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Excessive Rainfall Discussion
(Caution: Version displayed is not the latest version. - Issued 0651Z Mar 31, 2023)
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
251 AM EDT Fri Mar 31 2023

Day 1
Valid 12Z Fri Mar 31 2023 - 12Z Sat Apr 01 2023

A deep layer cyclone rapidly strengthens as it moves through Iowa
from Friday afternoon/evening and then weakens as it moves across
portions of WI and MI Friday night into Saturday. The relatively
swift progression of its attendant cold front would limit the
excessive rainfall potential over the northern OH Valley and
western Great Lakes.  Farther south, there will be a better chance
of cell training along outflow-generated effective fronts (as
mid-level capping across the region should be negligible to zero)
oriented quasi-parallel to the deep-layer west-southwest flow.
Where instability is plentiful and the dynamics are most
impressive, deep convection is expected to rapidly develop
probably around local noon with quasi-discrete supercells
initially expected to the preferred storm mode.  Some of the
strongest activity is anticipated to be across the Slight Risk
area, where hourly totals of 2-2.5" and local amounts of 3-5" are
possible (despite the recent downturn in QPF amounts across the
available guidance).  The evolution of the moisture field
indicates the possibility of two skirmishes of showers and
thunderstorms, which could lead to a longer duration heavy rain
threat overall.  Moisture Low-level moisture transport is expected
to be quite impressive, as a strong low-level jet (50-70 kts at
850 mb) ushers in precipitable water values of 1.2-1.8" (above the
90th percentile for the bulk of the MS/OH/TN Valleys).  Farther to
the north in the Midwest and Great Lakes region, hourly rain
totals will be less impressive (perhaps as high as 1.5" at times
Friday afternoon and evening), but the prolonged nature of the
rainfall may lead to some higher areal average totals (closer to
~2", though localized totals will likely be higher to the south). 
Farther south of the Slight Risk area (into portions of the Deep
South), flash flood guidance is generally higher, the dynamics of
the system are less impressive, and there's a greater chance for
mid-level capping when looking at 700 hPa temperatures.  The 00z
HREF and coordination with JKL and MRX led to some contraction of
the Slight and Marginal Risk areas across eastern KY and northeast
TN which appear to be relatively far removed from the best

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:
Day 2 threat area:
Day 3 threat area: