879
FXUS63 KUNR 150849
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
249 AM MDT Tue Jul 15 2025

.KEY MESSAGES...

- Slight risk (2 out of 5) of severe thunderstorms this
  afternoon/early evening over small parts of south-central SD/
  northeastern WY
- Beneficial rainfall potential through Wednesday
- Unsettled and warmer for the end of the week into early next
  week

&&

.DISCUSSION...(Today Through Monday)
Issued at 242 AM MDT Tue Jul 15 2025

08z surface analysis had cold front along the ND/SD to WY/MT
border areas with outflow boundary racing to the SD/NE courtesy of
decaying convection over the northwest half of the CWA. Water
vapour loop had a couple of disturbances over the northern
Plains, but main trough slipping across the US/Canadian border in
the vicinity of ID/western MT. The cold front and upper trough
will be the main weather makes in the short term.

Today/tonight, cold front hangs up over south-central SD today as
upper trough drops into MT. SPC HREF depicts 1-2KJ/kg MUCAPE over
the southern half of the CWA in the afternoon, peaking at
2-3KJ/kg over south-central SD. 25-35kt 0-6km bulk shear
sufficient for severe thunderstorms. Wild card is post frontal low
clouds which may blanket the northern half of the CWA by midday.
If low clouds push further south, surface based convection chances
decrease markedly. Most CAMs indicate convective initiation over
south-central SD by early afternoon and then over the southern
Black Hills/northeastern WY later this afternoon. Main threats
large hail/damaging wind. Strongest convection wanes later this
evening as cold front pushes well south of the CWA. Temperatures
tricky, but feel northern half of CWA has highest probability
(50-80%) chance of low clouds, so have cut MaxTs to account. Left
the south along.

Wednesday, upper trough slips across the northern plains with
synoptic forcing/limited buoyancy combining to produce high PoPs
in a regime characterized by PWATs ~125% of normal. Beneficial QPF
likely (SPC HREF 50-80% >0.75" western half of CWA) for parts of
the CWA with convective elements focusing highest totals.
Temperatures will be quite cool for mid- July, some 15-25F below
normal.

Thursday through Monday, zonal flow propels a series of weak
disturbances across the US/Canadian border as thermal ridge slowly
expands into the northern Plains. Disturbed weather will continue
as temperatures recover to seasonal readings.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1055 PM MDT Mon Jul 14 2025

Showers and thunderstorms will continue overnight across
northeast WY and western SD, then moving into central SD in the
late morning. A cold front will cross the forecast area through
the day on Tuesday, bringing widespread MVFR/IFR CIGS. More storms
will develop late Tuesday into Tuesday evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...13