Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 092317
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
417 PM MST Mon Jan 9 2017

.SHORT TERM...(This Evening Through Tuesday Night)
Issued at 204 PM MST Mon Jan 9 2017

20z surface analysis had low over northeast WY with strong arctic
boundary into south central MT and warm front into south central
SD. 40F temperature spreads across the CWA, which will cause havoc
with the forecast for tonight, which focus on baroclinic zone in
place and approaching shortwave over the northern Rockies.

Tonight and Tuesday morning, northern Rockies shortwave will race
across the northern Plains with synoptic lift under 90kt jet streak.
Jet divergence may link up with strong baroclinic zone across the
CWA potentially resulting in a concentrated band of precipitation
late this evening and overnight. Guidance is unclear where this band
will setup, or IF it will set up, but based on latest radar and
satellite trends, it may setup from K2WX to KD07 to KPIR. Have upped
pops in these areas with 1-2 inches possible. Given warm tongue of
air over the dense arctic air, -FZRA possible anywhere tonight where
it precipitates. As forcing shifts east, surface low will move into
eastern NE. This will allow arctic air to surge back south with
subsequent well-defined cold air advection, 25-40kt 850mb winds, and
isallobaric forcing. Looks like BLSN will develop behind front late
this evening in the far north and then into central SD overnight.
Will hoist a winter weather advisory to account for a 6-9 hour
period of BLSN with visibilities less than 1/2 mile at times. Any
fresh snow will exacerbate the BLSN potential. Temperatures will
likely rise this evening and then drop quickly behind the front
tonight.

Tuesday afternoon, gradient relaxes quickly as next low develops
along arctic boundary in western WY ahead of shortwave energy
dropping into the northern Rockies. Winds will quickly subside on
the SD plains, but start to pick up over northeast WY with pressure
falls beginning in earnest over eastern WY/southeast MT.
Temperatures will be chilly in the north and almost normal in the
south.

Tuesday night ahead of arctic boundary, gusty southwest winds are
expected in the west as low moves through WY into western NE. Arctic
boundary will surge back into the CWA with gusty northerly winds
late and much colder temperatures.

.LONG TERM...(Wednesday Through Monday)
Issued at 204 PM MST Mon Jan 9 2017

Upper level flow remains cyclonic over the Northern Plains mid
week as persistent upper low remains over central Canada.
Secondary shot of Arctic air will plunge south early Wednesday,
with some light snow possible across the area. Chances for light
snow will continue into Wednesday night. Any accumulations will be
light. The cooling trend will continue through Thursday as Arctic
air continues to push into the region. Highs will be in the single
digits to teens both Wednesday and Thursday. As skies clear
Thursday night, wind chills will dip into the 20s and 30s below
zero on the SD plains, making it the coldest night this week.

This Arctic shot will be short lived as the main upper trof shifts
east and weak ridging builds in from the west. Temperatures will
modify a bit on Friday, with highs warming into the 20s south and
west - teens across NW SD. As the ridge continues to build, highs in
the 20s and 30s are expected over the weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 414 PM MST Mon Jan 9 2017

Conditions will decrease to MVFR/IFR again this evening with
another round of light snow/rain/patchy -FZRA passing over
northeastern WY, the Black Hills, and northwestern SD mainly between
03Z and 10Z. Gusty southerly winds over northeastern WY will
gradually diminish late this afternoon, and then breezy
northwesterly winds are expected across the area tonight behind a
quick moving cold front. Very gusty winds will be possible after
midnight along the northern and eastern foot hills of the Black
Hills.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from midnight tonight to 11 AM MST
     Tuesday for SDZ013-014-025-026-031-032-072-073.

     Winter Weather Advisory from 9 PM this evening to 11 AM MST
     Tuesday for SDZ001-002-012.

WY...None.
&&

$$

SHORT TERM...Helgeson
LONG TERM...15
AVIATION...10



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