Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Mon May 20 2024
Day 3
Valid 12Z Wed May 22 2024 - 12Z Thu May 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
OKLAHOMA, ACROSS THE LOWER ARKANSAS VALLEY INTO THE MID MISSISSIPPI
VALLEY...

...2030Z Update...

Adjustments to the threat areas this forecast cycle were to expand
the Slight and Marginal Risks areas farther south where greater
moisture content (up to 2" PWs) and instability (1,000-2,000 J/kg
MLCAPE) looks to be present. This setup also takes place beneath
unusually strong WSW 250-500mb mean winds aloft, along with an IVT
above the 90th climatological percentile that is intersecting the
aforementioned frontal boundary Wednesday afternoon and into
Wednesday night. With modeled soundings also depicting warm cloud
layers as deep as 12,000-13,000ft Wednesday afternoon, this setup
has a higher ceiling for potential flash flooding and will be
closely monitored in subsequent forecast cycles. For now, no
consideration of a Moderate Risk today given the lingering
uncertainty on QPF and the axis on where the heaviest amounts
occur.

Mullinax

---Previous Forecast---

The trailing frontal boundary from the low moving northeastward
from the Upper MS Valley into the Upper Lakes region day 2, will
slow significantly on the southern end from the Southern Plains
into the Lower Arkansas and Mid Mississippi Valley during day 3 as
it becomes aligned more parallel to the southwest flow aloft. PW
values expected to rise to 2+ standard deviations above the mean
along this slowing frontal zone, supporting potential for heavy
rainfall total from southeast Oklahoma, northeastward through the
Ozarks of Arkansas and Missouri and toward the Mid Mississippi and
Lower Ohio Valley regions. Shortwave energy embedded in the
southwest flow aloft will enhance uvvs in this anomalous PW axis
Wednesday afternoon continuing into the early hours of Thursday.
Training of cells parallel to the boundary is a concern for heavy
to locally excessive rainfall totals day 3 with the slight risk
drawn for the max qpf consensus and across regions where soil
moisture and stream flows are high. Changes to the previous outlook
were to narrow the slight risk area to better match current qpf
consensus and best region for potential training of precipitation
areas.


Oravec