156
FXUS63 KUNR 211916
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
116 PM MDT Tue Jul 21 2026

.KEY MESSAGES...

- Cooler temperatures are still in store through Thursday.

- Much needed rainfall through mid-week for some, but not all.

- Hot and dry conditions to return for the upcoming weekend.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 113 PM MDT Tue Jul 21 2026

Latest water vapor imagery shows 500hpa ridge axis extending from
Pacific NW southeast to the Gulf. Desert SW monsoonal moisture is
streaming through NV/ID then into MT and the Dakotas. One weak
wave is located in southwest MT/northwest WY with another more
robust wave located in central NV. At the surface, Canadian high
pressure is nosing into the Dakotas with northeast to easterly
winds across our SD counties, and southeast winds across our WY
counties. At 17Z, temperatures across the CWA vary from around 70F
across the north, to the lower 80s across Campbell Co, WY and our
southwestern SD counties.

Aforementioned wave located in southwest MT will slide into the
CWA this evening/overnight while surface high pressure ridge drops
southeast becoming mainly located along the I-29 corridor of the
eastern Dakotas. Models continue to be bullish on pwat values,
with amounts running 150-175% of normal by 06Z Wednesday. The
probability of 1.50 or greater pwat values across much of the CWA
ranges from 50-90%, and for 1.75 or greater ranges from 30-40%
basically across our southern counties. The probability of seeing
0.25 of rainfall or greater from 06Z-12Z Wednesday is 40-50% and
stretches in a corridor from KGCC-KRAP-KICR. Will continue with
scattered to likely pops in the overnight period tonight for much
of the area.

There will be a brief dry spell from Wednesday morning through
early Wednesday evening as subsidence behind exiting wave clears
things out. Pwat values still remain high, and by 00Z Thursday
begin to push 200% of normal. Stronger wave currently located in
central NV is expected to impact the area around this time as
well, setting up the potential for some localized heavy rainfall
to occur. Wouldnt be too terribly surprised Thursday morning to
hear of some localized 1+ amounts of rainfall during the
overnight hours.

Upper ridge then expands back into the mid-section of the country
for the weekend, with 850hpa temps climbing back to around +36C by
00Z Sunday. Fridays highs may need to be trimmed down a skosh
depending on how much rain falls Wednesday night/Thursday morning
and the resultant dwpts. We might need to evaporate some of that
moisture off before the mercury can really climb.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1206 PM MDT Tue Jul 21 2026

VFR conditions will prevail through 22/00z. After 22/00z, some
showers/thunderstorms will move into the region. Localized
MVFR/IFR conds may be possible in heavier rainfall. Have SHRA
mentioned at both TAF sites tonight and overnight, but lower
confidence if the sites will become MVFR/IFR.

&&

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

$$

DISCUSSION...Hintz
AVIATION...Dye