Tuesday, June 11, 2013

More Heat, Less Rain Ahead

The upper-level ridge over the west-central U.S. continues to slowly ease its way to the east, increasing the strength of the “cap” over Louisiana. Remember, by a “cap or “lid,” we are referring to high pressure in the mid- to upper-levels of the atmosphere. This cap not only suppresses cloud development (and therefore inhibits rainfall), but also promotes sinking air. Sinking air must warm as it descends, so the sinking process actually adds heat to the lower-levels of the atmosphere.
We’ll stay warmer-than-normal and mainly dry through the rest of the week. Red Stick residents should plan on muggy mornings with patchy fog and sunrise temps in the low to mid 70°s while afternoon highs under mostly-sunny to partly-cloudy skies reach the mid 90°s.
These won’t be record afternoon temps but still take care in the heat, especially when under the direct sunshine. Remember, the mid-day sunshine can add as much as 10° or more to the “feel” of the air ... and that’s before we consider the Heat index impact of our traditional summertime humidity.
Now, okay ... a handful of you will still see a passing afternoon shower just about every afternoon this week. Even as the upper-level ridge sets-up right over top of us towards mid-week, there are still going to be a couple of pop-up places where the rising air punches high enough through the upper-level cap and produce a localized shower. The Gulf air mass at the surface is obviously very warm and very moist, and warm-and-moist air is, by definition, unstable and quick to rise.
Think of it like this: with the abundance of low-level unstable air, some fraction of it is going to find a “weakness” in the overhead cap. Almost like the fork holes your mom puts in her pie crust to let some of the steam out while it bakes. So yes, we could see a couple of blips on the Titan9 radar just about every afternoon this week, but they will be few and far between for the next few days.
We’re watching the potential for a “backdoor” cool front to slip southward and try to make it to the Gulf Coast on Friday. Signals are a bit mixed at this point, but given the time of year, the odds of the front pushing into and through the WAFB viewing area are on the low side. Still, the front could get close enough to put a crack in the atmospheric cap, and the closer the front gets the better the potential rain chances on Friday afternoon.
For now, I’m thinking that the front won’t make it this far south and only gets close enough to increase rain chances to about 20% for Friday afternoon. Not much of a big deal, really, and that would still be rain chances lower than normal for this time of year. Of course, we’ll keep an eye on the forecast developments with this scenario over the coming days.
Another day passes and we remain quiet in the tropics.

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