945
FXUS63 KUNR 240809
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
209 AM MDT Tue Jun 24 2025

.KEY MESSAGES...

- Marginal to slight risk (1-2 out of 5) of severe thunderstorms
  this afternoon/evening
- Unsettled Wednesday with a marginal risk (1 out of 5) of severe
  thunderstorms
- Much warmer Thursday through Saturday afternoon with lesser
  chances for thunderstorms

&&

.DISCUSSION...(Today Through Monday)
Issued at 206 AM MDT Tue Jun 24 2025

07z surface analysis had low pressure over western CO with trough
into western ND. Water vapour loop had mean trough from central
Canada into the southwest CONUS. Main wave spinning over southern
NV with a couple of wiggles heading toward the CWA. Modest low-
level jet (30kts per KUDX VAD wind profile), 800-700mb theta-e
advection, and 100-500J/kg MUCAPE creating isolated/scattered
shra/TS near the WY/MT-SD/ND border early this morning. Expect
this convection to bubble through sunrise, then tail off.
Attention then turns to severe weather potential today.

Today/tonight, NV upper low inches eastward shooting lead
shortwave into WY this afternoon/evening. Surface trough becomes
warm front as weak low develops along it in central WY. Return
flow along warm front pools 1-2KJ/kg SBCAPE by 21z. Convergence
along warm front combined with shortwave should be sufficient to
break cap with 50kts 0-6km bulk shear. Supercells most likely
initial convective mode with large/very large hail possible. CAMs
(per updraft tracks) seem to favor left-moving supercells over
northeastern WY and this is plausible given forecast hodographs.
Per orientation of convection to surface low and warm front
position, wouldn`t be surprised to see enhanced 0-1km shear, so
isolated tornado threat still present, but CAMs sure don`t seem
to emphasize right movers over northeastern WY. Storms should grow
into clusters this evening and track east/northeast overnight.
Significant MLCIN is forecast to be present on the SD plains, so
how far surface-based convection makes it into SD is suspect.
Temperatures today will be seasonal/near guidance.

Wednesday, upper low lifts northeast as it weakens into an upper
trough. Sustained southeasterly flow may thrust "semi-humid"
conditions into far western SD (50-80% chance Td>60F) which will
support modest buoyancy and sufficient shear for isolated
strong/severe thunderstorms. However, forcing
mechanism/organization is uncertain. Temperatures will be
seasonal/near guidance.

Thursday through Saturday afternoon, west/southwest flow aloft
will promote thermal ridge building into the northern plains and a
return to hot weather, especially Friday when MaxT pushes into
the mid 80s to upper 90s. TSRA chances much less, but not zero.
Saturday night into early next week, slightly unsettled weather
develops per northwest flow aloft and a series of weak fronts.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1053 PM MDT Mon Jun 23 2025

Mainly VFR conditions expected through the TAF period. Isolated
to scattered showers and thunderstorms are expected overnight with
local brief MVFR conditions possible. Given isolated nature of
storms, have not added TS to the terminals attm. Did add TS to
KGCC for Tues afternoon when better coverage is expected.

&&

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

$$

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