948
FXUS63 KUNR 301722
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1122 AM MDT Thu Jul 30 2026

.KEY MESSAGES...

- Marginal to slight (1-2 out of 5) risk of severe thunderstorms
  this afternoon/evening with the primary risk of damaging winds,
  but large hail may also occur
- After "cooler" temperatures today and Friday, very hot weather
  returns for the weekend with the hottest day Sunday
- Elevated (Saturday) to critical (Sunday) fire weather
  conditions expected this weekend

&&

.DISCUSSION...(This Afternoon Through Wednesday)
Issued at 1105 AM MDT Thu Jul 30 2026

16z surface analysis had weak low over the NE panhandle with a
boundary into central SD per 0.5km 1-minute visible satellite
loop. Cold front was located from western ND into western WY.
Water vapour loop had shortwave trough over northern WY with 80kt
jet streak. These features starting to force CU/TCU/TS along the
surface boundary with evidence of decent lift ahead of the
shortwave over northeastern WY/eastern MT. Concern this
afternoon/evening is severe weather.

This afternoon/evening, shortwave trough moves east as
convergence along the surface boundaries increase. Mid-level flow
increases effective shear to 25-35kts with locally higher amounts
over central SD. Strong buoyancy will develop this afternoon,
especially east of the Black Hills. Initial storm mode may be
cellular with large hail potential, but the trend will be toward
severe clusters/linear severe convection as storm cold pools
congeal. Primary threat will be damaging winds gusts (70+ mph).
Looking for a fairly early start this afternoon with CAMs focusing
on the central/southern Black Hills and central SD this afternoon
and then Lemmon to Winner by evening as the main shortwave wraps
through the CWA. PWATs will be 150-200% of normal east of the
Black Hills, so locally heavy rain and potential flash flooding
may occur. Activity wanes overnight. Temperatures will be near
guidance.

A weak shortwave moves through Friday, but drier air will be
filtering into the CWA, so PoPs should be limited to our higher
terrain areas.

Hot to very hot weather returns for the weekend with the
preponderance of ensemble guidance giving highs near 110F for some
folks Sunday. Much drier air in place, so thunderstorm chances
will be unmentionable. Cooler weather returns Monday with actual
"cool" air in place for the middle of next week per flattening
upper ridge and west/northwest flow aloft for the northern Plains.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1121 AM MDT Thu Jul 30 2026

Showers and thunderstorms will continue to develop early this
afternoon across northeast Wyoming, the Black Hills, and south-
central South Dakota. MVFR/IFR will be possible near any storms,
along with gusty, erratic winds even some distance from the
storms. Storms will end from west to east through the afternoon
and evening hours. A cold front crossing the area today will bring
breezy northerly winds through the afternoon. Conditions are
expected to improve after 31/10Z.

&&

.FIRE WEATHER...
Issued At 1105 AM MDT Thu Jul 30 2026

Strong/severe thunderstorms are expected this afternoon/evening
with strong gusty, erratic winds as the primary threat. Elevated
(Saturday) to critical (Sunday) fire weather conditions are
expected this weekend. Minimum relative humidity will drop into
the upper single digits/teens Saturday in the west and Sunday over
much of the area. Winds Saturday will be marginally gusty for
critical Fire Weather, but should be more robust on Sunday per
very deep boundary layer mixing.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Schultz
FIRE WEATHER...Helgeson