Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Dec 18 2022 00:51:14

FOUS30 KWBC 180051
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
750 PM EST Sat Dec 17 2022

Day 1
Valid 01Z Sun Dec 18 2022 - 12Z Sun Dec 18 2022

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

Chenard


Day 2
Valid 12Z Sun Dec 18 2022 - 12Z Mon Dec 19 2022

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

Campbell


Day 3
Valid 12Z Mon Dec 19 2022 - 12Z Tue Dec 20 2022

....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF STATES...

The latest guidance has trended incrementally higher along the
immediate coast across parts of southeast Texas and southern
Louisiana while maintaining a separate QPF swath maximum centered
over north-central Louisiana. WPC QPF increased amounts 0.25 to
0.75 inches for the southernmost Parishes of Louisiana which
raises the areal average QPF into the 1.50 to 2.70 range. Although
the best instability and moisture is likely to remain over the
Gulf during this period, there is a notable northward shift that
elevates the potential threat for isolated flash flooding from
southeast Texas to extreme southern Alabama and northern to
northern Louisiana and central Mississippi. Thus, a Marginal Risk
area was raised for this region.

Campbell

Previous discussion... Debated about the need for a Marginal Risk
area over portions of Louisiana where the models and the WPC
deterministic QPF have amounts at or above 1.75 inches.  Think the
threat for excessive rainfall is non-zero if there is enough
overlap between the heaviest amounts with areas that were doused
within the past few days.  However, a front over the northern Gulf
of Mexico suggests that any convection over Louisiana will be
elevated and not tapped into the best instability. There will be
the right entrance region of an upper jet providing support aloft
while the GFS and ECMWF strengthen southerly 850 mb flow into the
35 to 40 kt range over southern Louisiana for a period on Monday
....but precipitable water anomalies barely reach 1.25 standard
deviations above climatology.  As a result...refrained from
highlighting the risk of excessive rainfall.

Bann



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!67cCU060aQJ6QLS3VE6v4026yqHGkIlkXMsLxKnNTTYU=
XkZlHHFeKw3LFk8VWorjf13ffUYI3Ml0azlAhpAt0Y5WLi8$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!67cCU060aQJ6QLS3VE6v4026yqHGkIlkXMsLxKnNTTYU=
XkZlHHFeKw3LFk8VWorjf13ffUYI3Ml0azlAhpAtr9hw33A$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!67cCU060aQJ6QLS3VE6v4026yqHGkIlkXMsLxKnNTTYU=
XkZlHHFeKw3LFk8VWorjf13ffUYI3Ml0azlAhpAtxr9keT4$=20


$$



=3D =3D =3D
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