steve Caparotta

As expected, scattered showers and t-storms popped up across the WAFB viewing area as the afternoon sunshine combined with a moist air mass to do their typical summertime jobs.
Coverage today will remain in the 30% to 40% range for our viewing area before we lose the daytime heating later this evening.  We could see a rain pocket or two linger into the late evening, but all of the rain should be out of the area long before midnight.
We’ll start off Saturday morning mainly dry ... but clouds will build through the morning and into the afternoon.  We’re posting rain chances on the order of about 40% or so for Saturday afternoon with highs in the low 90°s.  We now think Sunday looks like the “wetter” of the two weekend days -- set Sunday’s rain chances at 50% to 60%.

A broad upper-level low over the central Gulf Coast region coupled with a broad surface trough over the northeast Gulf will make for some wet weather, but together they offer no real threat for tropical development over the coming days.  While the National Hurricane Center has posted the area with a “10% chance for tropical cyclone development over the next 48 hours,” the conditions just don’t seem at all favorable for anything to come of this.  It’s already too close to land, there is no indication of a surface low to be found anywhere, and the mid-level winds appear far too active to let anything build in the short time allowed.
As we head into next week, however, we’ll really turn the forecast around.
A well-developed upper-level ridge is expected to become established over the western U.S. by Tuesday and then expand eastward through the middle of the week.  With the lower Mississippi Valley positioned below the eastern flank of the upper ridge, we’ll be under the effects of “sinking air” from above.  That air warms as it descends -- a law of physics for the atmosphere -- adding to the heat-load at the surface.  But more importantly, that warm, descending air works against our traditional mid-day summer cloud development.  Fewer clouds means more solar energy reaching the ground -- and that means higher afternoon temperatures.

So by mid-week, our forecast keeps rain chances at 20% or less with afternoon highs reaching the mid 90°s.  Think sunscreen!
Metro Airport has hit 95° once this summer, on June 14th.  But get ready for what may be the “hottest” week of the summer if our forecast pans out.

Thursday, July 18, 2013

Scattered T-Storms into the Weekend

By Jay Grymes & Steve Caparotta

Showers and storms moved across the northern half of the WAFB viewing area during the morning and mid-day hours.  Those rains were courtesy of a southwest-bound outflow boundary that developed out of a thunderstorm cluster which had originated near the central Alabama/Mississippi border early in the morning.  Throughout the morning we watched as a band of storms tracked from NE to SW, reaching McComb at around 9AM, Hammond and Clinton close to 10AM, metro Baton Rouge, Gonzales and Reserve close to 11AM, and continued west and southwest into the mid-afternoon.

As of 3PM, most of the activity had subsided, with what was left of the storms located over  Acadiana.  That line of storms took much of the potential storm energy out of the atmosphere, leaving most WAFB communities with fair to partly cloudy skies and a less-humid air mass.  While a pop-up shower or storm remains possible through the late afternoon and early evening, most of us are done with the rains for today.

Skies will remain fair to partly cloudy overnight with sunrise temps on Friday in the low 70°s.  After a “dry” start to the day, the Storm Team forecast for Friday afternoon and early evening calls for a 30% to 40% chance of showers and t-storms but not before most neighborhoods see temps back in the 90°s.

The weekend shapes up much the same: mainly dry for Saturday and Sunday mornings with sun-up temps in the low 70°s, afternoon highs returning to the low 90°s, and scattered mainly afternoon and early evening showers and t-storms.  We’re setting rain chances for both days at about 40% or so.  A non-tropical area of low pressure in the eastern Gulf today will continue to move to the west and possibly northwest into the weekend, providing a little extra lift for afternoon rains for the already warm, moist and unstable Gulf air.

On the other hand, we’re adjusting our thinking regarding the forecast for next week.  Rather than a continuation of the “scattered rains” forecast that develops over the weekend, we are now getting some guidance that suggests a “drier” pattern over the central Gulf Coast, especially towards mid-week.

An upper-air ridge that is expected to build over the western U.S. this weekend is forecasted to expand eastward as the week progresses.  That should limit -- but not entirely block -- afternoon shower development over the central Gulf Coast by or before mid-week.  Of course, ridging also means “warming” and our forecast calls for highs in the mid 90°s while the rain chances fall into the “isolated” category.

And ... so far so good in the tropics.

Wednesday, July 17, 2013

Headed towards "normal" July weather
Looks like we got just about what we expected for today: a little less cloud cover and fewer showers which translated in a return to afternoon temps in the 90°s. Still there were some pockets of stronger t-storms during the afternoon across the WAFB viewing area -- a reminder that just because it is “quiet” over your backyard doesn’t mean that the weather is behaving throughout the viewing area!
The drier day also came with a slight drop in the mid-day and afternoon humidity, as dew points dropped a couple of degrees -- from the mid 70°s to the low 70°s -- into the afternoon. Unlike air temperature, a drop of just a few degrees in the dew point temperature can make a very noticeable difference in how “hot” the air feels.
Still, afternoon Heat Index values (HIs) climbed up to near the 100° mark for many WAFB neighborhoods. And don’t forget, direct sunshine from mid-morning into the mid-afternoon can add as much as 5° to 15° to the “apparent temperature” (what the heat ‘feels like’ to the skin).
We think we’ll have another mostly-dry day on Thursday as the dome of mid/upper-level high pressure (“ridging”) over the eastern U.S. continues to influence our area, keeping a modest cap on the development of afternoon rains. Let’s plan on rain chances in the 20% to 30% range for Thursday afternoon.
But by the latter half of Thursday and early Friday, the upper ridge will have begun to weaken and shift east. At the same time, it looks like a weak low pressure (non-tropical) over the Gulf could be approaching the central Gulf Coast. That should provide at least a modest increase in our rain chances for Friday and keep the weather “wetter” through the weekend.
At this point, we’ll go with scattered showers and t-storms for Friday, Saturday and Sunday -- setting rain chances at about 30% to 40% for Friday and then running about 40% for the weekend. And for the time being, we’ll keep rain chances running at about 40% for Monday through Wednesday too.
Does that seem too wet? Well, not really. In fact, that’s just about “normal” for July across WAFB Country.
To put it in perspective, long-term statistics for the metro area during July tell us that we record “measurable rainfall” (0.01” or more) an average of 12-13 days during July -- that works out to be roughly 40%. In fact, records from Metro Airport (BTR) show that there is a thunderstorm somewhere within view of BTR on half of all July days, although not all of those t-storms actually produce rain at the airport.
So get ready for a run of “average” July weather by the weekend: morning lows in the low to mid 70°s, afternoon highs in the low 90°s, and somebody somewhere getting some rain!

Tuesday, July 16, 2013

Drier Days Ahead

By Jay Grymes & Steve Caparotta

As expected, the “wet” pattern that we’ve seen the past couple of days continued today.  Scattered to occasionally numerous showers and t-storms moved from ESE to WNW through the afternoon, with Doppler radar estimates showing some isolated pockets of 1” to 2” of rain for the day.  A few of the day’s storms showed periods of very active lightning, but none reached ‘severe’ thresholds.
As we’ve seen each day, the rains will wind down as we lose daytime heating and we’ll go to partly cloudy skies later tonight with Tuesday sunrise temps in the low 70°s for metro Baton Rouge.
We expect a “drier” pattern for the next couple of days as mid/upper-level ridging extends over much of the eastern U.S., putting a damper on rain chances for Wednesday and Thursday.  We won’t say “no rain” for the two days but will post rain chances at about 20% across the WAFB viewing area for both afternoons.  Less rain and fewer clouds will mean a return to highs in the 90°s for both days, with one or two WAFB neighborhoods possibly reaching the mid 90°s.

By Friday, the upper ridge will be shifting to the east allowing for a return of better rain chances for Friday afternoon and the weekend.  We’ll post scattered afternoon and early evening showers and t-storms for all three days, with highs in the low 90°s for communities.
For now, at least, we don’t see any signals for much of a change in the pattern into early next week.  So we’ll keep scattered PM showers and t-storms in the forecast for next Monday and Tuesday as well -- rain chances that are typical for mid to late July.  Highs will stay in the low 90°s.

We’re watching an upper-level low and a surface trough in the Bay of Campeche -- neither offers any real threat for tropical cyclone development.  Elsewhere in the Atlantic Basin, it remains rather quiet.  You may be thinking, “Shouldn’t we be seeing more activity at this time of the Hurricane Season?”
To put it in perspective, although we haven’t seen anything significant in the tropics since last week’s Chantal, we are well-ahead of average in terms of ‘named’ storms for this time of the Hurricane Season.  According to the National Hurricane Center, on average, the third ‘named’ storm for the Atlantic Basin doesn’t appear until early/mid August -- in fact, the second ‘named’ storm, on average, doesn’t arrive until late July or early August.  Looking at it another way, on average, less than 20% of a season’s ‘named’ storms arrive before August 1st.
So, given the current state of affairs, it appears that we are still on-track for an above-average Hurricane Season this year.

Monday, July 15, 2013

More Rain on Tuesday

After a round of heavy rains for some on Sunday, showers and t-storms have been even a bit more numerous around the area today. While we haven’t seen any severe weather today, some of the storms have dumped 1 to 2 inches of rainfall in a short amount of time.

Our wet weather pattern is compliments of Gulf moisture surging inland between an upper-low to our west and high pressure centered off to our northeast. With that pattern expected to remain in place on Tuesday, look for another day of fairly widespread shower and t-storm activity. Many WAFB neighborhoods may not get out of the 80°s, but with a little sunshine, highs could easily hit 90° before any wet weather arrives.

The remainder of the week should be somewhat drier as the upper low moves farther away and high pressure builds in from the east. We’re not talking completely dry, but daily rain chances should run 20% to 30% each day from Wednesday into Friday.

Looking ahead, early indications are that we should see fairly typical summer weather for the weekend – scattered, mainly afternoon showers and t-storms, with highs in the lower 90°s.

And we’re happy to report that for now, the tropics remain quiet!

Friday, July 12, 2013

Warm, Less Humid on Saturday

By Jay Grymes & Steve Caparotta

Thankfully, today was quite the contrast to Thursday from a weather perspective in our viewing area.  While we are seeing a few showers and t-storms break out along a weak front draped over the state, those rains shouldn’t last long.  What’s more, it looks like we’ll stay that way through the weekend.
Today’s sunshine allowed the high at Metro Airport to top-out at 96° - - the highest reading thus far this summer!

The “cool” front we’ve been talking about for the past few days has arrived along the Gulf Coast and is going to do the job.  Now don’t be expecting truly cooler afternoons over the weekend … but you should notice at least a modest drop in our humidity levels for Saturday.  And here’s some added good news:  we think that the lower humidity levels will hang around for much of Sunday too.
Our Saturday forecast calls for a nice start to the day with sunrise temps near 70° for metro Baton Rouge -- in fact, some communities north and east of BR could even see some early morning 60°s.  Plan on lots of sunshine through the day, taking Saturday highs in to the 90°s -- a few WAFB neighborhoods will flirt with the mid-90°s on Saturday afternoon.  However, dew point temperatures in the 60°s will give the air a “dry” feel by July standards.  We can’t entirely rule out a rogue afternoon shower or two, but we’re posting Saturday rain chances at well under 20%, so just about everyone stays dry.
Probably the biggest change to our weekend outlook is our call for a mainly-dry Sunday.  Low-level moisture will be returning to the area on Sunday, but the increase in humidity will be slow enough to give us another “not bad” weekend day.  Sunday’s sunrise temps will be in the low 70°s -- a degree or two ‘warmer’ than Saturday’s morning lows -- with Sunday’s highs again in the low 90°s.  Set rain chances for Sunday afternoon at about 20% or so, still below July norms.
Our traditional Gulf humidity will have made a complete recovery by Monday – rainfall will jump back to a more typical July pattern of afternoon scattered showers and t-storms for the coming work week.  Morning lows will tend towards the low to mid 70°s with afternoon highs in the low 90°s just about every day through the week.

So what about what’s left of Chantal?  As we mentioned Thursday evening, there really isn’t much of a chance for Chantal’s remnants to make a comeback -- and that is good news in our opinion.  Although the National Hurricane Center (NHC) was calling for a 30% chance for a tropical cyclone to re-develop (within the next two days) last night, the satellite presentation suggested that 30% was awfully generous.  The NHC now has backed down to a 20% chance -- we think that is still generous -- and cancelled today’s planned flight for a Hurricane Hunter investigation.

As of this afternoon, what was Chantal now shows two distinct lobes of convection -- one just northeast of the northern Bahamas, the other on the south side of Cuba.  Neither looks threatening.  Elsewhere in the Atlantic Basin, we continue to track “easterly waves” coming off the Coast of Africa, but so far every one of these thunderstorm clusters has failed to develop upon reaching the open tropical Atlantic.  Great news, of course, but just remember, it’s still early in the season.
Enjoy our weekend!

Thursday, July 11, 2013

Less Rainfall on Friday

By Jay Grymes & Steve Caparotta

Most of you made it into the 90°s this afternoon before the showers and t-storms arrived.  The majority of this afternoon’s rains over the WAFB viewing area were the product of a persistent outflow boundary moving towards us all day long from the northeast.  The outflow was produced by a cluster of strong storms over Alabama and eastern Mississippi earlier in the day.

What is an “outflow boundary?”  Stated simply, an outflow boundary -- also known as a gust front -- is the leading edge of gusty, cooler air produced by thunderstorm downdrafts.  Cooler air from the thunderstorm sinks to the surface then spreads out ahead of the thunderstorm, effectively creating a small-scale “cold front” with a wind shift and a noticeable drop in temperature and dew point (much like a “traditional” cold front).  Outflow winds can easily gust into the 30-40 mph range and occasionally rise well above the 40s for brief periods.

These gust fronts can also serve as a lifting mechanism for the warm and humid air that it advances through.  As a result, the outflow boundary/gust front can generate new thunderstorm development.  If you watch us regularly, you may have noticed how we point out occasions where different outflow boundaries collide: intersecting outflow boundaries can produce explosive development of thunderstorms.

Our forecast for Friday calls for a drier day ahead.  We’ll start of Friday with a warm and humid morning -- like the past few mornings, expect sunrise temps in the mid 70°s for metro Baton Rouge.  But Friday afternoon’s forecast only calls for a 20% -- to maybe 30% -- rain chance under otherwise partly cloudy skies.  But then, “drier” usually means hotter: look for Friday highs up around 93° for metro BR, with some WAFB neighborhoods reaching the mid 90°s.

We still expect that cool front we’ve advertised this week to make it into south Louisiana over the next day or so before fizzling out along the coast.  The “drier” air (less humid, lower dew point temps) should allow for lows on Saturday and Sunday to slip back to something closer to 70° or so, but we’ll still see afternoon highs in the low 90°s.  Saturday should be a mainly dry day weatherwise, with rain chances at less than 20%.  By Sunday, however, the air will already have started to moisten up thanks to the return flow off the Gulf: we’ll set Sunday afternoon and early evening rain chances at about 30% to maybe 40% closer to the coast.

By next week, we’re back to typical summer-season weather: low to mid 70°s at sunrise, daily highs in the low 90°s, and scattered mainly-afternoon rains.

And in the tropics ... although Chantal lost her surface circulation yesterday, ‘her’ remnants have shown some hints of mid-level spin today.  As a result, the National Hurricane Center is posting this area of disturbed weather with a 30% chance of returning to depression or tropical storm intensity over the next two days.  Were it to re-develop, the latest computer guidance indicates little chance for the system to head into the Gulf.  However, that assumes that any new center of circulation will emerge between Cuba and the Bahamas.  Should the center develop elsewhere, we’ll have to re-assess the Gulf threat.  But for now, let’s just relax -- this doesn’t look like it will be a storm for us to worry about regardless of what happens.

Wednesday, July 10, 2013

Chantal Downgraded to a Tropical Wave

By Jay Grymes & Steve Caparotta

It proved to be a mainly-dry day across WAFB-land, with Titan9 Doppler picking up only spotty showers across the viewing area through the day. But we started with a very muggy atmosphere: dew points during much of the morning were in the mid 70°s for the Capital City. Thankfully the air “dried” a tad by the afternoon, but those dew points still hung in the low 70°s -- about typical for July.

Look for partly cloudy skies throughout the night with partly to mostly cloudy skies by the early morning. We could see a few showers to start the day on Thursday, although they will likely be focused over the coastal parishes. And it will be another warm and muggy start on Thursday, with Red Stick temps in the mid 70°s near sunrise.

Thursday afternoon should be a bit wetter than what we’ve seen the past couple of days -- we’re going with a 40% to 50% rain chance for Thursday afternoon and early evening. After that, our forecast reads like a fairly typical summer-season forecast for the Baton Rouge area: morning lows in the low to mid 70°s, afternoon highs in the low 90°s, and isolated to scattered mainly-afternoon rains each day.

A weak cool front is still expected to try and make it to the coast by week’s end. For now we expect it to arrive in the viewing area on Friday. Our thinking is that it will slow its southward advance on Friday into Saturday, while fizzling out as it passes over the area. 

Admittedly, the expected cool front is making the Friday and Saturday forecasts a little tougher than normal. We don’t expect the front to enhance rain chances much on Friday, and while we think we could get a brief shot of slightly less-humid air on Saturday, we don’t think that the impact will be enough to suppress rains on Saturday afternoon. For now, we’ll post a 30% to maybe a 40% rain chance for Friday afternoon and evening, and call it a 20% to 30% chance for Saturday. By Sunday, we expect to see coverage on the order of 30% to 40% for our viewers.

As for Chantal, she’s about “done” as of this afternoon. Shearing winds were mainly responsible for her steady demise over the past 24 hours, and as of mid-afternoon the Hurricane Hunter aircraft was unable to find a closed center of circulation. We’ll still be able to track what remains of Chantal for the next several days at least, but re-development appears unlikely given the hostile environment expected ahead of Chantal’s remnants. 

Tuesday, July 9, 2013

Scattered PM Rains Continue

By Jay Grymes & Steve Caparotta

A bit drier today than the past few days, although daytime heating was sufficient to fire-off isolated afternoon showers and a couple of t-storms across the viewing area.  Look for the weather to settle down by or before sunset, with a dry night ahead for just about everyone.
We’ll start Wednesday under partly cloudy skies with Red Stick area temperatures in the low 70°s around sunrise.  The thermometer will rise quickly through the morning hours, reaching the upper 80°s by lunchtime and topping out in the low 90°s for the afternoon.  Like today, only a portion of the viewing area gets rain -- we’re setting afternoon and early evening rain chances on Wednesday at about 30% under a sun/cloud mix.
For the time being, the forecast  for Thursday through Saturday reads about the same: morning lows in the low to mid 70°s, afternoon highs in the low 90°s, and afternoon and evening rain chances running in the 30% to 40% range for all three days.

The weather just might get a little more interesting as we head into the weekend.
First off, the cool front that we thought might make it too the Gulf Coast looks like it will fizzle out as it pushes through the state, although it might deliver a brief dose of slightly drier air Saturday into early Sunday.  At the same time, however, we think that the upper-level low currently to the east of the Florida Peninsula will have made its way westward and be positioned somewhere over or near the north-central Gulf.
This upper-low is an intriguing ingredient to the weekend weather outlook: depending on its location and intensity, it could either increase or decrease our weekend rain chances!  (Yes, we know -- that’s just about as non-committal as we can get!)  We’ll have to wait at least a couple of days to see how that shakes out.
And then there is Tropical Storm Chantal.  One could say that Chantal has been beating the odds over the past couple of days: more often than not, a relatively weak tropical storm moving at a speed of 25-30 mph would be struggling to survive.  But not Chantal -- in fact, while her satellite presentation is far from impressive, ‘she’ has ever-so-slowly been strengthening while racing to the west-northwest.
The 4PM National Hurricane Center forecast for Chantal takes her across Hispaniola on Wednesday and then up through the Bahamas on Thursday and Friday.  Actually, the latest round of forecast model runs hints at a slight shift to the west of that official track, closer to Cuba and then paralleling Florida’s Atlantic Coast by Saturday.  Another change evident in the NHC forecast is that the latest run fails to show the dramatic slow-down in forward speed into the weekend that was indicated in earlier forecasts.

For now, the current NHC thinking is that Chantal will most likely threaten the U.S. Atlantic Coast from northern Florida into the Carolinas.  However, enough uncertainty remains in play down the road that we need to keep an eye on Chantal.  Although we are putting the chances at the very low end (for now), we still can’t entirely rule out a turn towards the Florida Peninsula and an unwelcomed visit into the eastern Gulf.

Monday, July 8, 2013

Hot, Scattered T-Storms Next Few Days

By Jay Grymes & Steve Caparotta

The weekend forecast proved tougher than we had expected.  Some of you made it through both days with limited amounts of rain and no real problems, yet rain reports and radar returns showed some bull’s eyes of 3” to 4” of rain and more for a handful of locations across southern Louisiana and southwestern Mississippi.  Forecasting the “where” for those kinds of downpour pockets is impossible.

A scattered-to-numerous afternoon rain pattern returned during on Monday afternoon, fueled by a moist-and-unstable atmosphere, daytime heating and signs of a weak low spinning to the southeast over the coastal waters.  We expect the rains to back down into the evening and overnight, although spotty showers are possible overnight, especially closer to the coast.

Plan on something similar for Tuesday -- we’re going with a 40% rain chance for Tuesday afternoon and early evening.  Rain chances are expected to drop off a tad for Wednesday, but remain in the scattered category for Thursday and Friday.  Same is true for the weekend.

We’ve got to admit: the weather picture for the end of the week and the weekend is far from clear.  An upper-level trough over the U.S. and an upper-level low currently over the Bahamas will make the Thursday-through-Sunday forecast a tough one.

That upper-level low and associated tropical wave moving through the Bahamas is expected to continue moving westward and should be over the eastern Gulf later this week.  There is no impending threat for this complex to develop into a surface-based tropical system, but it does deserve monitoring.  If it makes it over the north-central Gulf, it could mean better rain chances for the weekend.  On the other hand, if it slows or stalls over the eastern Gulf -- that could mean a drier pattern for us on Thursday and/or Friday.

Then there is Tropical Storm Chantal, which earned ‘her’ name late Sunday evening.  Located over the tropical Atlantic, T.S. Chantal is just under 400 miles east of the Lesser Antilles, moving WNW at a brisk 26 mph (as of the 4PM NHC Advisory) with maximum sustained winds estimated at 45 mph.  Chantal has shown some strengthening today and the NHC anticipates some additional development over the next day or two.  On ‘her’ current track, Chantal should enter the eastern Caribbean on Tuesday and head towards the Greater Antilles during the mid-week.

For now, virtually all computer forecast models call for Chantal to slow her forward speed as ‘she’ cuts across the Greater Antilles (Puerto Rico, Hispaniola & Cuba) and then takes a more northerly track through the Bahamas into the weekend.  This scenario makes two assumptions:  (1) that interaction with the Greater Antilles weakens, but doesn’t destroy, Chantal’s surface circulation and (2) that an anticipated upper-level trough materializes over the eastern U.S. by mid- to late-week, helping to turn the system.

Given that we are talking five days out, there remains considerable uncertainly here, and we’ll be keeping an eye on this system right through the weekend.

Could things be heating-up in the tropics?  The low-latitude Atlantic “wave train” seems to be gaining some momentum.  In addition to Chantal, there is one, and possibly two, healthy waves marching behind ‘her’ from east-to-west.  Neither offers any immediate threat for development, but both will bear watching in the coming days.