588
FXUS63 KUNR 201737
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1137 AM MDT Mon May 20 2024

.KEY MESSAGES...

- Widespread showers/isolated thunderstorms today/tonight.

- Potential for light snow accumulations for higher elevations of
  the Black Hills tonight.

- Active pattern continues through Memorial Day holiday weekend.


&&

.DISCUSSION...(Today Through Sunday)
Issued at 212 AM MDT Mon May 20 2024

Current surface map places low across northeastern South Dakota
with cold front into the southern Nebraska Panhandle. Water vapor
shows upper trough over the Rockies/Great Basin with southwest
flow over the forecast area. Showers expected to increase across
the area later this morning into early afternoon with robust
850-600mb frontogenesis associated with a period of enhanced
upper divergence. Highest rainfall amounts set up from central
Wyoming into the Black Hills area. HREF precipitation is showing
80-100% probability of >0.25" around the Black Hills and a 30-50%
probability of 0.50". Frontogenesis wanes this evening as
shortwave moves through the central Rockies. The shortwave tracks
through Nebraska Tuesday, with surface low deepening over
Minnesota. Northern portion of deformation zone will bring
widespread showers/thunderstorms over south central South Dakota
tonight through Tuesday morning with rainfall amounts of
0.50"-1.00". Showers continue over the rest of the area as
secondary impulse rotates through eastern Wyoming/western South
Dakota. Thermal profiles show lowering of web bulb temperatures
tonight, with transition to snow for the higher elevations of the
Black Hills. Some snow accumulation is possible, mainly above 5000
ft msl. HREF probability of accumulated snowfall (assuming 10:1
SLR) shows 80-100% probability of >1" and 40-60% of >3" for areas
above 6000ft msl.

Active pattern continues through the weekend with a daily chance
of showers/thunderstorms. A weak impulse crosses the area
Wednesday with a few showers. There is a better chance of
showers/thunderstorms on late Thursday into Friday and again late
into Friday followed by another late Saturday into
Sunday.Saturday into Sunday as stronger shortwaves swing through
the area.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1135 AM MDT Mon May 20 2024

Showers will increase in coverage through afternoon. Chances for
precip will be highest south of Interstate 90. MVFR/IFR
conditions are expected in showers and more widespread cigs
tonight...especially across northeast Wyoming, the Black Hills,
and southwest South Dakota.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...7
AVIATION...Dye