Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1132 AM EDT Tue Apr 23 2024

Day 1
Valid 16Z Tue Apr 23 2024 - 12Z Wed Apr 24 2024

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

Otto

Day 2
Valid 12Z Wed Apr 24 2024 - 12Z Thu Apr 25 2024

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

...In and near OK...
Guidance continues to show an area of convective development
across central and eastern OK within a low- level convergence field
associated with a stalled boundary over the southern Plains north
of the Red River. The atmosphere is expected to be uncapped, based
on 700 hPa temperatures forecast. Modest instability located over
the region due to active return flow regime will aid in the
convective pattern and create an environment capable of low- end
flash flooding concerns, especially within any training cells
within the confines of the stalled front. All guidance, to some
degree has a QPF maximum between north- central OK over into the
Lower Mississippi Valley. Spread within the model guidance remains
high, both in placement and magnitude; the 00z ECMWF remains the
wettest. The overall synoptic pattern of precipitable water values
approaching 1.5", CAPE of 1000-2000 J/kg, and enough 850 hPa
inflow/effective bulk shear to support organized convection. Hourly
rain totals to 2" with local amounts to 4" are possible within
this environment. Higher FFG indices/drier soils are in place over
many of the areas that could receive heavy rainfall. The general
model trend has been slightly northward, away from the more
sensitive soils caused by recent heavy rainfall near the Red River
of the South. Considering the setup, once the guidance shows better
convergence, a Marginal Risk could be in the offing.

Roth


Day 3
Valid 12Z Thu Apr 25 2024 - 12Z Fri Apr 26 2024

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
THE PLAINS AND MIDWEST...

Strengthening moisture flux across the Plains and Midwest ahead of
a low pressure system is expected to raise the precipitable water
values to 1.5"+. Inflow at 850 hPa is forecast towards 60 kts,
with effective bulk shear to match. A broad area of 1000-3000 J/kg
of CAPE is forecast by SREF guidance. Temperatures at 700 hPa
suggest a relatively uncapped atmosphere. The above ingredients
support mesocyclone formation, which can be producers of heavy
rainfall, moreso where cells align, despite what should be quick
cell motion. Cell training is possible as the deep layer flow is
out of the south-southwest. The guidance has a stronger signal for
heavy rainfall somewhere between the southern Plains, Mississippi
Valley, and the Midwest Thursday and Thursday night than advertised
the previous day, but agreement is lacking on location which is
keeping the WPC QPF magnitude modest. Like the previous day, the
00z ECMWF is the wettest with a signal over 9" near the KS/OK
border. As heavy rainfall is expected of some magnitude across
portions of OK and AR on Wednesday and Wednesday night, expanded
the Marginal Risk southward from continuity to cover those areas.
Should the guidance converge on location, a Slight Risk upgrade
would be possible as we get closer to the event. Hourly rainfall to
2.5" with local amounts to 5" are expected, which would be most
impactful in urban areas and areas with saturating soils between
now and Thursday.

Roth


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt