Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
852 PM EDT Wed Apr 24 2024
Day 1
Valid 01Z Thu Apr 25 2024 - 12Z Thu Apr 25 2024

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS IN AND NEAR EASTERN
OKLAHOMA AND WESTERN ARKANSAS...

01Z UTC update...
Realigned the orientation of the Marginal Risk area to better
match the low-level thetae gradient...with higher values advecting
northward across the western High Plains ahead of an approaching
shortwave trough and cooler/drier air feeding southward from strong
surface high pressure over the Great Lakes region into the
Mississippi Valley region. While there should be increasing
isentropic upglide overnight that leads to the development of
showers and thunderstorms...and a sufficient combination of CAPE on
the warm side of the low level front and increasing moisture over
the outlook area...localized rainfall amounts of 1 to 3 inch
amounts are possible but the latest HREF continued to be
unenthusiastic about the chances for 3 inch totals. Confidence
about the potential for excessive rainfall is lowest in the Kansas
portion of the outlook area given the dewpoint depressions...suggesting
that the threat may not develop until after the end of the Day 1
period at 12Z.

Bann


Previous discussion issued at 0700 UTC...
...OK/AR...
OK/AR will remain an area of diffluent 1000-500 hPa thickness just
east of a migrating mid- level ridge axis translating east from
the Four Corners region. At the surface, a front will lift north
Wednesday night into early Thursday in advance of the approaching
upper level trough from the Southwest. Mid-level capping should be
minimal based on the forecasted 700 hPa temperatures, under 9C.
Precipitable water values 1-2 sigmas above average for late April
-- 1.5-1.75" -- are forecast by the model consensus to be in place
near and just north of the surface front with elevated CAPE of
1000 to 2000 J/kg (higher to the south) may allow for stronger
cells capable of high rainfall rates. Effective bulk shear/low-
level inflow should increase to 35-40 kts. Non- traditional cell
training within a WNW steering flow near and poleward of the front
could allow for hourly totals to 2" and local 4" amounts. While
the 00Z HREF isn't sold on 3"+ amounts in the area, precipitable
water values in the area have trended upwards each day, and now
the 00z Canadian Regional, though at a smaller scale, supports the
wetter ECMWF solution. Went ahead and introduced a Marginal Risk
in this update.

Roth