Wednesday, July 9, 2014

More Rain on Thursday

By Jay Grymes & Steve Caparotta
First Alert QuickCast:
- rains tapering off later this evening, but keep the umbrella handy through the weekend
For the second day in a row, some “hot” thunderstorms generated very active cloud-to-ground lightning strikes during the afternoon.  Although not quite as energized as Tuesday’s systems, once again we watched a band of storms sag from north-to-south across the metro area.  Today’s storms arrived a little earlier in the afternoon -- good news for the Baton Rouge evening commute since the main action had cleared most of the Red Stick region before the 4 p.m. rush hour. 
As is typically the case in the summer, loss of daytime heating means that the area storms subside into the evening, although we will keep a very slight chance of showers in the forecast through the night, especially closer to the coast.  Metro area sun-up temperatures on Thursday will run in the low 70°s under mostly cloudy skies -- and like earlier this morning, we’ll anticipate a few morning showers along the coast again.  For the afternoon, it’s back to scattered showers and storms, as we seem to have locked into a repetitive daily pattern.  For Thursday, expect daytime highs for most WAFB neighborhoods to reach the upper 80°s to low 90°s.
Why so active?  Warm and moist Gulf air is the major player.  As we’ve mentioned before, warm-and-moist air is unstable, which means it is ready and willing to rise.  In the simplest terms, any significant daytime heating adds to the instability – and the more unstable, the faster the air will rise.  As the moisture in the warm air rises it cools and condenses, forming clouds and raindrops.  The more lift, the more (and faster) that moisture is added to the developing clouds.
We’ve been getting a little extra help over the past couple of days thanks to upper-air disturbances tracking over the region.  These are low-pressure areas traveling in the mid to upper levels of the atmosphere that contain pools of cold air within them.  The extra-chilled air aloft helps get the low-level unstable air rising even more quickly and in greater amounts.  Plus the sub-freezing air at higher elevations encourages hail and lightning development.  The result: thunderstorm outbreaks like we’ve had the past couple of days.
Once a round of storms rolls through the area, it tends to use up the available storm energy and temporarily stabilizes the local atmosphere.  However, if the day’s storms go by early enough in the day and the sun breaks out again and re-heats the air, you can get a second outbreak going.  Fortunately between yesterday and today, storms were late enough in the afternoon and the cloud deck lingered long enough that there was no opportunity for a Round #2.
All in all, our forecast stays fairly consistent right into and through the weekend: morning lows in the low to mid 70°s, afternoon highs in the upper 80°s to low 90°s, and scattered mainly-afternoon showers and t-storms each day.  Although rain chances for Thursday may be a tad higher at 50% or so, set those chances at 30% to 40% for the rest of the week and the weekend.
Still quiet in the tropics, with no real threats for development anywhere in the basin through the weekend.

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