Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 122050
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
250 PM MDT Wed Aug 12 2020

.DISCUSSION...(This Evening Through Wednesday)
Issued at 250 PM MDT Wed Aug 12 2020

W/SW upper flow has developed across the CWA, ahead of a trough
crossing the Pac NW. Surface trough/dryline has pushed through the
Black Hills area into the adjacent plains to the east, as far as
Wasta. RH has dropped off to 15 percent or less behind the dryline.
KUDX radar shows isolated showers/storms developing across portions
of northeast WY through SW SD. CAMs continue to show more
development over the next few hours, but hail is unlikely given the
very weak CAPE. Gusty winds are much more of a possibility, with the
inverted V boundary layer. Once the storms dissipate this evening,
dry weather is expected through morning hours. More storms are
expected Wednesday afternoon across the Black Hills and into
northwest SD toward Thursday night as a cold front pushes through.
The best chances for storms will be across NW SD as a strong wave
pushes across ND in the overnight hours. Temps will be cooler for
Friday and through the weekend, with highs in the 80s. Strong upper
ridging across the western CONUS will keep ridge riding waves across
the region and daily chances of isolated storms. But overall, a dry
pattern is expected into early next week, with near average
temperatures.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1203 PM MDT Wed Aug 12 2020

Isolated thunderstorms are possible across western South Dakota
this afternoon and evening. Local IFR conditions are possible with
the thunderstorms. Otherwise, VFR conditions are expected through
the forecast period.

&&

.FIRE WEATHER...
Issued at 250 PM MDT Wed Aug 12 2020

Hot, dry, and breezy conditions continue across northeast WY into
far western SD. Many locations have reached red flag warning
criteria, though not necessarily in duration, across northeast WY
through the Black Hills, even out to the Wasta DOT site. Many more
locations are flirting with reaching criteria. Have expanded the
Red Flag Warning to cover the Black Hills and adjacent plains.
Some storms have developed in the last hour across northeast WY
and southwest SD, so dry lighting is definitely a concern. Have
also extended the warning through the overnight hours, given the
poor humidity recovery. Most areas within the warning area will
not reach above 50% RH overnight. Similar conditions are expected
again Thursday afternoon, with RHs dropping down to 10% and wind
gusts getting close to...or surpassing...criteria values. Red
Flag Warning is out until 8 PM MDT tomorrow.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 8 PM MDT Thursday for SDZ319>327-329-332.

WY...Red Flag Warning until 8 PM MDT Thursday for WYZ314>318.

&&

$$

DISCUSSION...13
AVIATION...13
FIRE WEATHER...13


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