FOUS30 KWBC 230754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu May 23 2024

Day 1
Valid 12Z Thu May 23 2024 - 12Z Fri May 24 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE ARKLATEX
INTO THE MID-SOUTH...

...ArkLaTex into the Mid-South...
A stationary front is expected to stretched from northeast Texas/ 
southeast Oklahoma into Arkansas, while slowly weakening. Precipitable
water values expected to remain 1.5 to 2 standard deviations above the
mean along the boundary. Additional shortwave energy moving in from
the west across the Southern Plains will support additional 
convection in this high moisture axis and there is potential for 
additional heavy rains from northeast Texas/southeast Oklahoma, 
east across the Lower Arkansas Valley into the Lower Mississippi 
Valley. The stationary front weakens and southerly low level flow 
pushes the high PW values farther to the north. Hourly rain totals
to 2.5" and local amounts to 5" are possible. While some model
spread continues, convergence seen in the 00z Canadian Regional, 
00z UKMET, and 00z ECMWF in the Slight Risk area led to some 
increased confidence, despite the weaker look in the 00z HREF 
probabilities and more bifurcated 00z GFS solution in this region.
The Slight Risk remains and has shown some expansion equally due 
to the heavy rainfall which occurred Wednesday and because of 
future heavy rainfall concerns Thursday and Thursday night.


...Northern Plains/Upper Midwest...
The marginal risk area across eastern portions of the Northern to 
Central Plains into the Upper Mississippi Valley remains. 
Additional convection is likely ahead of the next strong area of 
height falls/cooling aloft rotating from the Northern Rockies into
the region. This area has seen heavy rainfall amounts as of late, 
keeping stream flows high.  The strong upper trof, and associated
strengthening low level southerly flow and increasing PW values, 
there will be potential for localized heavy rainfall amounts that 
may fall across areas that received heavy totals over the past 24 
hours.

Roth


Day 2
Valid 12Z Fri May 24 2024 - 12Z Sat May 25 2024

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS ACROSS THE
ARKLATEX, MISSISSIPPI VALLEY, & SOUTHERN APPALACHIANS..

...Upper Mississippi Valley into the Upper Great Lakes...
The next strong area of height falls moving into the northern High Plains
will continue to push eastward through the Northern Plains and into the
Upper Mississippi Valley. The overall favorable large scale conditions
ahead of these height falls from Thursday will continue into Friday
along the associated front where strong frontal convergence in an axis
of PW values 1 to 1.5 standard deviations above the mean will support
potential for moderate to locally heavy rainfall totals. This front
does look progressive, which may limit very heavy amounts. The marginal
risk was drawn to where there may be overlap of locally heavy rains
Friday through Friday night with heavy rains that have fallen as of
late. Hourly rain totals to 2" and local amounts to 4" are expected
where cells merge or manage to train.


...ArkLaTex, Tennessee Valley, & southern Appalachians... 
A broad marginal risk area continues and was expanded in areal
coverage from continuity based on the most recent QPF guidance and
to some degree heavy rainfall that occurred near the ArkLaTex on
Wednesday. Precipitable water values across these regions will 
remain above average, with additional shortwaves in from the west 
supporting scattered convection and locally heavy rainfall amounts.
Spread remains within the guidance, which keeps the threat level 
Marginal. The ingredients in place support hourly rain totals to 
2.5" with local amounts to 5". Should the guidance show more 
convergence in future runs, a Slight Risk could be prudent as 
portions of the area saw heavy rainfall Wednesday and should see 
heavy rains again on Thursday.

Roth


Day 3
Valid 12Z Sat May 25 2024 - 12Z Sun May 26 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS NEAR THE MISSOURI/ 
KANSAS BORDER...

The Marginal Risk in the area continues and was expanded in areal
coverage to account for the most recent QPF guidance, with the
Slight Risk a new addition. A cyclone emerging into the central 
Plains will bring precipitable water values of 1.5"+ across the 
region on the heels of sufficiently strong low level 
inflow/effective bulk shear. The region lies within a general 
instability gradient, with CAPE expected to rise to 4000+ J/kg 
within an increasingly capped atmosphere across the southern 
Plains. Pockets of moderate to heavy rainfall are forecast within 
this region. There is increasing overlap in the QPF pattern near
the KS/MO border within the 00z guidance where three hourly flash 
flood guidance is modest, so went ahead with an upgrade to a Slight
Risk for this update. However, given the ingredients, hourly rain 
totals to 2.5" with local amounts to 5" are possible where 
mesocyclones form and/or cells manage to train.

Roth

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