102
AWUS01 KWNH 241718
FFGMPD
NEZ000-SDZ000-COZ000-WYZ000-242300-

Mesoscale Precipitation Discussion 0309
NWS Weather Prediction Center College Park MD
118 PM EDT Sat May 24 2025

Areas affected...Portions of the Central High Plains

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

Valid 241717Z - 242300Z

Summary...Increasing coverage of showers and thunderstorms will
spread across portions of the Central High Plains through this
evening. Rainfall rates of 1+"/hr are possible at times, leading
to rainfall of 1-2" with locally higher amounts where repeating
cells occur. This may lead to instances of flash flooding.

Discussion...The GOES-E visible satellite imagery this aftn
depicts slow clearing of the low-overcast, resulting in a surge of
increasing surface instability noted via the SPC RAP mesoanalysis.
Within this destabilizing environment, updrafts are forming and
strengthening as noted in the day-cloud phase RGB, and showers
have begun to develop across eastern WY. This fresh convection is
blossoming within a moistening column, aided by both upper level
SW flow (clearly evident as well in the visible imagery) and
underlying low-level SE flow which is pushing PWs to 0.7 to 0.9
inches, above the 75th percentile according to the SPC sounding
climatology. Embedded within the mid/upr SW flow, a shortwave is
noted lifting across central WY, and this feature will enhance
convective coverage into the afternoon, producing scattered to
widespread showers and thunderstorms across the area.

There may be two distinct modes of convection this aftn, but both
have the potential to produce heavy rain rates. Across the
Panhandle of Nebraska and much of SE Wyoming, the low-level
upslope flow will provide the impetus for development. Storms in
this vicinity will be generally slow moving as the low-level flow
and upper level flow counteract, with storms forming along terrain
boundaries, outflow boundaries, and differential heating
boundaries, leading to potential backbuilding and training. The
HREF rainfall rate probabilities for 1"/hr within this region peak
above 25%, and this is supported by HRRR 15-min rainfall as much
as 0.25-0.5 inches, so locally heavy rain with slower storm
motions could produce 1-2" of rain with locally higher amounts in
this area. Although soils are generally dry here as noted via NASA
SPoRT observations, this could still result in isolated instances
of flash flooding through the aftn.

Farther to the north, the primary mechanism for development will
be the progression of the embedded shortwave lifting into
central/northern WY. The high-res CAMs are in good agreement that
convection will become widespread as this forcing moves into the
increasingly favorable thermodynamics. Storms here will likely
organize in response to 30-45 kts of bulk shear, leading to
clusters and possibly repeating rounds of rainfall with rates up
to 1"/hr. FFG across South Dakota and northern Wyoming is lower,
generally 1-1.5"/3hrs, for which both the HREF and REFS suggest
has a 10-20% chance of being exceeded. While convection across
this area will likely be moving more progressively to the east,
isolated instances of flash flooding could still result.


Weiss

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

ATTN...WFO...BOU...CYS...LBF...RIW...UNR...

ATTN...RFC...KRF...NWC...

LAT...LON   44450414 44120356 43770277 43580233 43010212
            42660230 42430259 42000269 41250327 40980445
            41080553 42090618 43110598 44120570 44430506