Thursday, May 3, 2012

By Jay Grymes & Steve Caparotta

We’re still getting a few “late” rain reports following Wednesday’s deluge.  On Wednesday evening we noted the rainfall bull’s eyes over central Tangipahoa and eastern Livingston parishes, but from what we’ve seen, the core of heaviest rains stretched across northcentral and northeastern Ascension Parish (the greater Prairieville area) and eastward into western Livingston Parish. 
Doppler Radar estimated rainfall for Wednesday. While the locations of the heaviest rains are accurately depicted, note that the radar was underestimating rain amounts, by several inches in some instances.
Widespread totals in that area ranged from more than 5” to at least one reliable report in excess of 8”, with one caller claiming a whopping 13.5” of rain!  With most of that rain falling in a three to six hour period, the storm event works out to be something on the order of roughly a “once-in-50-years” rainstorm based on 6” to 8” range of totals.  (If the 13.5” is real, that would rank as something beyond a “1-in-100-year” rain!)

If there is any good luck to be considered, it would have to be that the weather preceding Wednesday’s “mega-rain” had been relatively dry through the prior 12 days or so.  Had the days leading up to the mega-rain bee a bit more typically in terms of spring rains, Wednesday’s dousing would have led to even greater property damage!
A drier and warmer weather pattern will set-in for the coming days, as the disturbance that fueled Wednesday’s rains slowly drifts farther to the east (and north) while an upper-level ridge takes hold over the nation’s Southeast.  In fact, we could see some highs at or above 90° for Friday and into the weekend! 
While upper-air ridging will inhibit the development of afternoon showers and add to the mid-afternoon warm-up, we’ll keep the “return flow” (inflow of Gulf moisture) running continuously through the next 7 days.  While we’re not expecting any significant rain until the middle of next week (at the earliest), Gulf humidity will certainly be in place with dewpoints in the upper 60°s to low 70°s.  That will mean warm-and-muggy mornings, with patchy sunrise fog likely just about every day. 
And with highs climbing to around 90° and dewpoints near 70° over the next several days, that will translate into mid- to late-afternoon Heat Index values in the mid 90°s -- truly summer-like!

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