600
AWUS01 KWNH 200207
FFGMPD
NEZ000-SDZ000-MTZ000-WYZ000-200805-

Mesoscale Precipitation Discussion 1337
NWS Weather Prediction Center College Park MD
1005 PM EDT Sat Sep 19 2026

Areas affected...Central and Eastern WY...Far Southeast
MT...Western SD...NE Panhandle

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

Valid 200205Z - 200805Z

SUMMARY...Heavy showers and thunderstorms developing and expanding
in coverage across portions of the High Plains and the Black Hills
may result in some areas of flash flooding going through the
overnight hours.

DISCUSSION...An ejecting upper-level trough from the northern
Rockies will be overspreading portions of the High Plains
overnight, and this will bring clusters of heavy showers and
thunderstorms to areas of central and eastern WY, far southeast
MT, western SD, and the NE Panhandle region. This will include the
Black Hills.

The energy will be favoring an area of low pressure across eastern
WY which will help to enhance the low-level convergence across the
region and especially near portions of the Black Hills where radar
imagery already shows some locally organized clusters of strong
convection. MUCAPE values ahead of this surface low center are on
the order of 500 to 1000 J/kg, and there is plenty of moisture in
place for heavy rainfall rates with PWs running upwards of 2 to 3
standard deviations above normal.

The 18Z HREF/REFS consensus suggests an uptick in convective
organization over the next several hours across areas of eastern
WY and near the SD/NE border region as strong DPVA associated with
the upper trough ejects across these areas. Some rainfall rates of
1 to 2 inches/hour, with some localized 2 to 4 inch rainfall
totals will be possible overnight. The HREF/REFS consensus
suggests some probabilities locally as high as 50 to 70 percent
for seeing the 3-hour FFG values exceeded.

Therefore, given the guidance and the current radar and satellite
trends, some areas of flash flooding will be possible. The threat
may extend as far north as southeast MT, but generally the
heaviest rainfall is expected to be across eastern WY and in close
proximity to the Black Hills with areas as far south as the
northwest part of the NE Panhandle potentially seeing some of
these heavier rains and impacts as well.

Orrison

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

ATTN...WFO...BYZ...CYS...LBF...RIW...UNR...

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

LAT...LON   45440370 45040296 44100252 42970252 42230291
            41870391 41950495 42440636 42440822 42810928
            43380933 43950730 44630595 45310484