FOUS30 KWBC 242014
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Thu Oct 24 2024

Day 1
Valid 16Z Thu Oct 24 2024 - 12Z Fri Oct 25 2024

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

...16z update...
Very little change in initial reasoning. 12z forecast guidance
continues to denote a bimodal distribution of potential heavy
rainfall corridors across central IA into northern IL and/or
across northeast MO also toward northern IL with a quicker/eastward
shift of the intense rainfall rates capable to exceed short-term FFG
values. This includes an expansion into the Chicagoland region
where urban conditions further increase potential for limited
infiltration and high run-off capable of localized flooding.

Gallina


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

...2000 UTC Update...
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


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

...2000 UTC Update...
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN=
HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXHZTQJ8E$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN=
HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXxdBnVjY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN=
HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXqORX1oE$=20

=3D =3D =3D
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