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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 1518 UTC Sun May 26, 2024
Valid: 16 UTC May 26, 2024 - 12 UTC May 27, 2024
Day 1 Excessive Rainfall Forecast
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1118 AM EDT Sun May 26 2024
Day 1
Valid 16Z Sun May 26 2024 - 12Z Mon May 27 2024


16Z Update...
Extended the Moderate Risk area westward across much of southern
Kentucky as several waves of heavy rainfall work their way eastward
through late morning and early afternoon...followed later today by
the potential for a second round of convection. The HREF
probabilities for 24 hr amounts in excess of 3 inches are in excess
of 45 pct across the outlook region with spotty coverage of
probability of 24 hour rainfall exceeding 5 inches embedded within
that area. These amounts are certainly reachable given some
observed values and MRMS depicted amounts that have exceeded 2.3
inches in under an hour. After a lull later today...high
resolution CAM guidance tends to be in pretty good agreement that
a new round of convection will develop over southeast Missouri or
western Kentucky that tracks eastwards...with a pretty good chance
of traversing at least some of the heavy rainfall footprint left
behind by the storms this morning (even though the placement of
storms in round 2 differs a bit from high res model to high res
model). This same area depicted by the expanded Moderate risk area
was highlighted by the National Water Model rapid onset graphic.
Elsewhere...changes tended to be made based on trends seen in mid-
to late-morning satellite and radar imagery.


...0830Z Excessive Rainfall Discussion...
A cyclone moving across the Midwest and Great Lakes is expected to
draw ample moisture (precipitable water values of 1.50-1.75"),
low-level inflow, effective bulk shear, and instability into
portions of the MS, TN, and OH valleys. A convective complex trying
to congeal near the KS/MO border at the present time is expected
to continue moving east to east- southeast across KY and portions
of TN this morning into this afternoon, near and to the north of an
old/weak segment of the polar front. Making matters worse, a
second convective round is expected Sunday evening moving from the
confluence of the OH/MS rivers east to east- southeast across the
same region as a cold front moves through. Rainfall over the past
week across portions of the TN/KY border is 300-600%, so soils
should be saturated. With the specter of hourly rain totals to
2.5", and local amounts of 6", an upgrade to a Moderate Risk was
necessary in this area, despite the 00z guidance spread. This
evolution is supported by the 00z HREF which was on the southern
portion of the guidance spread and since 700 hPa temperatures are
low enough to support a relatively uncapped atmosphere, a more
southern solution as advertised by the HREF makes sense
conceptually. A broad Slight Risk surrounds this region where
similar amounts are possible and soils are less saturated.
Mesocyclones, cell training, and cell mergers are the expected
reasons for excessive rainfall here.

While lower rainfall amounts generally are expected in the East and
the Upper Midwest, the expected low-level inflow, effective bulk
shear, and precipitable water values indicates that an isolated
excessive rainfall threat exists, with hourly rain totals to 2" and
local amounts to 4". The difference between the two regions are
the degree of soil saturation/recent rains and the available
instability. Much of WI has experienced 300-600% of their average
seven day rainfall so soils should be sensitive. However,
instability should be minimal so low- to mid-level frontogenesis
appears to be doing the heavy lifting, heavy rainfall production-
wise. Went ahead and raised a Slight Risk in and near portions of



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