Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 170520
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1020 PM MST Tue Jan 16 2018

.DISCUSSION...(This Evening Through Tuesday)
Issued at 142 PM MST Tue Jan 16 2018

20z surface analysis had low pressure over central AB with warm
front into western NE. Surface low reflection of shortwave trough
energy poking southwest Canada per water vapour with upper ridge
building from the Rockies into the northern Plains. 12z KUNR
sounding showed warm air ready to invade and it is clearly doing
so, most pronounced over the higher elevations. Temperatures
soaring into the 30s and even some 40s over the Black Hills - just
single digits for central SD.

Tonight into Wednesday, shortwave trough zips across south central
Canada taking surface low with it. Warm front will rush through the
CWA with sustained warm air advection leading to widespread readings
crossing the 40F threshold Wednesday afternoon.

Thursday into Friday morning, warm air remains in place with highs
10-20F above normal. Upper ridge shifts east of the CWA as upper
trough deepens across the western CONUS. Some guidance suggesting
potential for stronger downslope winds early Friday given 850mb 50kt
winds and 4mb pressure difference across the Black Hills.

Friday afternoon through Sunday, upper trough with split energy
moves through the northern Plains. Main energy will move well
southeast of the CWA as a couple of weaker northern stream waves
move across the US/Canadian border. Colder air will move into CWA as
surface front sinks through CWA later Friday. Tight baroclinic zone
sets up, but main forcing southeast. Confidence for the location
of the northwest edge of main -SN band is low.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1020 PM MST Tue Jan 16 2018

VFR conditions are expected to continue through the forecast
period.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Sherburn



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