Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201652
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1052 AM MDT Mon Mar 20 2017

.SHORT TERM...(Today Through Tuesday Night)
Issued at 236 AM MDT Mon Mar 20 2017

Unsettled weather can be expected in the period as active
westerly flow will interact with a batch of cp air advecting into
the region. Impulse traversing the northern plains this morning
has supported a few high based shra across the NW fa. Initial cold
front has settled south over the fa with cooler conds the result
today as most places will see 50s for highs. Another upper trough
will affect the region tonight, with rain and snow likely over
most of the area. Deep upper trough advancing across southern
Canada will eventually force cp back into the fa tonight as the
next system arrives. Hence rain will transition to snow. HIRES
models continue to indicate the potential for more concentrated
fgen banding Invof the SD/NE border where a band of heavier
precip could be found later tonight. Expecting a quicker
transition to snow than what current guidance suggest. However,
warm ground and initial warm thermal fields will fight accums.
Expecting an inch or less most areas that see snow with around 2
possible where more persistent snows develop, possibly higher if
precip quickly transitions to snow in the aforementioned fgen
band. Snow will linger and wane Tue morning with cool moist
upslope flow expected through Tue. Added a fog mention over the
Black Hills and eastern foothills with persistent easterly flow
tonight through Tue night. Moist upslope flow will highly limit T
rises, esp over western SD Tue. The next system will arrive Tue
night and support staunch WAA with a band of fgen precip expected.
Given ll thermal structure with warm nosing aloft, a wintry mix
will be possible and have added a mention of freezing rain, mainly
on the SD plains with some light icing possible.

.LONG TERM...(Wednesday Through Sunday)
Issued at 236 AM MDT Mon Mar 20 2017

Active progressive flow on track the remainder of the week,
supporting unsettled conds. Long wave trough will affect the
region Thur-Fri with another system next Sunday. Still many
details to be worked out with these systems, namely track, trough
fracturing, and CAA/thermal fields. Models have recently zoned in
on a more consistent solution wrt the Thur-Fri system taking the
main upper trough and sfc low well south of the region. However,
the lead LSA with the advancing upper trough could still give the
SE zones a decent amount of precip if enough ll moisture can
advect north. Near seasonal to slightly above seasonal temps
expected in the period, with breezy conds.track of storm.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1047 AM MDT Mon Mar 20 2017

Spotty -SHRA/virga will persist this afternoon across northwest
SD with local MVFR conditions. Spotty -SHRA/virga will develop
over northeast WY and the Black Hills later this afternoon.

An organized disturbance will bring widespread -RASN to the area
tonight, starting over WY and then spreading into western SD.
Conditions will deteriorate with widespread IFR CIGS/VSBYS due to
stratus/precipitation. Local LIFR conditions expected with the
heaviest snow bands and near the Black Hills where fog will
develop overnight and continue Tuesday.

&&

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

$$

SHORT TERM...JC
LONG TERM...JC
AVIATION...Helgeson



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