FOUS30 KWBC 040815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Sat Jan 4 2025

Day 1
Valid 12Z Sat Jan 04 2025 - 12Z Sun Jan 05 2025

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

Churchill


Day 2
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 will develop over the central US 
into Day 2, originating from a potent shortwave trough currently
digging into the Four Corners region. The trough is expected to
cut-off into an upper-low as it emerges into the central/southern
Plains with strong DPVA interacts with the right-entrance region 
of a broad phased jet structure (~130 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, ushering in highly 
anomalous tropospheric moisture (for this time of year) with 
precipitable water values nearing 1.5" (near the 90th percentile to
max moving average, per JAN/BNA/BMX sounding climatology). While 
downscaled global guidance (GFS/ECMWF) continues to suggest only 
localized 1-2" totals, the impressive dynamics of this system 
(along with the anomalous moisture) suggest the potential for this 
guidance to locally be exceeded (as the 00z FV3 suggests, but 
additional CAMs should better capture the even with the upcoming 
12z runs). That said, both the progressive nature of the 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 reaches 500-2000 J/kg) are expected limit localized 
totals to the 2-3" range (with as much as 1-2" in an hour with the 
main line of convection). Have maintained the inherited Marginal 
risk area for much of the Southeast (with some additional expansion
towards the southwest, where instability will be most abundant) 
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 3
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

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