Thursday, September 18, 2014

Drier Air Arriving on Friday

By Jay Grymes & Steve Caparotta

- drier weather for Friday and the weekend
- a little cooler by the middle of next week
We started the day with clouds, patchy fog and spotty showers along the coast as expected, but the morning drive was rather uneventful weatherwise for most WAFB communities.  For the afternoon, our warm-and-moist Gulf air mass kept most of us under the clouds while we watched a broad (non-tropical) disturbance over Texas slide towards the southeast into south Louisiana.
That disturbance was running into a layer of somewhat drier air at the lower levels across the southern parishes, holding the afternoon rain potential in check for most of the viewing area.  However, as we get into the evening hours, we expect the disturbance to moisten the air sufficiently to generate some evening showers -- with a rumble or two of thunder possible as well.  What rains that do develop should generally fizzle out during the overnight hours.
We mentioned yesterday how difficult it has been to define the precise location and movement of a rather poorly-defined front that has been in play over the lower Mississippi Valley for the past few days.  That pesky boundary appears to be just about ready to slide southward and it likely dissipates as it does.  This should allow a drier (less humid) air mass to move over the WAFB viewing area - - just in time for the weekend.
We’ll keep spotty showers in the coastal forecast for the early morning hours and add in a little light, patchy fog for the Friday morning commute and bus-ride, but most of us start the day on the dry-side with sunrise temps for the Red Stick running around 70° or so.  Friday highs will edge up to around 90° for metro Baton Rouge under fair to partly-cloudy skies.  While we can’t say “absolutely rain-free” for Friday afternoon, we’ve got spotty showers at best for the afternoon and evening: great news for ‘Live After Five’ and high-school football fans!
The weekend remains mostly-dry as well, with rain chances at a very modest 10% to 20% for Saturday and Sunday.  Morning lows for both days will run in the upper 60°s to low 70°s across the viewing area with afternoon highs around 90°.  Dew points should generally stay in the 60°s for most WAFB communities through the weekend -- not quite “autumn-like” but still relatively comfortable by late summer standards.
It looks like the weather gets a bit more interesting next week.  Over the past few days we’ve been talking about a cool front arriving in the region during the early part of the week.  We’re still tweaking the timing of its arrival, but for now it scheduled for a Monday passage through our viewing area.  So two questions remain:
(1) Will it be a significant rainmaker? and (2) Will it deliver our first “touch of fall”?
As for being a rainmaker, the extended range guidance is a bit mixed, but early indications are that we can expect scattered rains, at most, as the front pushes through.  This is not uncommon with our fall fronts.  When dealing with often-stormy spring-season fronts, there is usually a big difference (a steep gradient) between temperatures and moisture content on either side of the front: warmer-and-moist Gulf air on the south side, much cooler-and-less-humid continental air on the north side.  During the fall, however, these temperature and moisture differences across the frontal boundary tend to be less pronounced.  The ‘weaker’ gradients across a fall front typically translate into less lifting energy … and it is the lifting energy that generates frontal thunderstorms.
So for now, we’ll go with rain chances running about 30% or so for Monday as the front cuts across the viewing area and continues south into the Gulf. 
You’ll see that we have isolated rains in the Tuesday and Wednesday forecast: that will largely depend on how far south the front moves.  We’ll fine-tune that outlook as we head into the weekend but our suspicion is that both days will be dry ones, at least for the northern half of the WAFB region.
And what about a “taste of fall” on the backside of the frontal passage?  More like a “tease” than a “taste”: you will notice a drop in humidity and the temperatures will drop a bit too, but don’t be thinking sweaters and blankets just yet!
In the tropics, we continue to track the Atlantic’s Edouard.  The current National Hurricane Center (NHC) forecast keeps Edouard “alive” into the weekend as he heads east into ever-cooler waters.  Residents of the Azore Islands will want to keep an eye on ‘him’ but Edouard’s days are numbered.  The NHC is also watching a tropical wave that is moving into the eastern Atlantic off the coast of Africa, but that disturbance is simply too far away for our concern.

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