182
FXUS63 KUNR 031124
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
524 AM MDT Fri May 3 2024

.KEY MESSAGES...

- Cool with showers today. Minor snow accumulations possible in
  the Black Hills.

- Warmer and windy this weekend

- Strong Storm system early next week with potential for several
  hazards; severe thunderstorms Monday, locally heavy rain
  Monday/Tuesday (northeastern Wyoming/northwestern South Dakota),
  high winds Tuesday/Wednesday, snow for the Black Hills
  Tuesday/Wednesday.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 240 AM MDT Fri May 3 2024

Current surface map places low across northwestern Minnesota
with cold front across eastern South Dakota into northern
Nebraska. Water vapor shows shortwave over eastern Montana and
another over southern Idaho. The pair of shortwaves track eastward
today. Best lift occurs later this morning through early evening
over southern half of the forecast area along low level baroclinic
zone. Thermal profiles support snow in the Black Hills. High
resolution models point to accumulating snow for the higher
elevations with HREF mean around 3" (10:1 SLR) and the 25th-75th
percentile is 1"-5". Given expected snowfall rates (<0.5"/hour)
and time of day, SLR`s should be 25-50% lower. That still gives an
inch or two of snow accumulation which should mainly be limited
to grassy/elevated surfaces.

Surface high drops across the area early Saturday with dry weather
expected. As the high shifts east during the day southerly flow
increases. Shortwave ridge aloft crosses the area early Sunday as
deep low tracks through the Great Basin. Tight pressure gradient
will result in windy conditions Sunday. Highs warm into the 60s
for Saturday and 70s on Sunday.

Upper low swings through the Rockies into the Northern Plains
Monday with low stalling out over Dakotas Tuesday. Low then slowly
drifts southeast on Wednesday. Decent agreement with deterministic
GFS/ECMWF/GEM, through there are some minor differences in the
details. Chance of showers/thunderstorms increase late
Sunday/Sunday night with an uptick in buoyancy/theta-e advection
on nose of low level jet. Looks to be widespread
showers/thunderstorms Monday as robust QG forcing lifts through
the area. Timing of best lift/buoyancy/shear could result in a
threat of severe thunderstorms Monday afternoon. Focus for
widespread rains will come as TROWAL wraps around the upper low
Monday night through Wednesday. At this time, the heaviest rains
appear to be north/northwest of the forecast area, though the LREF
paints 40-50% probability of >1.50" QPF for parts of northeastern
Wyoming into the northern Black Hills and northwestern South
Dakota. Even with the potential for locally heavy rain, threat of
any flooding is very low. Biggest issue with the storm will be
very strong west-northwest winds. Will likely see gusts of 50-60
mph, especially on the plains north and east of the Black Hills.
Thermal profiles marginally cold enough that there could be some
snow in the northern Black Hills Tuesday/Wednesday. However there
is a wide spread in low level temperatures resulting in low
confidence in any snowfall amounts. LREF has small area in the
higher elevations with 30-60% probability of >6".

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 522 AM MDT Fri May 3 2024

MVFR/local IFR conditions expected in rain/snow today, across
parts of northeastern WY and SW to south central SD. Conditions
will gradually improve to VFR from west to east this evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...7
AVIATION...Pojorlie