616
FXUS63 KUNR 221720
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1120 AM MDT Tue Apr 22 2025

.KEY MESSAGES...

- Increasing chances for widespread precip across northeastern WY
  into western SD late Wednesday into Thursday.

- Active pattern will bring occasional precipitation chances
  through this weekend. A more substantial system expected to
  arrive towards the end of the weekend.

&&

.DISCUSSION...(Today Through Monday)
Issued at 320 AM MDT Tue Apr 22 2025

06z sfc analysis shows the cold front has pushed through South
Dakota. Upper air reanalysis depicts mostly westerly upper level
flow over the northern plains as an upper level wave sits to the
north. Said upper wave will pass to the north through today,
keeping the CWA under westerly, zonal flow aloft. Conditions will
be mild and dry today, though a few showers over the Black Hills
can`t be ruled out this afternoon.

Upper flow transitions from west to southwest through Wednesday
as an upper trough deepens over the west coast. Southerly flow at
the surface will advect ample gulf moisture into the central and
southern plains. While the bulk of the moisture will stay to the
south, enough will make it up to our neck of the woods to support
wide spread precip as midlevel FGEN takes place. In terms of how
much rain we`re going to get, deterministic runs are split into
three camps: GFS and NAM has band of strong midlevel FGEN across
northwestern SD Thursday morning, which would result in the
highest precip amounts being over northwestern SD into
southwestern ND; the Euro has band of decent midlevel FGEN across
south central SD earlier Wednesday night, which translates to
higher QPF over south central; and the Canadian splits the
difference and has strongest band of mid- level FGEN across
central SD Thursday morning. Most recent LREF still paints 50-80%
probs of at least 0.1" QPF over the majority of our CWA.
Probabilities for at least 0.25" QPF are highest over the Black
Hills into south central SD at 50-70%. The NBM paints 40-60% probs
of greater than 0.5" QPF over the northern and eastern Black
Hills and foothills. Colder air aloft pushes into the region
Wednesday night into Thursday, which will support snow in the
higher elevations of the Black Hills. Not anticipating much
accumulation, generally less than an inch.

Unsettled southwest flow continues through the end of the week
with conditions drying out somewhat Friday into Saturday (though a
couple of weak disturbances crossing through the region may
trigger a few showers Friday into Saturday). Cluster analysis
depicts deepening trough over the western US by late this weekend,
which will bring the next chances for widespread precip to the
region. It`s still a bit far out so confidence in exact impacts
remains low. However, LREF probs do show 40-60% chances for QPF
>0.1" over most of the CWA.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1119 AM MDT Tue Apr 22 2025

VFR conditions are expected through the forecast period. A shower
or two could develop across the Black Hills this afternoon.
Breezy westerly winds will develop across northwest SD this
afternoon.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...SE