964
AWUS01 KWNH 232204
FFGMPD
MNZ000-SDZ000-NDZ000-240400-

Mesoscale Precipitation Discussion 0310
NWS Weather Prediction Center College Park MD
603 PM EDT Thu May 23 2024

Areas affected...eastern South Dakota, far southeast North Dakota

Concerning...Heavy rainfall...Flash flooding possible

Valid 232202Z - 240400Z

Summary...Thunderstorms developing along a surface trough will
intensify through the evening. Supercells with rainfall rates
above 2"/hr are possible, which through training could produce
2-3" of rainfall with locally higher amounts. Flash flooding is
possible.

Discussion...An impressive line of convection has blossomed
rapidly along a surface trough analyzed by WPC moving east across
SD. Forcing for ascent is maximizing along this trough due to
impressive convergence as low level southerly flow emerging from
the Central Plains lifts into the boundary and an area of weaker
flow. At the same time, strong divergence downstream of a potent
closed mid-level low near the MT/WY border will continue to push
east, with the associated height falls and weakly coupled jet
streaks producing pronounced deep layer ascent. This large scale
lift will impinge into a thermodynamic environment that will
continue to destabilize on the 20-25 kts 850mb southerly flow,
with MUCAPE surging to around 3000 J/kg this evening overlapping
PWs as high of 1-1.2 inches, around the 90th percentile for the
date according to the SPC sounding climatology.

The slow eastward progression of the surface trough and other
associated synoptic features will allow for the intense ascent to
continue into the evening, interacting with the most impressive
thermodynamics from northern NE through eastern SD and into far
southeast ND where bulk shear of 40-50 kts will support organizd
clusters and supercells. Any supercells or organized clusters will
have rain rates that will likely exceed 1"/hr, and could briefly
eclipse 2"/hr according to HREF neighborhood probabilities and
HRRR 15-min rainfall accumulations. Despite the general eastward
motion of the surface trough, and the expected progressive nature
of individual cells on mean 0-6km winds of 30 kts, storms should
track generally parallel to the trough which should enhance the
training threat. Where these cells train, HREF probabilities
indicate a 10-20% chance for more than 3 inches in some areas,
especially across northeast SD/southeast ND where the trough
interacts with a stationary front.

40cm soil according to NASA SPoRT is above the 95th percentile
from north-central NE and across much of eastern SD. While there
is some uncertainty as to how far east these training cells will
track this evening before slowly weakening, there is at least
modest overlap of the CAMs and HREF probabilities with the higher
soil moisture. This is further reflected by HREF 3-hr FFG
exceedance probabilities reaching 15-20% atop compromised FFG
which is as low as 1.5"/3hrs, which suggests an increasing
potential for at least scattered flash flooding this evening.


Weiss

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...ABR...BIS...FGF...FSD...UNR...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON   47149745 46979681 46279680 45569719 44849763
            44179799 43689841 43369878 43159941 43060004
            43110049 44250055 46489924 46959829