FOUS30 KWBC 070820
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Sat Dec 7 2024

Day 1
Valid 12Z Sat Dec 07 2024 - 12Z Sun Dec 08 2024

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

Churchill


Day 2
Valid 12Z Sun Dec 08 2024 - 12Z Mon Dec 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20
THE CENTRAL GULF COAST...

The Slight Risk has been maintained along and near the central=20
Gulf Coast for Sunday and Sunday night, confined to where more=20
appreciable deep-layer instability exists to support a higher=20
probability of more intense short-term rainfall rates (2"+/hr).
Still, this is considered a lower-end Slight Risk (based on the
wide 15-40% probability spectrum), suggesting widely scattered=20
instances of flash flooding at best (given expected localized=20
totals of 2-4" are near the corresponding 3-hr FFGs of 3-4").=20
Also, much of the Slight Risk area, particularly from Jasper TX=20
east-northeast to Alexandria LA, have received heavy rainfall over
recent days, and as a result the antecedent soil conditions and=20
streamflows are a bit higher compared to areas farther north (where
NASA SPoRT-LIS 0-100 cm soil moisture in the bottom 10th percentile
for much of MS/AR/LA). In addition to drier antecedent conditions=20
farther north and east across the Mid-South, very limited elevated
instability (MU CAPE ~200 J/kg at best) should prevent rainfall=20
rates from climbing too high (generally 1.5"/hr or less, driven by=20
impressive forcing via the shortwave and associated jet dynamics).=20
This suggests that a Marginal Risk should suffice with any flash=20
flooding being highly localized, despite areal average rainfall=20
amounts near 2" (expected to be spread out over 6+ hours).

Churchill/Hurley


Day 3
Valid 12Z Mon Dec 09 2024 - 12Z Tue Dec 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE=20
CENTRAL GULF COAST...

The shortwave trough responsible for heavy rainfall on Sunday over
much of the Lower MS Valley looks to eject northeastward into the
central Appalachians and Mid-Atlantic on Monday, bringing largely=20
beneficial rainfall (with totals generally under 1") to much of the
Northeast. Farther south along the central Gulf Coast, there are=20
hints of another (weaker) shortwave trough within the southern=20
stream that may enhance heavy rainfall along a trailing cold front.
Given the slowing of the front, the opportunity for training areas
of heavy rainfall will be greater on Day 3, best depicted by the=20
00z ECMWF and ECENS (depicting localized banded totals of 2-5" and=20
probabilities for 2" exceedance as high as 30%). This risk appears=20
greatest from southeast LA to southern AL and the tip of the FL=20
Panhandle, though the EC model system is the most extreme and=20
farthest east of all the models. Maintained the inherited Slight=20
Risk area with some adjustments, limiting the eastern extent a bit=20
given the lack of agreement from the other models. Uncertainty is=20
still relatively high, but subsequent outlooks should get a better=20
handle on things as these details begin to enter the CAM period.

Churchill


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD=
WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjhqpkS5o$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD=
WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjusUbWkU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD=
WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjb60vDRg$=20

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to
https://lists.illinois.edu and use the "Unsubscribe" link.  Otherwise email
Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.20-Linux