911
FXUS63 KUNR 032338
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
538 PM MDT Thu Apr 3 2025

.KEY MESSAGES...

- Chances for light rain and snow increase this evening through
  Friday afternoon.

- Below normal temperatures expected over the weekend, with a
  gradual warming over next week.

- Dry most of next week, with a couple chances for light
  precipitation the latter half.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 207 PM MDT Thu Apr 3 2025

Upper level models and Water Vapor show upper trough over the four
corners region, with a weaker disturbance in the northern flow
over MT. Sfc charts depict a surface front over MT running
northwest to southeast near our northern border, while a surface
low associated with the trough sits over CO. Radar shows some
potential light showers or virga near the boundary over
northwestern SD this afternoon.

Steeper lapse rates and some mild instability may lead to some
showers developing over the Black Hills this afternoon ahead of
the main precipitation this evening into Friday. Precipitation
increases this evening as theta-e adv allows for rain moving into
southwestern to south central SD. At the same time, frontal
boundary over MT moves into the region, increasing precipitation
chances from northeastern WY into northwestern SD. Over Friday
these two disturbances will converge to the east, leaving much of
our central CWA mostly dry. Much of the CWA can expect any
precipitation to start out as rain, transitioning to a rain/snow
mix early Friday morning, while the central and northern Black
Hills may see a start more as snow or a mix, before transitioning
to all snow. Generally light accumulations less than an inch are
expected over our forecast area outside of the Black Hills, where
the HREF probability of snow > 2" is in the 70 to 90 percent
range. Elsewhere is 0 to 10 percent. The higher elevation areas
could see accumulations up to 4 inches through Friday afternoon.
Following passage of the cold front Friday, deterministic models
show 2-4 mb/3hr press rises supporting strong north to northwest
winds in the morning and afternoon. Much of the western SD plains
will see near adv winds behind the front, however not enough
confidence for a wind headline at this time.

Forecast area drys out for the weekend following this disturbance,
with cooler than normal temperatures behind the front. Over the
weekend upper ridge builds over the west coast and gradually
slides eastward, supporting a warming trend for much of next week
back to seasonable and then above normal temperatures by next
weekend. Precipitation chances return middle of next week, as
deterministic models depict a weak wave crossing the northern
plains in the Tuesday/Wednesday timeframe.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 532 PM MDT Thu Apr 3 2025

Rain showers/MVFR conditions will increase across the area this
evening as a storm system approaches the region. A cold front will
cross the forecast area tonight, bringing a change to snow and IFR
conditions. NW winds behind the front may gust to 40kt at times.
VFR conditions will work back into the region during the day on
Friday as drier air moves in from the NW.

&&

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

$$

DISCUSSION/KEY MESSAGES...Dye
AVIATION...13