Area Forecast Discussion
Issued by NWS Rapid City, SD

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984
FXUS63 KUNR 172016
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
216 PM MDT Wed Jul 17 2024

.KEY MESSAGES...

- Near average temperatures with a daily chance of thunderstorms
  through the weekend. Isolated severe storms possible.

- Trending warmer and drier for the first half of next week.

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 140 PM MDT Wed Jul 17 2024

Current analysis shows northwesterly flow aloft, resulting from
an upper ridge building to the west of the forecast area and a
trough sweeping across the Great Lakes Region. At the surface,
high pressure over the ern Dakotas/wrn MN is producing light
northeasterly surface winds over the forecast area.

Dewpoints in western SD are in the mid-50s to around 60F and in
the 40s over northeastern Wyoming. MLCAPE has risen to around
500J/kg over much of the area, with a max of >1500J/kg over
southwestern SD and near the eastern slopes of the Black Hills.
Due to the instability, scattered thunderstorms have already
initiated along the convergence zone over the central and southern
Black Hills, with large hail reported earlier this afternoon near
Hot Springs. Damaging wind gusts will also be possible today.
Storm motion for the stronger storms coming off the hills has been
nearly straight south, with the weaker storms moving a bit more
to the southeast. Storms have also developed over the higher
terrain to the west and southwest of the forecast area. Storms
developing in the vicinity of the Bighorns may track into Campbell
county Wyoming and then eastward into Weston county as the
afternoon progresses, and then possibly continuing eastward into
southwestern SD this evening.

The setup looks to be much the same for Thursday, with the best
chances for strong to severe storms again over and near the Black
Hills, extending southward into southwestern SD.

A stronger shortwave will round the upper ridge Thursday night,
dropping across the western Dakotas on Friday. This will bring
scattered thunderstorms to much of the area Friday afternoon/evening
with again a wind/hail threat.

The ridge will becomes a bit more amplified over the weekend with
northerly flow aloft over the Plains. Embedded impulses will keep
chances for thunderstorms in forecast each day. Early next week,
eastern the Pacific trough will nudge the ridge to the east,
resulting in warmer/drier conditions across the forecast area.


Current surface map places high pressure across the Dakotas with a
few mid clouds across the area. Persistent upper level ridge
remains across the Intermountain West with northwest flow across
the plains. Surface high slowly slides southeast today into
Thursday with an uptick in return flow across northeastern Wyoming
and far western South Dakota. Residual low level moisture and
steep mid level lapse rates maintain some buoyancy across the
area. Most of the area will remain dry today and Thursday, with
any thunderstorm activity limited to northeastern Wyoming and the
Black Hills/southwestern South Dakota. Higher DCAPE across
northeastern Wyoming will favor strong wind gusts with any robust
thunderstorms, while deeper moisture and shear will result in a
hail/wind threat to the Black Hills region.
&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1115 AM MDT Wed Jul 17 2024

VFR conditions are expected through the forecast period. An
isolated shower/storm is be possible this afternoon, mainly over
the central Black Hills into southwestern SD. Transient MVFR
conditions can be expected in/near any storms in addition to
gusty, erratic winds.

&&

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

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...SE