244
AWUS01 KWNH 282138
FFGMPD
SDZ000-NDZ000-MTZ000-WYZ000-290336-

Mesoscale Precipitation Discussion 1387
NWS Weather Prediction Center College Park MD
537 PM EDT Mon Sep 28 2026

Areas affected...Northern Black Hills to North-Central South
Dakota

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

Valid 282136Z - 290336Z

SUMMARY...Scattered thunderstorms north of the Black Hills should
continue to develop and track east over northwest South Dakota
though this evening. Slow movement and repeating cells should
continue to allow localized rates of 2"/hr as coverage increases.
Flash flooding is possible.

DISCUSSION...As of 2130Z...Scattered thunderstorms just north of
the Black Hills have developed in the warm sector ahead of a cold
front moving in from MT. Instability has increased from earlier
sunshine over northwest SD with SBCAPE now around 2000 J/kg.
Gulf-sourced moisture increases to the east as well with PW of
1.4" over north-central SD to 1" on the WY border where elevation
is higher. Warm sector activity should increase in coverage and
deep layer SWly flow should enable repeating cells and upwind
propagation. Despite ongoing drought conditions, localized flash
flooding is possible where the heavier cells repeat the most which
should generally be north of Rapid City and into north-central SD.

Recent HRRR and are behind on the ongoing activity but agree on
development east from there with a risk for 1-3" through 03Z. This
activity should shift farther east by late this evening as the
cold front advances through the discussion area.

Jackson

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

ATTN...WFO...ABR...BIS...BYZ...UNR...

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

LAT...LON   46220156 44910104 44260305 44030459 44250489
            44940425 45350381 46000311