Area Forecast Discussion
Issued by NWS Rapid City, SD

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196
FXUS63 KUNR 171919
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
119 PM MDT Mon May 17 2021

.DISCUSSION...(This Evening Through Monday)
Issued at 101 PM MDT Mon May 17 2021

Water vapor shows cut off low over the Four Corners with weak
ridge over the northern tier of states. Next upper low is offshore
the Pac NW coast. At the surface, return flow is strengthening
with pres falls along the front range. A few weak -shra are noted
over south central SD.

Other than a few evening -shra over southern SD, fairly benign wx
expected today. Could be a touch of fog again tonight, but
strengthening low level flow should limit coverage.

Southwest flow aloft will develop Tuesday and will continue
through the weekend as upper low currently offshore the Pac NW
slowly digs southeast through the western CONUS. The result will
be near to above average temps most days this week (but a little
cooler over the weekend), and daily chances for precip.
Instability will increase slightly Tuesday south/east of the Black
Hills for a few afternoon/evening storms. A better chance of
storms arrives Wednesday as a northern stream short wave crosses
southern Canada and picks up the Four Corners low, while also
sending a weak cool front through the Northern Plains.

A slower moving cold front will cross on Thursday and Friday,
providing the best chance for some stronger to a few severe storms
as ejecting upper waves pass overhead. Coverage of storms on
Thursday is somewhat in question depending on strength of dry
slot.

Continued unsettled and a little cooler wx expected over the
weekend with upper low over the western CONUS moving very little.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Tuesday Morning)
Issued At 531 AM MDT Mon May 17 2021

MVFR/IFR conditions, along with areas of fog and LIFR conditions,
will persist across the southwest and south central SD plains
early to mid morning. Patchy fog is expected across the Black
Hills and northwest SD early today. Conditions will improve by
late morning. Breezy southeasterly winds will develop across much
of the plains later this morning and afternoon. Patchy low clouds
and fog could redevelop later tonight/early Tuesday across many of
the same areas as this morning.

&&

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

$$

DISCUSSION...Johnson
AVIATION...26



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