Friday, July 25, 2014

Hot, Mainly Dry Weekend

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- hot & mainly-dry through the weekend
- an approaching ‘cool’ front next week?

Our thinking hasn’t changed much over the past few days. Our “isolated” coverage today was along the lines of what we expected and we think it will be even drier through the weekend. We’re going with rain chances at 20% or less for Saturday and spotty showers at best for Sunday. 

So it’s shaping up to be a “sunscreen” weekend for those that take advantage of a pair of mainly-dry days. But be careful in the heat, whether it’s yard work duty, around-the-house projects, a day on the links, or some “me time” in the boat. We’re looking at highs in the low to mid 90°s for both days -- a forecast that calls for two afternoons that may rank among some of the ‘hottest’ days of the summer so far. 

You know the routine: lots of water and breaks in the shade. These are the kind of days that can keep our area EMS professionals busy with heat-related calls.

The heat-maker? That upper-level ridge that we’ve been talking about for the past week. Although it remains centered to our west, the ridge (high-pressure aloft) will continue to expand eastward into the weekend. That will put us under the eastern flank of the “heat dome” -- maybe not enough to totally shut-off rain chances but certainly enough to chop the rain chances down to 20% or less for Saturday and Sunday. 

As we head into next week, the ridge will again retreat to the west as an upper-trough (southward dip in the jet stream) digs into the eastern half of the country. And for now at least, our guidance into next week is showing signs of that trough helping to drive a cool front into the viewing area around Tuesday. The NWS Weather Prediction Center currently shows the front digging southward to the coast and then lingering there into Friday. That scenario means two things: increasing rain chances with the front’s approach and passage and then a break in the humidity for a couple of days with highs possibly topping out in the 80°s.

Now, we must admit that these 5- to 7-day summer frontal forecasts often don’t pan out, with the proposed front stalling before arriving in south Louisiana. But the guidance has been hinting at this possibility for a couple of days now, so we’ll remain cautiously optimistic about a modest break from our usual summer heat-&-humidity sometime next week.

In the meantime, all is quiet in the tropics ... quoting the National Hurricane Center: “No New Tropical Cyclones Are Expected to Form During the Next 5 Days.”

Thursday, July 24, 2014

A Little Drier .. and a Little Hotter ..

WAFB First Alert Quickcast:
- getting even “drier” in the coming days
- could see some mid 90°s over the weekend
- all “quiet” in the tropics

Yesterday we mentioned the slow breakdown of the upper-low that has been skirting from east-to-west along the Gulf Coast .. and as of this afternoon that feature is just about gone. What we did see in the way of rainmakers today was a bit of a combination of the last “hello” form the upper-low -- mainly over Acadiana -- and something a little more like a summer sea-breeze for the southeastern parishes.

As is usually the case at this time of year, the area rains will dissipate as we lose the energy of daytime heating. So it’s fair skies tonight and into Friday morning, with sunrise temperatures in the low 70°s for metro Baton Rouge. As we head into Friday afternoon -- and throughout the weekend -- the upper-level ridge to our west will expand and shift a bit eastward. That means its influence on our regional weather will increase in the coming days.

You know that ridges aloft (upper-level high pressure) tend to inhibit vertical cloud growth. In simple words, not only does upper-air ridging reduce rain chances, but it usually means more sunshine. And in the summer, more sun often means higher temperatures.

We won’t go completely “dry” over the next few days. In fact, I must acknowledge that our in-house RPM model wants to make things rather wet for Friday, apparently picking up on a weakness along the Gulf Coast under the eastern fringe of the upper-air ridge. But I’m not buying that, at least not the RPM’s 40% to 50% coverage for Friday afternoon -- nor are some of our other reliable short-term models. So I’m going with rain chances at about 20% or so for Friday, then on the order of 20% for Saturday too. I expect the ridge to be most dominant by late Saturday into Sunday, so for Sunday, I’m thinking rain chances at 20% or less.

Bottom line: the weekend is looking pretty good for some outdoor fun or work, but be ready for temperatures in the low to mid 90°s. Heading into next week, the upper ridge begins to shrink and retreat back to the west again, along for increasing rain chances. In fact, some of the extended guidance is trying to drive a summer ‘cool’ front down to the Gulf Coast around mid-week. Nothing to get excited about just yet -- that’s a little too far down the road for confidence -- but it will certainly be something to watch.

And in the tropics, there are a couple of weak waves floating in the Atlantic -- one being the remnants of TD #2 -- but that’s about it. Neither wave shows any potential for development in the near-term. So, no threats for now and none anticipate by the NHC in the next five days or more.

Wednesday, July 23, 2014

- afternoon showers and storms will subside into the evening
- rain chances decreasing in the coming days
- “Goodbye” to T.D. #2
The upper low that we’ve been tracking the past few days made its way over southeast Louisiana today, bringing better rain chances with it. While most of the action was along the coast and over the coastal waters this morning, daytime heating added just enough “umph!” during the afternoon to join up with the low and kick-off scattered afternoon showers and storms over the region. We expect the rains to subside into the evening as we lose the solar energy, with a quiet night for most WAFB neighborhoods.
After a mainly-dry start to the day with morning lows in the low 70°s, afternoon showers and a few t-storms return to the viewing area for Thursday. But unlike earlier today, we’ll set rain chances for Thursday at only 30% or so -- less coverage in general. The rationale is that the upper-level low currently nearly overhead will shift a bit to the southwest -- and more importantly – will become “stretched” and less defined. In effect, it will lose its impact on the local weather, allowing the broad upper-level ridge over New Mexico and west Texas to re-expand eastward and become a more dominant factor in our regional weather.
Since we’ll still be on the eastern fringe of the upper-high rather that underneath it, the ridge won’t shutoff rain chances, but it will inhibit development on Thursday and become even more dominant for Friday and the weekend.
As a result, we’ll go with rain chances at 20% or less for Friday, Saturday and Sunday - - and possibly include Monday too. But you know the drill: high-pressure aloft (upper-level ridges) mean less clouds and reduced rain chances, but the increased sunshine usually means a bit of a warm-up. We’re expecting low to mid 70°s for morning starts by Friday and into the weekend, with afternoon highs in the low 90°s for most WAFB communities, while a few could sneak into the mid 90°s on Saturday and Sunday.
“Goodbye, T.D. #2 … and good riddance too!” T.D. #2 succumbed to wind shear and ‘dry’ air and was downgraded to a remnant low at 10am this morning. While #2’s “bubble” of clouds is still evident on satellite imagery, the associated convection (thunderstorm activity) has faded and there is no evidence of a low-level circulation. The end of T.D. #2 came a little more quickly than had been expected by the National Hurricane Center experts, but as you recall there was never any perceive threat for the Gulf of Mexico. But let’s remember, we are still early in the Hurricane Season, and nearly 70% of Louisiana’s past tropical ‘visitors’ came during August and September.

Monday, July 21, 2014

WAFB First Alert QuickCast:
- mainly dry for Tuesday
- better rain chances for Wednesday & Thursday
- watching T.D. #2 in the tropical Atlantic

The weekend didn’t turn out quite as wet as we expected, but it was far from a ‘pretty’ Saturday and Sunday either. However, for most WAFB neighborhoods, we had a little opportunity for Friday’s big rains to run-off and sink-in.

The good news is that today was -- and tomorrow should be --mainly-dry days around the viewing area. Note that we said “mainly-dry,” which means we can’t rule out a shower or two, especially during the mid to late afternoons. One thing seems certain: the lawns and the mosquitoes are happy. (If you get a few minutes,“walk your yard” and dump any unintended containers holding water. This can be a great lesson for the kids too.)

But with less cloud cover and reduced rain chances comes a return of full-bore summer heat. After a morning start in the low 70°s for Tuesday, most WAFB neighborhoods will see highs in the low 90°s -- in fact, we won’t be surprise to see a couple of communities hit the mid 90°s. And as you know, with our Gulf air in place, that translates into Heat Index readings (‘feels like’ temperatures) that will peak around 100°or so. And remember, the Heat Index applies to the shade -- in direct sunshine, the Heat Index can go up another 10° to 15° under the right conditions. (So please be careful in the heat.)

An upper-level ridge to our west will help maintain a northwesterly flow at the upper levels and keep a bit of a lid on the atmosphere through Tuesday -- hence, our forecast for “mainly dry.” However, as we head into Wednesday, the guidance is hinting at a weak mid-level low moving into the central Gulf Coast region from the east. That low will provide enough lift to generate afternoon rains for Wednesday and Thursday before exiting the area. At this time, we’ll go with scattered showers and t-storms -- mostly the afternoon variety -- for both days. For Friday and the weekend, it looks like it might be a little drier, with rain chances currently posted at 20% to 30% for the three days.

And in the tropics? The National Hurricane Center (NHC) is has upgraded ‘Invest 92L’ in the central tropical Atlantic to Tropical Depression #2. The current official forecast keeps T.D. #2 on a west-to-WNW track over the coming days without further intensification. And more importantly, the NHC has T.D. #2 fizzling out near the Lesser Antilles on Thursday, ripped apart by strong wind shear centered over the Caribbean. The bottom line: T.D. #2 does not appear to be a threat for the Gulf.


Tuesday, July 15, 2014

Beautiful Day Ahead on Wednesday!

By Jay Grymes & Steve Caparotta

WAFB First Alert QuickCast:

- front moves through the region later this evening
- clearing and much less humid for Wednesday
- rains return for the latter half of the week
The ‘cool’ front we’ve been talking about for the last several days is still on track to arrive in the viewing area later this evening and makes its way south and into the coastal waters tonight and into Wednesday morning.  
And of course, the rains will make for a messy evening commute.  However, once the front moves through, we’ll get a nice break from the normal summer humidity.  Too bad the respite will be rather short.
We’ll keep isolated showers in the overnight forecast, mainly due to rains along the coast as the front sags south over the northern Gulf.  By Wednesday morning, skies should be clearing nicely for the Red Stick with morning lows in the upper 60°s for the northern half of the WAFB viewing area.  Mostly sunny skies will mean Wednesday afternoon highs up near 90° for many of us, but the ‘continental’ air mass in place will mean dew points in the low to mid 60°s for many of us tomorrow.  For south Louisiana, that is unusually ‘dry’ air and should make for a fairly comfortable day by July standards, even with those summer-like highs.
Much -- maybe even most -- of the WAFB viewing area will visit the 60°s once again for Thursday morning, but during the day the front will display a steady northward retreat.  By Thursday afternoon and evening, our typical humid Gulf air mass will be back in place.  In fact, we’ll even add in a slight rain chances -- at 20% to 30% -- for Thursday afternoon and evening as the unstable Gulf air displaces the drier air from the north.
Our forecast turns especially wet for Friday and the weekend: we’re going with rain likely for all three days.  What’s more, while we’re not calling for day-long rains over the three-day period, these won’t be ‘afternoon-only” rainy days either.  Although the majority of the rains will be during the latter half of the day, showers are likely to start popping up well before the lunch hour on all three days.
After a somewhat early start to the 2014 Hurricane Season -- thanks to Arthur on July 1st – all has remained “quiet” in the tropics since ... and there are no suspect areas for potential development through the next three to five days, at least.

Monday, July 14, 2014

More Wet Weather on Tuesday

By Jay Grymes & Steve Caparotta

WAFB First Alert QuickCast:

- better rain chances for Tuesday
- another July cool front at mid-week
Although today’s storms were somewhat limited in areal coverage, a few of them showed goodly amounts of lightning as they bubbled up.  They included a “healthy” thunderstorm that rolled right over downtown Baton Rouge between 3:15-3:45pm, delivering a little rain to our WAFB studio.
Yet the majority of WAFB communities stayed dry through Monday afternoon and evening.  However, the WAFB First Alert forecast for Tuesday shapes up to be considerably different. 
A July ‘cool’ front continues to sag southward towards the Gulf Coast.  It doesn’t arrive in the WAFB area until very late Tuesday or Wednesday morning, but it will be close enough on Tuesday afternoon to add lift to an already unstable air mass.  The result: our Tuesday afternoon and evening forecast reads “showers and t-storms likely.”  In fact, while we are not expecting a widespread severe weather outbreak, we’ll be on-guard for some strong to isolated severe storms. 

Tuesday’s action should take much of the stormy ‘punch’ out of the air mass as the front sags southward and stalls over the coastal waters by Wednesday afternoon.  That should mean a “drier” feel to the air on Wednesday as a continental air mass makes a brief visit to the viewing area.  Unfortunately, this frontal passage won’t be quite as dramatic as the one we enjoyed over the July 4th holiday weekend.  The air this go-around won’t get quite as cool and it doesn’t look like a complete dry-out either -- we’ll carry 20% to 30% rain chances for Wednesday and Thursday.  What’s more, the front will begin a retreat to the north as a warm front on Thursday.  
By Friday, we’ll be back in the “warm sector” (the south side of the front with moist and unstable Gulf air in place), and that will mean a return to increased rain chances.  In fact, we’re calling for 50% to 60% rain chances for Friday, Saturday and Sunday -- so it’s not looking like a very pretty weekend ahead right now.

But hey!  Two cool front in the month of July is far from the norm, so let’s enjoy the good fortune for now.  And here’s a bit of more good news: all quiet in the tropical Atlantic and no signs of development potential through the upcoming week.

Thursday, July 10, 2014

A Bit Drier into the Weekend

By Jay Grymes & Steve Caparotta

WAFB Storm Team QuickCast:

- pattern turns a little ‘drier’ for the next several days
- some may flirt with mid-90°s over the weekend

Take a closer look at the radar animations this afternoon and early evening and focus on the movement of the showers and storms. The movement today was different from the past two days. 

On Tuesday and Wednesday, we saw a number of storm clusters moving from the north or northwest towards the south and southeast. As we’ve mentioned in the past, the storms with more of a north-to-south motion often display greater lightning activity than storms moving from the Gulf inland. That south-to-north (or SW to NE) was the today’s pattern compared to the two previous days. 

Yet a look at the motion over the broader region this afternoon still shows active storm clusters by-passing Louisiana to the north and east and heading into the southeast states, continuing with a NW-to-SE motion, running in the flow of the upper-level trough positioned to our north and northeast. But for our area, today’s storms had more of a “sea breeze” appearance, a pattern more typical for the summer season along the central Gulf Coast.

We expect high pressure to become a more dominant player in our local weather over the next few days -- that means we’ll back down on the rain chances. Now do understand, we are not talking about out-and-out entirely dry weather, but we’ll run with rain chances in the 20% to 30% range for Friday, Saturday and Sunday -- down from the 30% to 40% numbers we’ve been posting for the weekend over the previous few days.

Of course, at this time of year lower rain chances usually mean less cloud cover -- and that means more sunshine and higher afternoon temperatures. In fact, much of the guidance is calling for highs in the mid 90°s for most of our viewing area for the upcoming weekend. That said, while we won’t be surprised to see some communities reach 95° or more over the weekend, we’ll call for highs a couple of degrees lower than that for most WAFB neighborhoods. But let’s face it: what is the ‘real’ difference between 93° and 95°?

Into the extended outlook, we’re getting some hints at another mid-summer cool front trying to make its way south and into the northern Gulf. Frankly, we are always a little skeptical of these longer-range projections: too often, the fronts fail to develop the southward momentum suggested by extended-outlook forecast models. But it does look as if a front could at least get close enough to add to the local instability and lift. As a result, we’ll look for improved rain chances by the middle of next week. Let’s see if it really pans out.

And in the tropics, the National Hurricane Center and the U.K. Meteorological Office agree that there are no potential developments in the works for at least the next four or five days.