Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 230508
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1108 PM MDT Tue Jun 22 2021

.DISCUSSION...(This Evening Through Tuesday)
Issued at 235 PM MDT Tue Jun 22 2021

Current surface map shows weak trof across eastern Montana into
eastern Wyoming. Northwest flow aloft over the northern plains
this afternoon becomes more westerly Wednesday, with robust low
level warm advection. 900-800mb temperatures support highs near
100F Wednesday afternoon, especially east of the Black Hills.
Weak cold front slips into northeast Wyoming/northwest South
Dakota late Wednesday afternoon. With steep lapse rates and
marginal low level moisture, MLCAPE under 500J/KG for much of the
area. CAMs continue to show a few high based thunderstorms in the
afternoon/early evening. With inverted-v soundings, gusty winds
expected with any thunderstorm.

Better chance of thunderstorms across the area Thursday afternoon
into Friday morning as stronger shortwave slides through the
western Dakotas. Pressure rises of 2-3mb/3hr pressure rises behind
secondary push of cool air will result in a period of gusty
northwest winds early Friday.

For the weekend into early next week, strong upper level ridge
sets up across the Pacific Northwest with trof over the Great
Lakes/Upper Midwest. This will result in warmer/dry conditions for
the forecast area.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1108 PM MDT Tue Jun 22 2021

VFR conditions will continue through the TAF forecast period.
Isolated TS will develop around 21z Wednesday with erratic and
gusty winds into Wednesday evening.

&&

.FIRE WEATHER...
Issued at 235 PM MDT Tue Jun 22 2021

Hot temperatures and very low humidity will be found across the
area Wednesday. Minimum relative humidity will bottom out around
15 percent...with portions of northeast Wyoming dropping to around
10 percent. Winds are expected to remain below Red Flag criteria.
A few thunderstorms are possible Wednesday afternoon.
Gusty/erratic winds will occur near the thunderstorms. With very
little rainfall, there could be some localized pockets of dry
lightning.

There is a better chance of thunderstorms Thursday afternoon into
Friday morning, but we are not expecting any widespread wetting
rains. Dry and warmer conditions will return for the weekend into
early next week.

&&

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

$$

DISCUSSION...7
AVIATION...Helgeson
FIRE WEATHER...7


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