FOUS30 KWBC 050815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Sun Jan 5 2025

Day 1
Valid 12Z Sun Jan 05 2025 - 12Z Mon Jan 06 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST AND CENTRAL GULF COAST...

An impressive deep layer cyclone is taking shape over the central 
US early this morning, originating from a potent shortwave trough 
digging through the Central Rockies over the past couple of days. 
The trough is in the process of cutting off into an upper-low as 
it emerges from the Rockies into the central Plains. Strong DPVA 
in association with the trough will interact with the right- 
entrance region of a broad phased jet structure (~140 kt jet 
streak @ 250 mb over the Mid-Atlantic, and a smaller ~100 kt jet 
streak near the Ozarks). A substantial low-level jet (850 mb of 
40-60 kts) is expected to form as a result of deep cyclogenesis,
stretching from the Central Gulf Coast to the Mid-South, ushering 
in highly anomalous tropospheric moisture (for this time of year) 
with precipitable water values nearing 1.5" (between the 90th 
percentile and max moving average, per JAN/BNA/BMX sounding 
climatology). Most hi-res CAMs continue to suggest localized 1-2" 
totals in association with combined totals from scattered 
convection in the open warm sector and the following primary squall
line in association with the approaching cold front, though a 
couple of solutions (FV3 and CMCreg) suggest localized streaks of 
2-3" totals (from northeast LA through north/central MS into 
northwest AL). While much of these totals may occur over a 
relatively short period (with any flash flooding conditions more 
likely due to storm mode and sub-hourly rates and totals of 1-2", 
00z HREF 40-km neighborhood probabilities for 2" exceedance over 3 
hours barely peak at 20-30%. Therefore the progressiveness of this 
system (and the limited window of time in the afternoon to take 
advantage of destabilization, with SB CAPE from east TX and 
southern LA to the Mid-South reaching 500-2000 J/kg) should largely
preclude any organized flash flood threat. Have maintained the 
inherited Marginal risk area once again, generally encompassing the
expected warm sector of the system (while excluding areas farther 
north where more impressive broad QPF exists, as this precipitation
will mostly occur in the form of ice and snow).

Churchill


Day 2
Valid 12Z Mon Jan 06 2025 - 12Z Tue Jan 07 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill


Day 3
Valid 12Z Tue Jan 07 2025 - 12Z Wed Jan 08 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill

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