Rapid Valley, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

669
FXUS63 KUNR 190429
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1029 PM MDT Thu Jun 18 2026

.KEY MESSAGES...

- Increasingly unsettled this weekend with beneficial rainfall for
  many and the possibility of isolated severe thunderstorms later
  Saturday.
- Elevated fire weather conditions Friday
- Cooler temperatures for Sunday through Tuesday, then a gradual
  warm up for the rest of next week.

&&

.UPDATE...
Issued at 1027 PM MDT Thu Jun 18 2026

03z surface analysis had weak trough bisecting the CWA in response
to compact shortwave energy over central ND. This wave assisted a
cluster of thunderstorms under 110kt jet. 00z KUNR sounding was
mixed to 540mb with an inverted-V thermo profile which supported a
series of convective wind reports across northwestern SD this
evening along with a couple of severe thunderstorm warnings.
Latest guidance suggests jet will support a few showers overnight
from southeast MT into north-central SD with PoPs adjusted. Current
forecast in pretty good shape after tonight.

Mostly dry Friday will give way to increasingly unsettled weather
for the weekend. Northwest flow aloft will become west as a
series of disturbances move through the CWA inducing southeasterly
low-level flow and a good fetch of low-level moisture (PWATs
rising to 100-150% of normal). Buoyancy Saturday
afternoon/evening will be modulated by early Saturday cluster of
shra/TS. If atmosphere recovers enough over northeastern
WY/southwestern SD, active/severe storms may develop given
forecast shear, especially northeast of surface low which will be
located over central WY. Chance of QPF by 12z Monday >1.00" is
>50% from the Black Hills eastward. Beneficial if it fully
materializes for sure.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 155 PM MDT Thu Jun 18 2026

Latest satellite imagery shows continued northwest flow over the
CWA. A few showers are starting to dot the landscape but rain
amounts will be negligible.

Looking ahead to tonight and tomorrow, we`ll continue the chances
for isolated showers and non-severe storms trying to drift in
from the north and northwest. Temperatures will be near-normal
with overnight lows in the 40s to low 50s and afternoon highs in
the 70s to low 80s.

Friday night and the weekend will see a weather pattern change
that will bring very different weather. The upper level
northwesterly flow will shift to a more westerly flow as a high
pressure builds over the desert southwest. At the surface, a lee
side low looks to develop in eastern Colorado. This pattern will
bring rain, and thunderstorms to the central plains, including
western South Dakota and northeast Wyoming.

With forecasted PWATs nearing 150% of normal in some models,
there is potential for heavy rain. The WPC has put most of western
South Dakota and northeast Wyoming in a marginal risk for
excessive rainfall. Saturday morning to Monday morning rainfall
amounts could be quite impressive; the EURO and GFS ensemble`s
75th percentile for Saturday and Sunday rainfall amounts are
around 1 to 1.5 inches, heaviest rain in south-central South
Dakota. The 25th percentile is around 0.50 to 0.75 inches. So
based on that, there is a solid chance for widespread 48 hour
rainfall amounts near 1 inch in western South Dakota.

The SPC has a slight risk of severe weather centered over the
KS/NE border but the surrounding Marginal Risk does spread into
southwestern SD. At this time, main concerns would be gusty winds
and hail.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 948 PM MDT Thu Jun 18 2026

VFR conditions are expected through the forecast period.
Isolated/scattered shra/TS will continue into the overnight hours
across (mainly) northwestern SD and extreme northeastern WY.

&&

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

$$

UPDATE...Helgeson
DISCUSSION...GS
AVIATION...Dye