Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 202337

Area Forecast Discussion
National Weather Service Sioux Falls SD
537 PM CST Tue Feb 20 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 256 PM CST Tue Feb 20 2018

It`s a chilly late February day across the region, as low level cold
air advection continues under a sunny sky. A few lingering
flurries continue this afternoon across the Tri-State area, but
should dissipate quickly by sunset. The primary concerns in the 7
day forecast remain focused on cold temperatures tonight, along
with a prolonged light snow event Thursday and Friday.

Tonight:  High pressure is expected to slowly settle southeast after
midnight, which will result in winds eventually turning light and
variable by daybreak Wednesday.  Models are a bit split with their
wind solutions, some a bit stronger, others nearly calm, which has a
bit of an impact on the overnight lows.  Given the clear skies and
fresh snow and light winds, will trend towards the colder solutions
suggesting overnight lows in the double digits below zero in the
more sheltered locations.  I am a bit concerned with the slight warm
air advection at the 950:925 mb layer along with the 15 knots of
flow keeping temperatures in the MO river valley slightly warmer.
Nevertheless, even with a light wind, overnight wind chills drop
between -20 and -25 west of the James River, so will go ahead and
issue a wind chill advisory.

Wednesday: High pressure drifts to the southeast and east by the
afternoon which should induce a southerly surface flow.  Most areas
however will remain stuck in the teens, but 20 degree readings will
sneak into the southern and southwestern CWA

.LONG TERM...(Wednesday night through Tuesday)
Issued at 256 PM CST Tue Feb 20 2018

Thursday-Friday: This is the primary focal point for wintry
weather in the forecast. Deep southwesterly flow aloft will send a
series of minor shortwaves northeastward. Models are in
reasonable agreement with these system. 00Z and 12Z ECMWF are both
focused a little further to the NW and remain slightly higher
with QPF values than the other higher resolution models. That
said, expectations are that broad warm air advection coupled with
weak upper divergence will allow light snows to develop by mid-day
Thursday. Rates won`t be intense, but a prolonged period of light
snows will be expected into Thursday night. Soundings suggest
that we`ll lose some saturation by Thursday night, as a secondary
PV anomaly also lifts north. There could be intermittent freezing
drizzle or light snow continuing into Friday morning. Have bumped
up PoPs from the populated blends given confidence in the
forecast solutions.

Once the precipitation moves northeast, the daytime hours Friday
will remain cold, but should remain dry. With high pressure moving
through, winds should be weak enough to avoid any blowing snow.

Generally QPF and snow accumulations will be on the lighter side
again for this event. Fairly widespread snow amounts between 1-3
inches are likely with a minor glaze of ice into Friday morning.

Saturday-Sunday: Eventually a more progressive trough moving into
the Pacific Northwest will sweep southeast by Saturday, forcing
energy lingering over the Central Rockies eastward. This wave
should track across Kansas and Missouri on Saturday and only graze
the southern half of the CWA as it moves through. GFS/ECMWF are
in decent agreement giving the potential for a light accumulation
of snow into Saturday night.

Cold advection returns for Sunday, and will again keep temperatures
below normal in most locations. A subtle wave dropping south of out
Canada could bring light flurries in the 2nd half of the day and
into Sunday night.

Monday-Tuesday: A return to westerly and southwesterly flow aloft
next week should allow temperatures to warm back to near and above
seasonal normals.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 529 PM CST Tue Feb 20 2018

Occasional MVFR ceiling will continue across portions of northwest
Iowa through around 02Z Wednesday. Otherwise, VFR conditions
through the TAF period.


SD...Wind Chill Advisory from 11 PM this evening to 10 AM CST
     Wednesday for SDZ038>040-050-052>061-063>065.

MN...Wind Chill Advisory from 11 PM this evening to 10 AM CST
     Wednesday for MNZ071.



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