Friday, June 29, 2012

The Heat Just Keeps Coming...

By Jay Grymes & Steve Caparotta

As we often say at this time of year, we can’t totally rule out a passing shower or two in our “next day” forecast, but for the vast majority it will simply be more of the same on Saturday: too hot, humid, and awfully dry with afternoon highs returning to the mid 90°s.
For Sunday, it’s once again back to the mid 90°s, and while we offer the slightest of rain chances at 10%, don’t count on any relief over the weekend.  We’re seeing more and more folks using the lawn sprinklers -- and for good reason. The same high pressure ridge in the middle and upper levels of the atmosphere that has accounted for record and near-record heat during the past week or more will remain mainly in charge through the weekend.
There are some signs that the ridge may weaken, albeit only slightly, and possibly shift to the west next week.  That should give us slightly better rain chances during the afternoons.  So our work week outlook, including the forecast for July 4th festivities, reads like a broken record: lows in the mid 70°s, highs generally in the mid 90°s, with a 20% to 30% chance of afternoon and early evening t-showers.  That forecast is still a tad shy of “normal” rain chances at this time of year (30% to nearly 40% for late June and July), and those highs still suggest warmer-than-normal weather will dominate the coming week.
And to add to the discomfort, the 3-month long-range outlook (July-August-September) from the NWS Climate Prediction Center calls for at least a 75% to 80% chance for temps to average “normal or above” for the remainder of the summer!  Is that air-conditioner in good working order?

Elsewhere ... although there is an easterly wave in the tropical Atlantic that the National Hurricane Center is watching, but any development will be slow to occur.  More importantly, there is nothing anywhere nearby for Gulf interests to worry about through the weekend or even early next week.

So please be careful in the weekend heat, don’t forget the pets . . . and as always, a big “Thank You!” to all of our Weather Watchers!

Wednesday, June 27, 2012

More Heat, Another 'Ozone Action Day'

By Jay Grymes & Steve Caparotta

Wednesday continued our run of unusually high temperatures, although not quite what we saw with the 101° all-time record highs set on Monday and Tuesday. While Baton Rouge’s Metro Airport (BTR) fell a tad shy of 100° today, the trade-off was the higher humidity levels through the day, making it feel just as “hot” as the prior days.

We saw a return of southerly winds today, and that means more low-level Gulf moisture. The added humidity meant that BTR’s Heat Index reached 100° by 11AM and stayed through throughout the afternoon (and will do so into the early evening, at least). In addition, the added humidity was just enough to power a couple of thunderstorms over SE Louisiana. But for many of us, those showers would have been welcomed relief from the brutal afternoon heat.

Now that the low-level southerly winds have returned, we can expect them to remain in place throughout the rest of the week and weekend. As we saw on Wednesday, the more humid air will probably help keep daytime highs in the mid to upper 90°s rather than the triple-digits, but the heat will “feel” just about the same. And as occurred on Wednesday afternoon, we can’t rule out spotty t-showers - - some producing brief but very heavy localized downpours. You’ll note, however, that our forecast remains “mainly dry” through the weekend, with only slight rain chances returning during the early and middle part of next week.

T.D. Debby picked up a little forward speed earlier today and exited the Florida Peninsula before sunrise this morning, moving into the western Atlantic. While we thought Debby might re-intensify once she entered the Atlantic and moved over the Gulf Stream, strong westerly shear throughout the day has meant ‘her’ demise, and as of 4PM the National Hurricane Center has declared that Debby has lost her tropical characteristics, closing the books on the fourth storm of the season.

Finally, today marks the 55th anniversary of Hurricane Audrey's landfall in southwest Louisiana. Audrey is the 7th deadliest hurricane in U.S. history and 3rd deadliest for Louisiana, trailing Katrina and the 'Cheniere Caminada' hurricane of 1893. Audrey also still stands as the strongest June hurricane on record to strike the U.S.

And despite making landfall well west of Baton Rouge, Audrey produced a peak wind gust of 69 mph in the Capital City. That nearly matches the 70 mph peak gust of Andrew in 1992...a storm that tracked MUCH closer to Baton Rouge.

Tuesday, June 26, 2012

More Record Highs Falling...

By Jay Grymes & Steve Caparotta

Another hot one today … it was 97° by 1PM at Metro Airport, with the day’s high topping out at 101°F, setting a new record for the date and topping a record that has stood since 1930 (more than 80 years).

As hot as it was, at least the dewpoints were in the 60°s through the day for most of us.  Not that dewpoints in the 60°s means “comfortably dry” air, but at least it wasn’t so overwhelmingly oppressive.  But from what we are seeing, that is going to change as well in the coming days.
The northerly flow that has delivered “drier” continental air to most WAFB neighborhoods over the past two days is expected to come to an end on Wednesday, with a more traditional southeasterly flow setting up by Wednesday afternoon and evening.  That will ultimately mean a return of Gulf moisture to our area, rising humidity and a muggier feel to the air as the week progresses.
There is a trade-off:  “drier” air heats up more easily and generally produces less cloud cover (which translates into more sunshine). The effect is that in many instances, summer days with a slight reduction in humidity will end up with higher afternoon temperatures.  By contrast, Gulf air with its higher water vapor content tends to generate more cloud cover, helping to block some of the solar loading.  In addition, “moist” air heats more slowly, so that afternoon temps during a more traditional summer day may not get quite so high.
So what will it be: very hot and slightly less humid or our traditional hot-and-humid weather?  From a “feels like” standpoint, very hot days with low humidity often end up with Heat Index numbers that are comparable to the days with higher humidity but not as hot (on the thermometer).
There are a couple of other issues to consider.  Those “drier” air days, with the northerly flow are often a little breezier than our traditional “return flow” days (days with windflow from the Gulf) – those breezes can make the heat slightly more bearable.  However, as generally sunnier days, those “drier” air days offer little or no respite from the intense sunshine, and the sun can add from 5° to 10° to the “feels like” temperature.  So for those stuck in the sunshine all day long, the lack of clouds can really take an additional toll!
Bottom line: most summer days in the WAFB viewing area are tough on anyone when too much time is spent without relief from the heat.  And this week is shaping up to be a bit more brutal than most summer days.  Take breaks, get into the air-conditioning occasionally if it is available, and try to limit direct exposure to the sunshine.  Don’t forget: loose-fitting, light-colored clothes, lots of fluids, even a hat or yes, an umbrella, helps!
T.S. Debby continues to weaken and made landfall this afternoon along the shores of the Florida ‘Big Bend’ region.  Debby picked up a little east-bound speed today, and now looks like she could be across the Florida Peninsula and into the Western Atlantic by late Wednesday or early Thursday.  The forecast still calls for Debby to return to tropical-storm strength after reaching the Atlantic, thanks to a little energy boost when she reaches the Gulf Stream.

Monday, June 25, 2012

More Record Heat Possible This Week

By Jay Grymes & Steve Caparotta

Looks like we’ve traded the threat of a tropical storm for excessive heat! Metro Airport’s 101° sets a new record high for this date, and today is the “hottest” day since August 18th of last year.

Our forecast through the coming week calls for mostly sunny days through Thursday, with highs each day climbing into the upper 90°s to around the century mark. For those working outdoors, add in the humidity and the effects of direct sunshine and the mid-afternoon Heat Index will have a “feels like” temperature closer to 110° to 115°! Needless to say, if you are going to be working outdoors, remember to take frequent “escape breaks” from the heat and drink plenty of water.

A building ridge of high pressure centered over the Southern Plains is reaching all the way to southeast Louisiana, and that ridge is the primary driver for the week’s extra-hot forecast. In fact, we are getting a little benefit from T.S. Debby’s circulation -- her counterclockwise flow is creating a north to northeast wind, transporting slightly “drier” (less humid) air into our WAFB neighborhoods. Dewpoints at Metro Airport this afternoon have dropped into the mid and even low 60°s -- think how much more oppressive the air would feel with our traditional summertime flow off the Gulf, with dewpoints in the 70°s!

As for Debby -- ‘she’ appears headed into Florida, and ‘she’ may be picking up a little forward speed along the way. But through much of today, Debby has weakened and become a little less organized, with peak sustained winds estimated at 45 mph. The current thinking is that Debby will remain at or near that intensity and that she’ll go inland somewhere in or near the “Big Bend” section of Florida as a minimal tropical storm on Wednesday. But Debby has already had a huge impact on Florida, with rains of more than 10” in some locations and a preliminary count of 18 tornadoes scattered across the peninsula.

Debby has also had a modest impact in Louisiana, prompting the NWS to issue a Coastal Flood Advisory for the southeastern coastal parishes and for the shorelines around lakes Pontchartrain and Maurepas. But assuming that Debby maintains an eastbound trajectory, the coastal advisory may be discontinued on Tuesday.

The NHC is not ready to close the book on Debby after ‘her’ Florida landfall: the NHC anticipates that Debby will weaken while crossing the Florida peninsula, but will emerge into the western Atlantic and potentially return to tropical storm strength! Stay tuned!

Friday, June 22, 2012

Hot & Dry at Home...Eyes on the Gulf

By Jay Grymes & Steve Caparotta

As we’ve been saying for a number of days: we can’t COMPLETELY rule out a passing shower or two in the coming days, but the vast majority of us will stay dry through the weekend and into the first couple days of next week. We won’t even “mention” rain chances for the weekend, and put only “spotty showers” in the forecast for Monday into Tuesday.

It’s the temperatures that will be our local weather story, with morning sunrises in the 70°s and afternoons in the mid to upper 90°s for some WAFB neighborhoods. It’s a yard-work weekend for many of you: PLEASE be careful in the heat!

We bring slight rain chances back into the forecast by mid-week, but to be honest, our confidence is not all that great about the local forecast by mid-week given the uncertainty with regard to the disturbed weather in the southern Gulf.

And that is where our “weather attention” will be focused over the next several days. The disturbance in the southern Gulf continues to show signs of potential development, but the NHC and other tropical experts are still having a hard time finding a center of circulation. Until they can define that core, forecasts for direction, speed and intensity will remain a bit up-for-grabs. 

What we currently are seeing in the models are two basic schools of thought: several of the global computer models show a northwest-to-west solution after a couple of days, while other models are still pointing to a northeast-to-east solution. In the interim, most of the models agree that whatever it is will likely drift slowly northward through the central Gulf for a couple of days. 

Obviously, the failure to clearly define a center, coupled with this large departure in the model trends after a few days, leaves us with very low confidence as to what is going to happen between now and early next week. Satellite imagery shows a rather broad low- to mid-level counter-clockwise circulation over the southeastern Gulf, and imbedded within that there are a handful of places with what appear to be hints of a surface spin, but nothing that jumps out and says, “Here is the center!”

The general atmospheric environmental conditions over the eastern and southern Gulf appear to be at least moderately favorable for development and water temps in that part of the Gulf are in the low to mid 80°s -- more than sufficient to fuel a tropical system. It seems likely that we will have a tropical depression by sometime on Sunday (T.D. #4), and while our thinking is that this will be a rather slow-developing system, we won’t rule out the possibility of this becoming Tropical Storm Debby by the end of the weekend.

And if you are curious: Chris is no more, having lost his tropical characteristics; remnants likely will merge with an extra-tropical low within the next 24 hours.

So stay linked to WAFB … through the TV, your phone app and at, and we’ll keep you informed as to conditions over the Gulf.

Thursday, June 21, 2012

More Attention on the Southern Gulf!

By Jay Grymes & Steve Caparotta

Afternoon highs will continue to creep higher over the next few days, and while we can’t say “absolutely 100% rain-free” through the weekend, any showers that do develop will be spotty and short-lived.

We still expect some mid and even some upper 90°s in the viewing area by the weekend and into early next week -- so PLEASE be careful in the heat, especially if you are going to be in the direct sun which can add another 10° or more to the heat load!

For most Louisiana and Gulf Coast interests, the BIG developing weather story concerns the thunderstorm activity and low-pressure trough extending over the southern and southeastern Gulf. This afternoon, the National Hurricane Center (NHC) confirmed an "invest" ('area of tropical interest') in the extreme southern Gulf along the northern coast of the Yucatan Peninsula. (You might remember that the WAFB storm Team pointed to the ‘spin’ over the northwest Yucatan on Wednesday evening.) Satellite movies show broad-scale spin along the northern Yucatan Coast, and the NHC has posted a 50-50 chance for tropical cyclone development in the next two days.

Now that there is a focus point for a center of circulation, we'll see what the computer guidance has to say about direction and rate of development during their evening runs. Given the extreme southern location, the earlier consensus by some of the reputable models for this being a Florida threat may no longer apply! In fact, our 3PM suspicion is that the models may now point the storm more towards Texas or Mexico, or worse yet, let it spin and meander in the southern and central Gulf.

Rapid development does not seem very likely at this point, but ANYTHING in the Gulf at this time of year deserves our attention. And as we head into the weekend, many people pay less attention to the weather -- don’t be one of those! Keep your eyes, ears, TVs, computers and mobile devices linked to WAFB, and we’ll keep you informed.

And while we’re talking tropics, Chris has done the almost unthinkable and continued to intensify, reaching Category 1 hurricane intensity earlier today! As of 4PM, Chris had weakened and returned to tropical storm strength, and slow-but-steady weakening is expected to continue over the next two days. While Chris is no threat to land, his history reminds us that when it comes to tropical systems, we still have a LOT to learn!

Friday, June 15, 2012

A Bit Drier Saturday

By Jay Grymes & Steve Caparotta

Scattered afternoon showers and t-storms have broken out over the WAFB region, with the most widespread action occurring over the southernmost parishes.  We’ll see these storms ease back by or before sunset with skies becoming mainly fair before midnight.
We’ve backed off on our earlier rain chances for Saturday, now going with only isolated afternoon rains, and set Father’s Day (Sunday) rain chances at a modest 30% -- both days should be good for most backyard BBQs.  And the sunrise temps for both Saturday and Sunday should be reasonably comfortable by June standards, running in the upper 60°s for many WAFB communities.  Highs both days will top out in the upper 80°s to around 90°, with some neighborhoods getting a cooling shower around the heat of the day.
You may recall that we were closely tracking two disturbances over the Southern U.S. the past couple of days -- one that was over our viewing area last night and the other over the Mobile-Pensacola strip of the Gulf Coast.
The disturbance that was essentially almost overhead yesterday as well as the weak trough/stationary front that had lingered over the Lower Mississippi Valley for a number of days have lost just about all of their definition and are no longer serious contributors to our weather. 
As for the disturbance to our east along the Gulf Coast, it looks like it has headed south into the NE Gulf and won’t be much of a weather factor for us over the weekend.  However, some of the guidance suggests that it will once again take on a westbound run in the next day or two and could work its way across the northern Gulf, possibly even earning some real attention early next week.

With the exception of that northeastern Gulf “spinner” that we’ll be watching (closely), our 7-day forecast is rather benign.  Unless that Gulf low becomes something more ominous, we’ll plan on 20% to 30% rain chances for just about every day next week, with lows in the low 70°s and highs around 90°.

Thursday, June 14, 2012

Scattered Storms into the Weekend

By Jay Grymes & Steve Caparotta

Scattered showers and t-storms continue around portions of southeast Louisiana this afternoon, but fortunately most of the storms have remained below severe limits today.

Doppler radar estimates are showing some 2” to 3” rain totals for today over portions of Assumption, St. James, St. Charles, Terrebonne and Lafourche parishes, with 2” to 3” totals also indicated over sections of Wilkinson County and East Feliciana Parish (mainly from the morning storms). 

Today’s rains will subside into the evening hours and most of us will stay dry through the overnight. However, the atmosphere remains very unstable, so we can’t rule out an isolated shower or storm overnight, especially for the southernmost parishes.

Today’s clouds kept Thursday highs in the 80°s for most of us, and those clouds will likely linger through most or all of the night, keeping temps in the 70°s for most of us.

Today’s rains -- a bit more widespread than Jay had expected -- were the product of the stubborn surface trough/quasi-stationary front that continues to meander over the lower Mississippi Valley plus the influence of the mid-level disturbance that was over the Red River valley yesterday.

That Southern Plains disturbance -- the same system that produced large hail in the Dallas metroplex -- took on a more southeasterly trajectory last night. While it became rather diffuse as it approached the Gulf Coast, it added enough lift and energy to kick-off those somewhat surprising Thursday morning rains and storms. There were even reports of hail in a few locations!

If you remember, on Tuesday we pointed out two disturbances: the Red River/Southern Plains system and the “spinner” over the Gulf Coast region extending from around Mobile Bay eastward into the Florida Panhandle. That Mobile/Pensacola system is also becoming less defined, but its remaining energy appears to be headed west, providing potential lift and support for Friday’s rains. It could even be a factor into Saturday, especially for areas west of the Atchafalaya Basin as it continues moving west.

The weekend outlook is not bad, just not great either. For now, we’ll go with a 30% chance of mainly afternoon showers and storms on Saturday with a 20% rain chance for Sunday afternoon. Highs for both days look to run in the upper 80°s to around 90°.

Wednesday, June 13, 2012

Back to the 90°s...Modest Rain Chances

By Jay Grymes & Steve Caparotta

Most WAFB neighborhoods stayed even “drier” than we had expected on Wednesday, with only spotty afternoon showers developing over southern Louisiana, and most of those were to the west of the Atchafalaya Basin. And many didn’t quite make it to 90° -- I doubt that there is any complaining about that!

We still have that rather diffuse surface boundary meandering around the lower Mississippi Valley and Gulf Coast -- something between a surface trough and a quasi-stationary front. It is expected to continue hanging around the Bayou State and coastal waters through the rest of the work week, providing a modest lifting mechanism for the region. On the other hand, mid/upper-level ridging is limiting cloud coverage today, and more importantly, vertical cloud development. Without the vertical growth, our summertime cumulus clouds just can’t become rainmakers. And that weak ridging is likely to remain in place through the weekend and into next week.

Still, with the surface trough, occasional weak mid-level disturbances sliding by and a relatively warm, moist and unstable air mass at the surface, we have most of the ingredients to fuel some afternoon showers and a few rumbles of thunder over the coming days. We’ll go with 20% to 30% rain chances over the better part of the next seven days, with the regional upper-air ridging being the one obstacle to more widespread afternoon rains.

Expect lows to run between 70° - 73° just about every morning for metro Baton Rouge, with afternoon highs near or just above 90°: warm, almost hot -- but just about normal for mid June. Keep in mind that Heat Index numbers will likely be in the 90°s for a number of hours each day, with peak Heat Index numbers approaching or even topping 100° and occurring in the late afternoon hours.

And in the tropics, for the time being all looks fairly quiet -- great news after that unusual start in the month of May!

Thursday, June 7, 2012

A "Wet" Run of Days Ahead!

To quote Annie Lennox, “Here comes the rain again!” 

In a pattern not too different from Wednesday’s outbreak, a relatively “quiet” sky through 1PM on Thursday changed quickly, with afternoon thunderstorms popping up across a good bit of the viewing area. But the good news was that Thursday’s round of storms wasn’t nearly as “energized” (with lightning and hail) as some of the t-storms that we dealt with on Wednesday!

And we expect showers and storms to return each day: Friday, Saturday and Sunday!

Why does it seem like these storm “pop up” all at once rather than slowly develop and spread across the region? Our summer heat plays a major role in our afternoon t-storms, which is why we can go from a “quiet” sky like we had today at about 1PM today to storms popping everywhere just two hours later! The entire process can get rather involved and detailed, let’s me try and offer a basic explanation that covers the highlights.

When we look at the temperature and humidity of the air in the morning, we can calculate a “convective temperature.” This is the temperature that is warm enough to make air with a particular temperature/humidity combination rise rapidly and lead to clouds and ultimately storm development. Once the air near the ground reaches that “convective temp,” storm development is likely and can be very quick under the right conditions.

In general, the more humid a summer air mass is, the lower its convective temperature. So our traditional muggy south Louisiana air is often more than primed for afternoon storms, especially if it’s a sunny afternoon. Remember, that is exactly the way things started on our stormy Wednesday, and the same was true this afternoon. And yes, we expect a similar situation for Friday as well.

The quasi-stationary front meandering over south Louisiana and over the northern Gulf waters is helping as well, adding a little extra nudge (lift) to the warm and humid air. Remember, the warmer and more humid the air, the more “unstable” it is. We all know the phrase, “hot air rises.” But hot-and-humid air rises even more rapidly -- the more unstable, the faster it will tend to rise.

And for you weather nerds, our monster downpours just south of downtown area on Wednesday may not rank as an all-time record rain, but it certainly grabbed my attention. Radar estimates of more than 7” in the core of the storm were confirmed this morning -- the raingage at the LSU Geosciences Complex captured a whopping 7.35” of rain, most of that falling in four to five hours. A look at “rainfall/recurrence” information shows that for southern EBR Parish, a rain of 7”+ in about six hours ranks as a “once-in-50-years” event (on average)!

Now remember, a “once-in-50-years-rainstorm” is one of those statistical critters -- the label can be highly misleading if not interpreted correctly. The statistical ‘truth’ is that there is a 2% chance of such an event coming in any year. As such, although it would be extremely unlikely, it is remotely possible that we could see a “repeat performance” at almost any time.
Think of it like “snake eyes” (double ones) with dice: the chance of rolling snake eyes is very low, only 1-in-36 (less than 3%). Yet anyone who’s played backgammon or spent time at the casino tables knows that “snake eyes” do come up twice in a row! Hardly ever, that’s true -- but it DOES happen!