266
FXUS63 KUNR 261908
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
108 PM MDT Sat Apr 26 2025

.KEY MESSAGES...

-Strong low pressure will cross the region Sunday-Monday,
 bringing severe weather, widespread rains, and breezy winds

-Gradual warming trend after Monday with another chance for
 showers Wednesday

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 107 PM MDT Sat Apr 26 2025

Deep upper trough currently pushing into the Rockies today. This
system will eject out into the Plains Sunday, supporting a good
chance of thunderstorms by evening, some of which may be severe.
Breezy SE winds ongoing across the region today per ongoing sfc
pressure falls. Clearing has ensued from the BH west and north,
with mix out expected to spread east on the SD Plains as dry air
mixes down. Mainly dry tonight as SE flow persists. Clouds are
expected to spread back west overnight, as the BL cools and moist
upslope flow continues. Patchy fog will be possible, esp across
far western SD and part of northeast WY. Low pressure system will
shift east Sunday with the warm sector spreading over the region.
This will support very warm temps with highs in the 70s and 80s,
warmest on the SD Plains. Prefrontal trough will support
thunderstorm chances in the late afternoon/evening with severe
weather possible as sufficient CAPE and bulk layer shear will be
in place. Models have shunted the deeper moisture west some, which
puts the main area of TS development and track from SW SD into
central SD. TS/SHRA could also develop on the BH in the afternoon,
but there is some question on how deep ll moisture will be there.
Expect an MCS to develop and push NE across the SD Plains Sunday
evening with large hail and damaging winds the main threat. Plenty
of gulf moisture will then wrap into this system, which will
favor a good setup for appreciable rains Monday as the deformation
zones slides SE into the region. Expect the highest rain totals
will be in the northern BH and foothills given upslope
enhancement, with QPF values over an inch likely there. Some snow
will also be possible above 6kft in the BH, with some light accums
possible Monday. Things dry out some the remainder of next week
with additional chances for showers Wed as another impulse
traverses the flow. Expect a warming trend as well, peaking by
next weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1132 AM MDT Sat Apr 26 2025

Conditions will improve across the western half today as drier
air mixes down, with MVFR cigs expected toward central SD. Mainly
VFR conds expected tonight, although moist SE flow will allow the
potential for low clouds and fog across southwest SD late,
including the KRAP terminal.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 5 PM MDT this afternoon for SDZ001-002-012-
     013-078.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...JC
AVIATION...JC