Tuesday, August 12, 2014

Mainly Dry Through Friday

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- ‘cool’ front arrives overnight
- less humid for the next 2 to 3 days

The vast majority of us stayed dry today, yet the expected ‘cool’ front remains well to our north over northern and central Louisiana (as of 3pm). So we are still in the “warm” sector, still under the influence of our muggy Gulf air mass, and still waiting for a front to push through the region. 

Why no rain? Great question.

The fact is, we can’t entirely rule out a spotty shower or two this evening as the front draws closer ... but this event is not shaping up to be a textbook frontal passage. Here’s why: it seems as if the atmosphere is ‘drying out’ from the top down. In other words, the air at the mid- and upper-levels (1 to 5 miles up) is already rather dry compared to a normal summer day. Add-in a little subsidence (sinking) and the combination acts to suppress vertical cumulus-cloud development. To over-simplify: warm-and-dry air aloft is not allowing rainclouds to develop. 

With the front providing some low-level lift -- and given the daytime solar heating -- we shouldn’t be surprised by a couple of showers later today. We’re seeing that this afternoon along the front over parts of northeastern Louisiana and west-central Mississippi -- but when we say “a couple of showers” that’s exactly what we mean. Any showers that develop later today will be “spotty” at best.

The ‘cool’ front moves through the BR metro area overnight and through the pre-dawn hours Wednesday, arriving over the coastal parishes by Wednesday’s sunrise. The front then slowly continues to creep southward to the coastal waters through Wednesday and into Thursday before stalling and meandering close to the coast. With the front along and near the coast, we could see a few showers and even some t-storms along the coastal margin and over the coastal waters, but we think that the vast majority of WAFB communities stay dry from Wednesday through Friday. 

What’s more, the ‘continental air mass’ behind tonight’s front should deliver a nice drop in humidity, with dew points falling into the 60°s (“comfortable” on the summer dew point scale). Morning minimums for the Red Stick should slip into the upper 60°s for one or two mornings thanks to the reduced humidity and mainly-clear morning starts. Now make no mistake, the afternoons will still be hot with mostly-sunny to partly-cloudy skies and temperatures reaching the low 90°s, but the “drier” air (less humid) will be most welcomed.

We keep the BR metro area dry through Friday, although we expect the stalled front to begin a northward retreat as a warm front on Friday and into Saturday. By the weekend, our typical summertime heat-and-humidity will be back in place along with a return to our traditional afternoon scattered-rains regime. 

Nothing worth noting in the tropical Atlantic, according to the National Hurricane Center.

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