358
FXUS63 KUNR 210739
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
139 AM MDT Fri Jun 21 2024

.KEY MESSAGES...

- Another cool/cloudy/showery day, with another chance for
thunderstorms this evening, especially across northeastern WY

- The risk of flooding continues across south central SD, with more
rain on the way

- Becoming hot and mostly dry this weekend into next week

&&

.DISCUSSION...(Today Through Thursday)
Issued at 137 AM MDT Fri Jun 21 2024

High pressure across the southeastern CONUS and a
trough over the west coast continue to help moisture advect into the
northern plains. Shortwave energy moving through southwest flow are
contributing to thunderstorms across NE/SD. Between a surface high
to our northeast and a surface low to our southwest, winds are light
and northeasterly across the CWA, resulting in areas of fog across
the western SD plains. Temperatures are in the 50s to lower 60s.

Another cool, cloudy, showery day is expected, with highs only in
the 60s and lower 70s. Another round of showers is expected to move
through south central SD this morning, bringing additional
precipitation to already saturated ground. Fog, or at least low
stratus, will persist into the afternoon across most of the western
SD plains. Northeastern WY will have a better chance at some sun,
and with the plentiful moisture around, MUCAPE  of 1000-1500 J/kg
could develop. As a more potent shortwave approaches the region late
this afternoon, thunderstorms are expected to develop across eastern
WY and push into SD. Strong to severe storms will be possible across
northeastern WY, but the strong cap will limit severity over much of
the cloudy SD plains.

Nonetheless, another round of rain will move across the CWA tonight.
PWATs remain 150-200% of normal, and so heavy rain will again be
possible. If additional precipitation falls over south central SD,
ongoing flooding will be exacerbated. Obs show 2.5 to 3.5 inches of
rain have already fallen (with locally higher amounts) across parts
of south central SD. HREF has only a 30-40% chance of >1" of precip
falling over south central over the next 24 hours. The latest 6-hr
FFG has about 0.2" to 2" across Tripp County, and so will keep the
Flood Watch going there. Considered expanding to Todd and Mellette,
but FFG is a bit higher there; additionally, most of the QPF in our
forecast is for 00-06Z, a period when CAMs are about 50/50 on
whether there will be storms across south central SD at all.
Considering the uncertainty, will leave Todd and Mellette out of the
Flood Watch.

More summery weather is expected this weekend, as a ridge begins
to build over the Rockies. Highs will warm back into the 80s
Saturday, near 90 Sunday, and well into the 90s Monday. Hot
weather will continue through the week, and conditions will be
mostly dry, although cannot rule out an isolated thunderstorm each
day.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 935 PM MDT Thu Jun 20 2024

Widespread IFR conditions (low ceilings/lower VSBYS due to
fog/drizzle) are expected over western SD into far northeastern
WY overnight. MVFR/local IFR conditions will push into parts of
northeastern WY (including KGCC terminal) late tonight into Friday
morning. VSBYS should improve Friday morning, but ceiling
improvement will slow. Scattered/numerous showers/thunderstorms
will move through at times.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Flood Watch through Saturday morning for SDZ049.
WY...None.
&&

$$

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