Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
335 PM EDT Sat May 28 2022
 
Day 2
Valid 12Z Sun May 29 2022 - 12Z Mon May 30 2022 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE CENTRAL/NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

An amplifying mid-level closed low will drop into the 
Intermountain West Sunday, leaving divergent downstream flow 
across the Plains with embedded shortwaves lifting northeast 
around the periphery of this trough. As this low deepens, it will 
also drive a strengthening jet streak into the Plains, with 
attended LFQ diffluence aiding to enhance deep layer ascent. To 
the east of the closed low, a cold front will be driven slowly 
eastward via height falls, moving from the Northern High Plains 
into the Upper Mississippi Valley through the day and into the 
night. 850mb flow gradually backing to the S and increasing to 
20-40 kts ahead of this front will drive impressive moist 
advection noted by PWs progged to reach +2 sigma coincident with 
MUCape climbing towards 2000 J/kg. The overlap of the strong lift 
and favorable thermodynamics will allow for scattered to 
widespread thunderstorms to develop on Sunday.

While there remains some uncertainty into the coverage of 
convection, there is likely to be at least a few rounds of storms 
moving SW to NE ahead of, and along, the cold front as multiple 
impulses embedded within the flow surge northward. The mean 0-6km 
mean wind is forecast to be quick at 30-40 kts from the SW, but 
unidirectional flow and propagation vectors aligned to the front 
suggest an enhanced training potential. With rain rates likely 
exceeding 1"/hr within the stronger convection, some places could 
receive as much as 3" of rainfall. While antecedent conditions are 
somewhat inhibiting to flash flooding due to drier than normal 
soils from a lack of recent rainfall, the inherited MRGL risk will 
remain with only cosmetic changes to account for recent guidance, 
since any repeating storms could produce a few instances of flash 
flooding.


Weiss
 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt