Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 100428

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
928 PM MST Fri Dec 9 2016

Issued at 848 PM MST Fri Dec 9 2016

Cold high pressure remains over central SD with temperatures from
-10 to 10. Frontal boundary across northwestern-southeastern WY
and southern NE panhandle. Strong inversion about 2K feet above
the ground on UNR sounding with temperatures rising about 14
degrees is helping to keep low clouds in place. RIW sounding is about
20 degrees warmer above the inversion than UNR. Temperatures have
started to warm across central WY with warm air advection
spreading across northeastern WY and the Black Hills overnight
ahead of storm system eastern ID-southwestern MT. Increasing
isentropic lift above the front will produce light snow over
southwestern SD and the Black Hills area this evening...then
spread eastward overnight. Accumulations will be light.


.SHORT TERM...Saturday and Saturday Night
Issued at 230 PM MST Fri Dec 9 2016

Highs Saturday will vary greatly depending on the side of the
front...with northwest SD in the single digits while northeast WY
and southwest SD reaches the low 30s. The biggest gradient could
be along the northern foothills as the Black Hills warm into the
low 30s and the surrounding plains reach the upper teens to low
20s...or potentially colder if the arctic airmass has a tough time
getting flushed out.

This band of snow will then move into central SD by Sat morning.
Accumulations will be light...under an inch. Most areas will see
drier weather during the day tomorrow on the backside of the
departing snow. Upper flow will become zonal with a strong
shortwave crossing the Cascades and northern Rockies. 800mb low
will cross the CWA Sat evening with chances for snow increasing
again through the night. Colder air will push back into the area
on the backside of the low as it pushes E/SE of the CWA.

.LONG TERM...(Sunday Through Friday)
Issued at 230 PM MST Fri Dec 9 2016

Fast moving shortwave exits the area early Sunday. May be some
lingering light snow across southwest South Dakota, otherwise some
sunshine and slightly warmer temperatures expected. Sunday will be
the warmest day of the extended, even though temperatures will be
10-15F below average. Reinforcing shot of arctic air arrives
Monday, with falling afternoon temperatures. Dry weather expected
for the middle of the week with highs 20-25F below average.
ECMWF/GEFS still pointing to widespread snow next weekend, along
with the very cold temperatures.


.AVIATION...For the 00Z TAFS Through 00Z Saturday Evening
Issued At 418 PM MST Fri Dec 9 2016

Areas of MVFR/LCL IFR conditions in light snow and stratus will
cont acrs swrn and scntrl SD this even. Snow over swrn SD will
spread eastward overnight, with widespread IFR conditions thru
Sat mrng. Snow wl dcrs Sat aftn, but MVFR cigs wl linger acrs wrn
SD plains.




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