493
FXUS63 KUNR 201714
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1114 AM MDT Thu Jun 20 2024

.KEY MESSAGES...

- Despite cool/cloudy/showery conditions today and Friday, there
will be chances for thunderstorms, mainly across southern parts of
the CWA

- Significant precipitation will be possible over south central SD
through Friday

- Becoming hot and mostly dry this weekend into next week

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 206 AM MDT Thu Jun 20 2024

The northern plains is beneath southwest flow, between
an upper trough to the west and a ridge to the east. High pressure
across the southeast is advecting plentiful moisture in from the
Gulf of Mexico. Combined with some weak shortwave energy,  this
moisture advection is resulting in some showers and weak
thunderstorms across central SD early this morning. A surface high
sits to our northeast, and a surface low to our southwest, producing
southeasterly winds of 10-20 kts across the CWA. Temps are falling
into the 50s.

Low and mid-level moisture will continue advecting into the region
today. Upslope southeasterly winds will aid in the development  of
low clouds, drizzle, and patchy fog today, especially across the SD
plains. Highs will be only in the 60s where the low clouds persist;
however, far southern SD and especially northeastern WY will warm
into the 70s. MUCAPE will increase across southern SD to 1500-2000
J/kg, with CIN weakening, as a series of weak shortwaves approaches
this afternoon and evening. With 0-6 km shear around 40 kts, strong
to severe storms will be possible. Another threat will be heavy rain
across south central SD, the same area receiving rain this morning.
PWATs are still predicted to be 150-200% of normal, and 1-2 inches
of precipitation will be possible there with this evening`s storms
alone. The 6-hr FFG is 2.5-3.5 inches, so not expecting any flooding
issues, but it is worth watching. Tonight, expecting fog to expand
across much of the CWA.

Cool, moist airmass lingers over the region Friday, and temperatures
will be only slightly warmer than today`s. Buoyancy will increase
across the warmer areas of northeastern WY and southern SD again,
and as a more potent wave approaches Friday afternoon, storms may
initiate across northeastern WY. Shear will be sufficient for
supercells; however, uncertain how far these storms will be able to
progress across much of our CWA with a staunch cap in place -
perhaps again they will stay mainly across southern SD. PWATs will
be high again, and so heavy rain is expected...potentially over
south central SD again. By 12Z Saturday, ensembles` total QPF 50th
percentile have 2-2.5" for south central SD. Still thinking the
soil/sand will be able to hold this moisture; however, if more
precipitation than expected falls tonight, additional precipitation
Friday night will be of more concern.

The weather will begin to feel more like summer 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 18Z TAFS Through 18Z Friday)
Issued At 1113 AM MDT Thu Jun 20 2024

Widespread MVFR/local IFR ceilings across much of western South
Dakota into portions of NE Wyoming will continue through this
afternoon and evening. Local MVFR/IFR visibility in fog will
persist around the Black Hills. Scattered showers and
thunderstorms are expected today and tonight with local IFR
visibility near any storms. Low ceilings will persist through the
overnight hours, with some gradual improvement after 14-16z
Friday.

&&

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

$$

DISCUSSION/KEY MESSAGES...Pojorlie
AVIATION...SE