Subj : HVYRAIN: Excessive Rainfa
To   : All
From : Mike Powell
Date : Thu Oct 24 2024 09:02:00

FOUS30 KWBC 240815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Thu Oct 24 2024

Day 1
Valid 12Z Thu Oct 24 2024 - 12Z Fri Oct 25 2024

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE MIDDLE MISSISSIPPI VALLEY...

Introduced a Marginal Risk for portions of the Middle MS Valley,
from northwest IL and southeast IA into northern MO (and adjacent 
portions of far northeast KS). Strengthening southwesterly low-
level flow (850 mb) to 40-50 kts this evening will usher in PWATs 
to near 1.25" (well above the 90th percentile, per SPC sounding 
climatology), along with sufficient instability (ML CAPE 1000+
J/kg) and forcing (potent shortwave trough crossing the Central
Plains) for convective development. Strong vertical shear (~50 
kts) with idealized curving hodographs will likely favor discrete 
convection (with both the mean flow and bunkers right vectors 
favoring storm motions of 20-30 kts), and despite relatively low 
PWs (particularly compared to warm season convection) any
supercells will likely be capable of 1-2"/hr rainfall rates (per 
40-km neighborhood HREF probabilities for 1"/1-hr exceedance of 
40-50%). While 1-2" totals should be well tolerated by soils (and 
largely beneficial, given dry antecedent conditions), localized 
training could result in too much rainfall (2"+) too quickly (in a 
matter of 2-3 hours). Given this threat, an isolated instance or 
two of flash flooding is possible. 

Churchill


Day 2
Valid 12Z Fri Oct 25 2024 - 12Z Sat Oct 26 2024

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

Churchill


Day 3
Valid 12Z Sat Oct 26 2024 - 12Z Sun Oct 27 2024

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

Churchill
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