Gillette, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

558
FXUS63 KUNR 191123
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
523 AM MDT Sat Jul 19 2025

.KEY MESSAGES...

- Slight chance (level 2 of 5) for severe thunderstorms from
  about 2-10pm this afternoon and evening
- Daily chances for at least isolated thunderstorms, some of
  which may be strong to severe, are expected Sunday into next
  week
- Near/somewhat above seasonable temperatures through next week

&&

.DISCUSSION...(Today Through Friday)
Issued at 148 AM MDT Sat Jul 19 2025

07z surface analysis had weak high over the upper Midwest and
weak trough from central MT into northeastern CO. Water vapour
loop had westerly flow over the northern plains with subtle
shortwave over central WY, which was assisting weak elevated
convection over the CWA per KUDX radar loop. Another upstream
shortwave noted over northern NV/UT, which will be the main
weather maker today.

This morning, initial shortwave slowly pushes eastward taking
elevated convection with it. Behind it, expect some stratus/fog
and weak subsidence which could complicate convective initiation
this afternoon. Secondary shortwave shifts into the CWA by tonight
as weak surface low develops over northeastern WY. Sustained
southeasterly flow (gusty at times) will promote the development
of 1-2KJ/kg SBCAPE by mid-afternoon from southeast MT into western
NE. 40-50kt 0-6km bulk shear will provide sufficient shear for
discrete supercells if SBCIN is overcome and secondary shortwave
arrives close to peak heating. Convergence ahead of WY surface
low, potential differential heating, and terrain should be
enough to break the cap. Subjective pattern recognition suggests
an active late afternoon/evening with very large hail possible
given forecast soundings. CAMs are a bit more subdued than
expected given setup, but CSU MLP a bit more bullish. SPC Day 1
slight risk has hatched area for very large (2"+) hail. PWATs
125-150% of normal, so locally heavy rain may occur. Stout
thunderstorms should wane after sunset as they push eastward.
Assuming solar insolation breaks out in earnest this afternoon,
guidance temperatures look fine.

Sunday, drier air filters into the western half of the CWA in the
wake of tonight`s shortwave. Best buoyancy shifts to northwest/
south-central SD. Weakly rising heights suggest thunderstorm
coverage will drop off, but isolated severe thunderstorms still
possible given 1.5-2.5KJ/kg SBCAPE and 30-35kt 0-6km bulk shear.
Temperatures will be near guidance.

Next week will be summery as large scale upper ridge from the
southwest CONUS to eastern seaboard becomes established. This puts
CWA in zonal/southwest flow which equates to periodic shortwaves,
frontal intrusions, and near/slightly above seasonal temperatures.
Typical late July weather.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 520 AM MDT Sat Jul 19 2025

Leftover shra/TS over the area will wane this morning. Areas IFR
conditions due to stratus/fog east of the Black Hills this morning
will become VFR this afternoon. Strong/severe TSRA with gusty,
erratic winds and hail will develop in earnest after 20z creating
local IFR conditions. After 20/05z, IFR stratus will develop from
K2WX-KICR.

&&

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

$$

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