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.

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.

More Rain This Weekend

The transition toward a wetter weather pattern began across south Louisiana and SW Mississippi today. While rains have been pretty manageable around metro Baton Rouge through late afternoon, radar estimates show widespread totals of 1 to 4 inches in our coastal parishes and a band from northern W. Feliciana Parish extending into parts of Wilkinson and Amite Counties in SW Mississippi where 2 to 5 inches or more of rain has fallen today!

Given the impressive totals we’ve seen in some locations today and the expectation of more rainfall to come this weekend, it’s easy to see why a Flash Flood Watch has been posted for parts of the WAFB viewing area. The Flash Flood Watch currently includes areas along and east of I-55, along with Terrebonne, Lafourche, St. John the Baptist and the parishes surrounding metro New Orleans. While I do agree that these are the areas most likely to see some heavy rainfall, the band from W. Feliciana in to SW Mississippi this afternoon serves as evidence that heavy rains could fall outside of the watch as well.

We’ve been talking about it for days…the increasing rains this weekend will be compliments of a deep surge of tropical moisture moving in from the Gulf. It’s a rather complex setup, but suffice it to say all of that moisture plowing inland will result in widespread showers and t-storms.

Loosely tied to all of this mess is a weak area of low pressure in the SW Gulf of Mexico. The National Hurricane Center gave development chances a slight bump this afternoon, now listing them at 20% over the next 48 hours. As you can see, the odds of development appear to be fairly low and the primary threat from this system will be heavy rainfall along sections of the Gulf Coast. In perhaps a small bit of good news for us today, most of our guidance has trended a bit farther south and west with the track of the low into Texas, which means it should have less of an influence on our already wet weekend forecast.

So how much rainfall can we expect? Honestly, I think most of our guidance has been running too low. Including today, rain totals by the end of the weekend will likely range from 2 to 4 inches around metro Baton Rouge. Closer to the coast, I think 4 to 6 inches is a good bet, with the potential for some much higher totals. And as we saw today, there can also be some localized bull’s-eyes with higher amounts farther inland as well.

And while I don’t think rains will be quite as widespread next week, our extended outlook does feature rain chances near or slightly above-normal through the balance of next week. Keep those umbrellas handy!

Wet Weekend Ahead!

It wasn’t an entirely rain-free day across WAFB-land, but it was certainly “quieter” weather-wise compared to what we saw on Wednesday, especially across the Baton Rouge metro area. Isolated showers this afternoon should wind down nicely as we head towards sunset, leaving us with a mainly-dry window at dark for enjoying the local fireworks, no matter where you are.

 

 

At the surface, a weak, quasi-stationary front continues to meander over southeast Louisiana, but that front is losing some of its definition and is slowly fizzling out. At the same time, the unusual upper-air trough over the center of the U.S. remains in place. On Wednesday, these two features teamed up to focus showers and storms over metro BR. By contrast today, the trough is pulling less “dry” northern air into the Gulf Coast region -- instead, in its current position it is tending to enhance a warmer and more humid southwesterly flow aloft. At the same time, the weakening front is less of a factor for generating afternoon rains, even though the air across most of the WAFB viewing area is moistening up.

 

After a run of days with dew point temperatures frequently in the low to mid 60°s, it’s looking like upper 60°s to low 70°s are returning -- something closer to July norms. Yes, our traditional Gulf humidity is on the way back.

 

 

Your attention likely will turn to the Gulf over the coming days after a look at the satellite loops. A broad area of low pressure extends across the entire Gulf, from the Florida Panhandle all the way to the Yucatan Peninsula. We’ve talked about this situation already this week: one could argue that it was two distinct areas of low pressure that have essentially merged into one large rain-making mess. That mess will continue a slow march towards the west and northwest along the central Gulf Coast over the coming days, and that means very good rain chances for Friday and the weekend.

 

The National Hurricane Center continues to post the southern portion of this area -- along and over the Yucatan Peninsula -- with a 10% chance for tropical development over the next 48 hours. We’re good with that probability -- there is too much shear over the northern and western Gulf for development there ... and simply too little organization or definition over the southern Gulf for anything to develop anytime soon down there. 

 

 

But get ready for some rainy weather, especially our coastal communities. The Florida Panhandle has been hammered these past few days, with estimates of 4” to as much as 10” of rain - - localized totals there potentially top a foot of rain! While we are not expecting anything quite like that over south Louisiana, we should prepare for a run of wet days. Plan on scattered-to-numerous showers and t-storms on Friday with rain likely (60% to 70% chances or better) for Saturday and Sunday.

 

I’m thinking rains of 1” to 2” -- with locally higher totals -- along and north of the I-10/12 corridor by the end of the weekend. Totals will be greater as you get closer to the Gulf: coastal communities should plan on 2” to 4” or more, with some localized big bull’s eyes as the Gulf low pressure region moves from east to west.

 

 

And elevated rain chances will probably continue into the first half of the upcoming work week. Oh well, I suppose that the backyards and gardens will love it?

Isolated T-Storms for the 4th

By Jay Grymes & Steve Caparotta

Based on the afternoon radar trends, today’s rain coverage was a little bit more widespread than we expected.  But you may have noticed that the rains were focused along a narrow SW-to-NE band.  What was a bit of a bigger surprise was the “Slight Risk” for severe weather posted by the NWS Storm Prediction Center (SPC) for Louisiana southeastern parishes for today and tonight.

If you were watching the regional radar trends through the day, you were seeing the showers and t-storms riding from SW to NE along the stalled frontal boundary draped over SE Louisiana, being supported by mid-/upper-level southwesterly flow.  We expect that front to continue to linger over the region into Thursday before fizzling out.  That SW-to-NE transport is being generated at the base of the upper-level trough (a southward dip in the jet stream) that we’ve talked about the past few days.  Keep in mind that the location and southward extent of this trough -- and its upper-level “closed low” over the Missouri Valley -- are rather unusual for this time of year.

With Louisiana near the “bottom” (southern end) of the trough, we’re in position for mid-/upper-level southwesterly flow associated with the jet stream flow around the trough.  That upper-level transport coupled with low-level moisture coming off the Gulf is fueling today’s rains.  In addition, that combination is aided further by the lift created along the weak stationary boundary, provides a set-up for a few stronger t-storms -- that’s why the SPC has flagged SE Louisiana for the “Slight Risk.” 

Although the SPC’s risk advisory is in effect until early Thursday, we suspect that the severe storm threat will decline after this evening’s sunset. However, the southern parishes should be ready for off-and-on passing showers throughout the night.  So we’ll go with spotty-to-isolated showers through the overnight, with the better chances for showers and storms closer to the coast. 

Our forecast for Independence Day celebrations remains essentially the same as we’ve said through the week.  After a mainly-dry start to the day, we’ll go with a 20% to 30% chance of mostly afternoon and early evening showers with an afternoon high around 90° or so.  You may notice that the humidity on Thursday will still be a little on the low side for July -- we think we’ll enjoy at least one more day with dew point temperatures lingering in the 60°s. 

We can’t rule out a spotty shower or two during the later evening hours on Thursday -- around “fireworks” time -- but most of the rain should be out of the region soon after sunset.

Also, as we’ve been mentioning the past few days, the outlook gets notably wetter for Friday and into the weekend.  A broad area of low pressure (an easterly wave headed to the west)  currently extends over the eastern and southeastern Gulf: that feature will come into play for the central Gulf Coast’s weather by Friday and Saturday.

In fact, we have a pair of weak low pressure areas in the Gulf region -- the one over the eastern and southeastern Gulf and another over the southern Gulf and the Yucatan.  That pair could make for an interesting upcoming run of days.  For the time being, there is no real indication of significant tropical development from either of these two features, but anything that close to home at this time of the year bears watching.  The National Hurricane center (NHC) currently clumps the pair together into a single large area that they post with a 10% chance of tropical development over the next 48 hours.  (Of these two areas, we’re thinking that the more southern one has the better chance of spinning-up into something down the road.)

What we do expect are scattered-to-numerous showers and t-storms by Friday with rain likely for Saturday and Sunday; rain chances will be greater closer to the coast on all three days.  We’re going with a 40% rain chance for Baton Rouge on Friday, with rain chances in the 60% to 70% range for Saturday and Sunday.  Don’t be surprised to see rain accumulations of 1” to 2” or more along and north of the I-10/12 corridor by the end of the weekend, with totals running as much as 2” to 4” with locally-higher totals closer to the coast.

We’ll carry “scattered” rains into the first half of the work week too.

Relatively Nice Again on Wednesday

By Jay Grymes & Steve Caparotta

Once again we enjoyed a nice “dry” air mass today with dew point temps running in the 60°s all day long -- compare that to dew points in the low to mid 70°s, closer to the long-term norm for July.  True, we had some high- and middle-level clouds throughout much of the day, but even with afternoon temps getting up to near 90° it didn’t feel bad at all for the middle of the year in South Louisiana (or SW Mississippi).

It looks like these dew points in the 60°s will linger for another day or so before the low-level air starts to really “moisten up.”  Plan on another morning on Wednesday will sun-up temps in the upper 60°s for the Red Stick under a few early morning clouds.  Partly cloudy skies will return for Wednesday afternoon with highs up around 90° -- and we’ll introduce a slight chance (20%) for hit-or-miss showers for Wednesday afternoon.

For now we’re also staying with just a 20% rain chance for Thursday afternoon and early evening -- so most of those Independence Day BBQs should stay dry.  What’s more, just about all of the rain should be gone before Thursday evening fireworks commence, so plan on enjoying your July 4th if you’ve got the day off.

By Friday, however, we’ll be changing things up.

An easterly wave moving west-northwest from the southeastern Gulf will be the key ingredient for a central Gulf Coast wet spell that begins Friday and continues through the weekend -- and possibly into early next week.  For the time being we don’t anticipate anything “tropical” (depression or storm) developing with this mess, but it still could prove to be quite the rain-maker, especially for the coastal parishes.  And while winds should remain well-below tropical-depression intensities, plan on a windy weekend, especially along and near the coastal parishes.

For now, we’re keeping decent rain chances in the forecast for Monday and Tuesday too.

Enjoying the Reduced Humidity!

By Jay Grymes & Steve Caparotta

A quasi-stationary front continues to linger along and near the Louisiana coast, but we’re enjoying the benefits of being on the north side of the boundary and that means a little relief from the normal summer humidity. Dew point temperatures have been in the 60°s at Metro Airport since late Sunday morning, even dipping into the very comfortable low 60°s around lunchtime today. And those lower dew points mean below-normal morning temps, with many WAFB neighborhoods starting out in the mid to upper 60°s on Monday morning.

And we’ll enjoy a bit more of the “drier” air, with dew points expected to remain in the 60°s into Thursday. Tuesday morning should start off quite comfortable by July standards for WAFB country, with wake-up temps in the mid to upper 60°s under mainly clear skies. Like we saw today, we could see some mid- to high-level clouds on Tuesday afternoon, so we’ll post a “fair to partly cloudy” forecast for Tuesday afternoon with highs in the upper 80°s to near 90°. Still, with the afternoon dew points in the 60°s, it won’t feel like a typical July day in the Red Stick.

Now understand: even with the “drier” air we expect into Thursday, that doesn’t mean “no rain” until then. But it does suggest that rain chances will remain on the low side, at least through Wednesday and into early Thursday. We’ll call for rain chances at 20% or less for Wednesday and set those chances at 30% to possibly 40% for Thursday afternoon with highs both days at or just above 90°.

There are two main drivers for this “drier” air: a huge upper-level ridge over the western U.S. and a persistent upper low centered over the middle Mississippi Valley. These two features are combining to produce a steady northerly and northwesterly flow of low-humidity air into the lower Mississippi Valley. The western U.S. ridge continues to generate record highs across much of that part of the country, but it’s the upper low over that mid-Mississippi Valley that is the real oddity. We don’t normally see such features in the middle of summer and the current thinking is that it will hang around until Wednesday before finally exiting to the north-northeast.

By Thursday -- July 4th -- we expect a return to something more typical for July rain probabilities, with rain chances for Independence Day posted at around 30% to 40%. Although we can’t rule out a lingering shower or storm by “Fireworks on the Levee” time this Thursday evening, we think that most of the showers and storms should be out of the way soon after sunset. 

After that, rain chances rising rapidly as we go into Friday and the weekend. In fact, for the time being we’re calling for “rain likely” for all three days.

The same rains that will make for a wet weekend locally will also mean a less than ideal 4th of July weekend for many of our Gulf Coast beaches. Showers and t-storms are likely each day from Wednesday through Friday along the Alabama and Florida beaches.

And finally ... the tropics remain fairly quiet. While there is an area of convection in the eastern Gulf, it shows no serious potential for developing at this time. However, given that it’s right outside the “back door,” we’ll keep a watch on it. Elsewhere, there are no other areas in the Atlantic Basin with any immediate potential for organization.