Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Nov 20 2023 08:09:32

FOUS30 KWBC 200809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Mon Nov 20 2023

Day 1
Valid 12Z Mon Nov 20 2023 - 12Z Tue Nov 21 2023

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-SOUTH AND CENTRAL GULF COAST STATES...

Only minor changes were made to the Marginal Risk area from
yesterday's Day 2 ERO. Increasing upper-level difluence ahead of
the positively-tilted longwave trough will favor large-scale
ascent for widespread moderate-heavy rainfall, particularly across
parts of the Mid-South between the Bootheel of MO and the
ArkLaMiss where the ageostrophic circulation within the left-exit
region of the 130-150kt upper level jet will enhance the
divergence aloft/deep-layer ascent and southerly low-level
moisture transport. 850 mb moisture flux anomalies climb to around
3 standard deviations above normal late Monday-Monday night ahead
of the cold front, with the low-level response also allowing for
an uptick in deep-layer instability, even elevated instability
north of the triple point. The favorable dynamical and
thermodynamical setup within the Marginal Risk area (some
convective contribution with MUCAPEs ~500 J/Kg north and ~1000+
J/Kg south) should foster peak hourly rainfall rates between 1-2+
inches, especially Monday night where the uptick in the southerly
LLJ would favor increased upwind propagation and thus enhance the
risk for cell training. The CAM guidance is especially bullish
with the QPF along/near the track of the triple point (elongated
area of 2-3+ inches), given the overlap of favorable synoptic and
thermodynamic forcing. This would be from portions of AR into
northwest MS, the Bootheel of MO, and western TN.

Relatively low soil moisture currently within the top 40 cm (<25%,
which is below the 20th percentile for the entire outlook area),
along with the current FFG and relatively short duration of peak
low-level moisture transport and deep-layer instability, support
maintaining the Marginal Risk area with the expectation of a more
localized flash flood risk (especially in urban areas).

Hurley


Day 2

The Day 2 outlook will be updated by 0830Z.


Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!8JnLNwu5LRvAKNiip6FcsgErMNT9tWsZ4XawPheeDH5p=
SHbwFS_lQ1EnvK8YKOb81lcWgHbwHLYEH_H_5YhY5ewu5jM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!8JnLNwu5LRvAKNiip6FcsgErMNT9tWsZ4XawPheeDH5p=
SHbwFS_lQ1EnvK8YKOb81lcWgHbwHLYEH_H_5YhYU9RYwsY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!8JnLNwu5LRvAKNiip6FcsgErMNT9tWsZ4XawPheeDH5p=
SHbwFS_lQ1EnvK8YKOb81lcWgHbwHLYEH_H_5YhY3g92ccQ$=20


$$



=3D =3D =3D
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