Subj : HVYRAIN: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Nov 18 2023 15:16:11

FOUS30 KWBC 181516
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1015 AM EST Sat Nov 18 2023

Day 1
Valid 12Z Sat Nov 18 2023 - 12Z Sun Nov 19 2023

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

Gallina



Day 2
Valid 12Z Sun Nov 19 2023 - 12Z Mon Nov 20 2023

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

Bann


Day 3
Valid 12Z Mon Nov 20 2023 - 12Z Tue Nov 21 2023

....There is a Marginal Risk of Excessive Rainfall Over Portions of
the Lower Mississippi Valley and Gulf Coast States...

Flow aloft over the Lower Mississippi Valley and Gulf Coast region
will back in response to the amplification of a long wave trough
over the Intermountain region and the Rockies.  There should be
increasing divergence aloft...which sets the stage for
cyclogenesis over Arkansas or far southern Missouri during the
latter part of the day. Convection with some potential for
producing some flash flooding due to downpours is expected to
develop in an increasingly moist and unstable airmass along and
ahead of a cold front tied to the surface low.  The NCEP guidance
and the ECMWF show precipitable water values increasing to between
1.8 and 2.0 inches from Louisiana to parts of Arkansas and
Mississippi by 21/06Z and more than 2.5 standardize anomalies by
21/12Z. Those values approach 2 standardized anomalies above
climatology for this time of year.  The 18/00Z GFS and UKMET were
most aggressive with maximum 24-hour rainfall amounts in the 2
inch to 3 inch range while the ECMWF was only showing isolated
maximum amounts generally at or below 1.25 inches. Flash flood
guidance values generally range from 2.5 to 3.75 inches at both
the 1- and 3-hour time intervals...so it is possible that these
values could be challenged in localized areas if the rates are
sufficiently high.  However...lack of any GEFS or SREF members
showing 3 inch contours suggests not upgrading to a Slight risk at
this point.

Bann



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!9g9J1CxtmifNMS9MGKmpneVp8GS0O68m4pEb5q5mQsNj=
yi9Vr4wbvDQswtTKaZp1jfXyWlmtZrz_q_rZXOxLkpuy6zE$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!9g9J1CxtmifNMS9MGKmpneVp8GS0O68m4pEb5q5mQsNj=
yi9Vr4wbvDQswtTKaZp1jfXyWlmtZrz_q_rZXOxLDb6OR_E$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!9g9J1CxtmifNMS9MGKmpneVp8GS0O68m4pEb5q5mQsNj=
yi9Vr4wbvDQswtTKaZp1jfXyWlmtZrz_q_rZXOxLzqXaeWA$=20


$$



=3D =3D =3D
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