Area Forecast Discussion
Issued by NWS Rapid City, SD

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789
FXUS63 KUNR 241715
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1115 AM MDT Wed May 24 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 208 AM MDT Wed May 24 2017

Potent NW CONUS upper trough will force a low pressure system and
associated low pressure trough into the region today/tonight.
Large scale pattern will then become blocked once again with the
aforementioned upper low stalling over the northern CONUS for
several days. Shortwave ridging ahead of the upper trough will
support a warm more seasonable day across the region with highs in
the 70s/80s, the warmest day in the next 7 days. SE return flow
will increase with gusty SE winds developing on the plains, esp NW
SD. Broad LSA coupled with diurnal instability and the
approaching trough may fire a few isold shra/ts this afternoon
across the far NW, esp NE WY. However, better chances for sct shra
will be this evening as the main lobe of ascent shifts east
across the region. Best chances for shra will be across far NW SD,
with more isold activity possible ahead of the sfc trough further
south. Dry conds can be expected Thur as large scale subsidence
spreads over the region with very dry BL conds. Strong ll flow
coupled with deep mixing and CAA will support windy conds on the
NW SD plains Thur, with adv conds expected at many locations
there.

Closed low will slowly shift east with several weak impulses
rotating around the low, advecting through the region. This will
support cool and unsettled conds through the weekend, with near
daily chances for shra. Southern stream impulse will phase with
the northern CONUS trough Sat, resulting in a decent FGEN response
coupled with pos theta-e adv. Forecast models are favoring the
SD/NE border area attm for a decent rain event. However, further
track adjustment is likely per this feature. Upper low will
finally shift east by Mon-Tue of next week as the western CONUS
ridge trends east. This will support a warming and drying trend by
mid next week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1113 AM MDT Wed May 24 2017

VFR conditions and gusty southerly winds can be expected today.
Isolated to scattered storms will develop late this afternoon into
the evening ahead of a cold front. MVFR conditions are possible
near heavier storms. Behind the front...gusty winds will switch to
the northwest mid to late evening.

&&

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

$$

DISCUSSION...JC
AVIATION...13



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