653
FXUS63 KUNR 091809
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1209 PM MDT Tue Jun 9 2026

.KEY MESSAGES...

- Slight to enhanced (level 2-3 out of 5) risk of severe
  thunderstorms this afternoon and early evening east of the Black
  Hills from about 09/20z to 10/03z. All hazards possible
  (60-80mph wind gusts, 2"+ hail, isolated tornado).
- Critical fire weather conditions through early this evening
  over northeastern WY.
- Elevated to near-critical fire weather conditions Wednesday and
  Friday afternoon over northeastern WY/southwestern SD due to
  very dry air.
- Unsettled weather through the weekend per a series of fronts
  with up/down temperatures trending coolish for the weekend.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 1201 PM MDT Tue Jun 9 2026

18z surface analysis had low over southwest ND with a wavy
stationary front into MN, a dry-line into the Black Hills, and a
cold front into southwest WY. Gusty southeast winds ahead of dry-
line per 3-5mb/3hr pressure falls in ND. Morning water vapour
loop/0.5km visible imagery showed a distinct MCV moving from
central NE to eastern SD early this afternoon. Widening our view,
upper trough over the northwest CONUS with embedded
jetlet/shortwave over WY heading our way. Effects of these
features the main forecast concern.

Latest ensemble guidance indicate shortwave will lift northeast
this afternoon with attendant increase in mid-level flow
overtopping dryline. 2-3KJ/kg mean MUCAPE per SPC HREF pools
ahead of dryline with weakening MLCIN. Preliminary look at 18z
KUNR sounding shows the MLCIN well, in an otherwise deeply mixed-
sounding with steep lapse rates to 500mb. Effective shear
forecast to increase to 35-45kts. Most CAMS suggest convective
initiation between 09/19-21z over northwestern SD nearest the dry-
line/stationary front interface. Convection should zipper
south/south-east through the late afternoon/early evening hours,
moving east/northeast. Any discrete storms have the potential for
very large hail and isolated tornadoes. Right now, main mode looks
to be linear with potential for signficant wind gusts given 1800
DCAPE and CAM wind gust output for the eastern half of the CWA.
Best conditions for supercells develop east/north of CWA this
evening. Confidence in thunderstorms is high, but how they
evolve/strengthen will be dependent on where the boundaries are
in relationship to upper forcing given lower confidence to severe
weather evolution.

Colder air filters into the area tonight with noticeably cooler
weather for Tuesday along with some shra/TS per cyclonic flow/very
weak buoyancy.

Rest of the forecast looks unsettled as a series of disturbances
traverse the northern plains per northwest flow aloft. Deeper
trough brings higher PoPs/cooler temperatures for the weekend.
Each front/disturbance will bring gusty winds.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1118 AM MDT Tue Jun 9 2026

VFR conditions are expected at the TAF sites throughout the
forecast period.

Showers and thunderstorms are expected this afternoon (mainly
western SD) and will push eastward through the evening. MVFR/IFR
conditions and gusty, erratic winds are possible with any storms.

Gusty southwesterly winds early this afternoon will swing to the
west and northwest this evening, diminishing tonight.

&&

.FIRE WEATHER...
Issued At 1201 PM MDT Tue Jun 9 2026

Critical fire weather conditions will continue through this
evening over northeastern Wyoming. Minimum relative humidities
will drop to 10-20% with southwest winds of 20 to 30 mph, gusting
up to 45 mph. Storms will be high-based and capable of gusty,
erratic winds and lightning. These storms will have little
precipitation. Red Flag warning continues. Fuels are greener of
western SD, so no headlines continue.

The rest of the week will be unsettled as a series of fronts move
through, each containing gusty winds and variable temperatures.
Elevated to near-critical fire weather conditions are expected
Wednesday and Friday due to very dry air (teens minimum relative
humidity over northeastern Wyoming and southwestern South Dakota).

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Red Flag Warning until 8 PM MDT this evening for WYZ314-315-317.
&&

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Dye
FIRE WEATHER...Helgeson