427
FXUS63 KUNR 132250
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
450 PM MDT Tue May 13 2025

.KEY MESSAGES...

- Marginal risk of severe thunderstorms tonight over northeastern
  WY/far western SD
- Slight risk of severe thunderstorms over south-central SD
  Wednesday afternoon
- Very windy Thursday
- Precipitation chances tonight through Thursday night, with
  higher chances early next week

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 217 PM MDT Tue May 13 2025

Latest upper level analysis shows a broad trough over the Rockies
with some mid-level moisture streaming northward from Wyoming and
western Nebraska. At the surface, the cold front continues to
slowly move east, but the southern push has stalled close to the
SD/NE border with the eastern edge just east of a Midland to
Martin line. Ahead of the front, the warm and windy conditions
continue with highs in the 90s and southerly winds gusting to
35-40 mph. Behind the front, temperatures are in the 60s and 70s
with breezy northwest winds gusting to 40-45 mph.

For later this afternoon, some of the CAMS hint at possible
convection developing along the cold front. Latest visible
satellite shows some CU forming. Shear is weak in this area and
the CAP is strong, but with 500-1000 J/KG ML CAPE, it`s possible a
storm could develop. Thus have kept low pops in the forecast.

For tonight, the upper level trough will move east, with
strengthening southerly mid-level flow across the Northern Plains.
The cold front will stall parallel to the upper flow aloft. Deep
layer shear combined with weak elevated buoyancy may result in some
scattered showers and storms developing and moving into the forecast
area around 02Z and continuing through 10Z or so. Veering of the
wind profile with moderate mid-level northwesterly flow aloft
supports elongated hodographs in the post-frontal air, creating
the potential for isolated elevated supercells. The primary hazard
will be hail, but some strong/severe wind gusts could be possible
closer to the front. The main area of concern for stronger/isolated
severe storms will be where the marginal risk has been posted
over far western SD and northeast WY.

On Wednesday, the cold front will stall a little and perhaps
retrograde a bit in response to the surface low deepening over the
eastern Dakotas. The upper ridge pushes eastward with most of the
synoptically driven QPF now well northwest of the forecast area.
Ahead of the cold front, persistent southerly and southeasterly
winds will push moisture into the area. Sufficient shear and SB CAPE
will be in place to support a slight risk of severe thunderstorms
from mid-afternoon to early evening across south-central South
Dakota. The stubborn cold front will finally move east of the CWA
Wednesday night.

For Thursday, the surface low will continue to deepen over eastern
North Dakota, creating a tight pressure gradient over the CWA. NBM
depicts a 95% chance of 45 mph wind gusts across the western SD
plains, with probs of 40-60% for winds greater than 60 mph. Thus,
future wind headlines appear likely for the usual northwest-wind
windy areas on the SD plains. As for precipitation, a few showers
will be possible mainly over the northern areas (NBN probs now
less than 50%), but amounts will be minimal - maybe a couple of
hundredths.

Northwest flow will become more zonal Friday through Sunday as an
upper ridge develops over the Rockies while the the next trough
moves onshore over the western CONUS. A few weak shortwaves embedded
in the flow may allow for low pops through the weekend with
temperatures remaining slightly below normal. Models are showing
the longwave Pacific trough closing off with nice southwest flow
developing over the Western High Plains and Northern Plains later
this weekend. It is still too far out to project the exact track
of this system, but it could bring beneficial QPF to the entire
forecast area and possibly some snow to the higher elevations.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 446 PM MDT Tue May 13 2025

Showers and thunderstorms will move into northeastern WY this
evening, spreading into western SD overnight. Gusty, erratic winds
and brief MVFR conditions will be possible near showers/storms.
Behind the storms, MVFR/IFR ceilings will move into northeastern
WY early Wednesday morning, which will dissipate by early
afternoon. Another round of showers/storms will develop across
western SD Wednesday afternoon, with MVFR conditions and gusty
winds possible again. The greatest threat for strong winds and
hail will be across central SD and eastward.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Pojorlie