933
FXUS63 KUNR 272303
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
503 PM MDT Thu Mar 27 2025

.KEY MESSAGES...

- Critical fire weather conditions continue through the evening
  hours across northeastern Wyoming.

- Mild and dry Friday with continued elevated fire weather
  conditions.

- Widespread precipitation expected Friday night through Sunday
  night, although uncertainty remains on exact snow amounts.
  Snowfall totals will depend upon temperatures and snowfall
  rates.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 221 PM MDT Thu Mar 27 2025

Upper level analysis shows dry westerly flow aloft over the forecast
area. Water vapor imagery depicts a stout upper low off the
Pacific Coast as an expansive plume of upper level moisture spreads
across the the Rockies. Southwesterly upper level flow
dominates across the western third of the US with multiple
shortwaves embedded within the flow from the North/Central Rockies
southwestward into CA. A surface stationary front is analyzed from
southwestern MT through western SD into northern NE; temperatures
west of this boundary are in the 60s to low 70s with 50s to low 60s
along and east of the boundary. Developing surface low pressure is
centered over east-central MT and is forecast to sag southeastward
through the overnight hours, shifting winds northwesterly near
daybreak.

Friday will be mild despite the cool front pushing through early in
the morning, with temperatures in the mid 60s to near 80F (50s in
the Black Hills). Gusty northwesterly winds are expected with the
frontal passage, increasing after 5-7am, with gusts up to 40 mph
through the afternoon. Mild temperatures, gusty winds, and low
relative humidity (bottoming out around 20% Friday afternoon) will
result in another day of elevated fire weather conditions across
northeastern WY and western SD.

Attention then turns to potential for widespread precipitation late
Friday night through Sunday. Initial shortwave trough will lift out
of the SW US overnight Friday into Saturday morning with broad upper
level ascent overspreading the Northern Plains. An additional
shortwave trough will follow approximately 12-18 hours later. While
finer mesoscale details will become clearer as we draw closer,
NBM/ensembles show fairly decent agreement in widespread
precipitation across the area with most areas likely to see at least
0.1" of QPF (~80%+) and slightly lesser, although still favorable,
chances of >0.25" (65-80%), and >0.5" (~50-60%). Some hints at a
faster progression of the system and drier air filtering in Saturday
are factors that could limit precipitation amounts, particularly
north of I-90 toward the ND/SD border.

The current snowfall forecast is on the lower end of the distribution
for the plains, although significant uncertainty remains. While
synoptic lift is certain, the uncertainties regarding this system
largely revolve around three primary, intertwined factors: the
low-level thermal profiles, snowfall rates, and diurnal effects.
Precipitation is expected to begin as all rain late Friday given
warm temperatures. Should low-level cold air advection and dynamic
cooling work to cool the low-level thermal profiles faster the
currently modeled, the chance of accumulating snow would be greater
across the plains. Also, with a large majority of the precipitation
falling during the day Saturday, snow will be fighting against the
stronger late March insolation. Finally, should snowfall rates be
high enough to overcome melting, would expect a better chance of
measurable snow across the plains and lower elevations.

Cluster analysis and ensemble guidance show unsettled flow through
much of next week. Despite the broad agreement in overall cyclonic
flow across the western half of the US, exact details remain very
uncertain with wide spread/low confidence in precipitation potential
and temperatures.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 503 PM MDT Thu Mar 27 2025

VFR conditions are expected through the period. A cold front will
cross the area Friday morning, bringing gusty northwest winds.

&&

.FIRE WEATHER...
Issued At 221 PM MDT Thu Mar 27 2025

Expect critical fire weather conditions this afternoon over
northeastern WY. Highs in the 70s, minimum relative humidity
around 15 percent, and southwesterly wind gusts around 30 mph are
expected. Additionally, very dry/well-mixed boundary layer
(unstable low levels) with some mid-level moisture may result in
spotty virga showers during the afternoon, primarily across
northeastern Wyoming. Confidence is low in the development of
virga, however, should any develop, gusty, erratic winds are
expected. Elevated fire weather conditions are expected elsewhere
this afternoon, persisting through Friday.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Red Flag Warning until 6 PM MDT this evening for WYZ314>317.
&&

$$

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