Spearfish, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

450
FXUS63 KUNR 301120
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
520 AM MDT Fri May 30 2025

.KEY MESSAGES...

- Weak shortwave late today may produce an isolated thunderstorm
- Upper/thermal ridge peaks Sunday with summery temperatures
- Upper trough brings cold front Monday with active storms
  possible, especially east of the Black Hills
- Unsettled weather continues the rest of next week

&&

.DISCUSSION...(Today Through Thursday)
Issued at 217 AM MDT Fri May 30 2025

08z surface analysis had ridge from the southern plains into the
eastern Dakotas and cold front from central MT into NV. Water
vapour loop had shortwave ridge nosing into the CWA with compact
shortwave trough over central MT. GeoColor satellite loop late
Thursday afternoon showed smoke impinging on the CWA, which
matched HRRR smoke guidance, but not much nearby surface smoke per
surface observations. Main short term forecast concern is MT
disturbance and surface smoke potential.

Today/tonight, shortwave trough squashes shortwave ridge as it
scoots across the Dakotas, which is further east than previous
guidance. It will drag cold front (with brief gusty winds per
Bufkit soundings) through the CWA late this afternoon/early this
evening with mean SBCAPE around 500J/kg pooling along it. MLCIN
decent, so shortwave and front will have to work hard to create
convection. CAMs have a smattering of echoes over western SD.
Have introduced low PoPs to account. Shear is weak. Temperatures
will be near guidance.

Upper ridge builds into the northern Plains for the weekend. As
surface high sinks south of the CWA, a period of northeasterly low
level flow is forecast to bring surface smoke to the northeastern
third of the CWA (per HRRR smoke guidance). Added to forecast
Saturday afternoon to account. Thermal ridge peaks Sunday (MaxT
well into the 80s) after slightly cooler temperatures Saturday
(compared to today). Weak shortwave Sunday night will support low
PoPs as it propels surface trough into the CWA.

Monday/Tuesday, upper trough moves across the northern Plains
pushing a cold front into the area Monday. Frontal timing will
play a role in severe potential (1-2KJ/kg SBCAPE, but better bulk
shear may lag) for late Monday. Latest ensemble guidance features
a faster moving front, which is particularly shown by the 00z
ECMWF ensemble forecast. This scenario also pushes best chance for
>0.50" QPF (30-50% over entire CWA per NBM, 40-60% over south-
central SD per ECMWF ensemble) further southeast. Confidence
fairly low in QPF details, but high for cooler temperatures behind
the front Monday and all locations Tuesday.

Unsettled weather continues the rest of the next week as
progressive west/northwest flow drives a series of boundaries
through the northern Plains.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 519 AM MDT Fri May 30 2025

VFR conditions are expected through the TAF period. Isolated -tsra
are possible over western SD late this afternoon/evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Helgeson