Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 191124
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
524 AM MDT Sat May 19 2018

.DISCUSSION...(Today Through Friday)
Issued at 205 AM MDT Sat May 19 2018

08z surface analysis had wiggly frontal boundary from northern UT
into the central Plains into the upper Midwest. High pressure
over south central Canada nosing into the northern Plains with low
level upslope northeast boundary layer flow over the CWA. This
flow assisting some DZ/FG that has developed recently, noted on
KUDX radar. Upstairs, water vapour had upper low over northeast
CO. Convection associated with upper low decreasing as instability
wanes. Short term concern is the upper low.

Today, upper low meanders into central NE as it weakens and upper
ridge moves into the northern Rockies. Surface high continues to
build in with drier air increasingly pulled into the CWA. Result
will be decreasing chances for precipitation as well as fog. Have
trimmed pops significantly this afternoon, except near the NE
border. Temperatures will be warmest across the north where best
sunshine occurs.

Tonight, any leftover precipitation ends early as surface high
becomes dominate. Temperatures will be near guidance.

Sunday, surface high shifts east with return flow and warm air
advection. Southwest flow aloft develops as another upper
trough/low deepens across the far western CONUS. Temperatures
will be near guidance.

Monday through Wednesday, upper trough spins a series of shortwaves
into the CWA under southwest flow aloft. TSRA chances warranted
given low level moisture return. Temperatures will be 5-10F above
normal.

Thursday into Friday, uncertainty increases as upper low ejects
into south central Canada and then moves away as upper ridge
builds over the Rockies. PoPs continue with slightly above normal
temperatures.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 520 AM MDT Sat May 19 2018

Widespread MVFR-IFR and local LIFR conditions with drizzle and fog
can be expected across the SW 2/3 of the forecast area this
morning, with rain slowly trending south during the day. Drier
air will move into the area from the north today with flight
conditions improving north to south by late this afternoon.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...15



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