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Area Forecast Discussion (AFD)

Issued by Sioux Falls, SD (FSD)

FXUS63 KFSD 212139

Area Forecast Discussion
National Weather Service Sioux Falls SD
339 PM CST Thu Feb 21 2019

.SHORT TERM...(This evening through Friday)
Issued at 334 PM CST Thu Feb 21 2019

A fairly active short term forecast ahead, as snow returns to the 
region tonight, persists through Friday, and a larger system moves 
across the Midwest on Saturday.  Multiple concerns throughout, from 
sporadic accumulating snows, to persistent freezing drizzle, and 
then potential for near to blizzard conditions on Sunday. 

Tonight: Already starting to see first signs of mid-level warm 
advection over central Nebraska this afternoon, with model
guidance shifting this area northward during the evening. Top-
down saturation continues to be a bit of an issue in model 
guidance, but most solutions begin to saturate a narrow band 
across the cwa during the late evening or early overnight hours. 
Stronger forcing provided by a South to North moving shortwave and
enhanced by broad lift in the right entrance region of an upper 
jet should begin to enhance snowfall over Central Nebraska and 
South Central South Dakota by daybreak Friday. 

Friday: Persistent bands of light to moderate snow will move 
northward through the morning over the western half of the CWA, 
total accumulations by mid-day may range from 3 to 5" in some 
locations. Further east, a lack of moisture should preclude 
anything any widespread precipitation through the day. It's
possible to see light freezing drizzle move into the western CWA
Friday afternoon and early evening behind the departing wave. 

.LONG TERM...(Friday night through Thursday)
Issued at 334 PM CST Thu Feb 21 2019

Friday Evening/Night: Models showing the next shortwave of energy 
with focused low-level warm advection moving in late Friday 
afternoon and through the evening. The focus for snow would take
place along and east of the James River valley. With this wave 
lifting northward late Friday evening, an extended period of 
freezing drizzle may begin to develop across the CWA as ice is
lost in the soundings, but focused especially in the James River 
valley eastward.

Saturday:  Models remain rather consistent in the track of the upper 
low ejecting out of the Texas Panhandle Saturday and secondary 
trough dropping southward out of Canada. As the wave ejects 
northeast Saturday morning, guidance continues to show strong 700 mb 
frontogenesis centered across central Nebraska and into South 
Central South Dakota. The issue with this area of lift is the 
inconsistency in the moisture aloft.  The GFS is a much more 
saturated outlier, producing an intense frontal band eastward and 
merging the band with the incoming upper low.  Other solutions 
support a weakening frontal band, that instead redevelops on the 
northern edge of the upper low across northwest Iowa. Given the 
positioning of the Northern Stream trough, hedged a bit more 
towards the drier solutions of the EC/NAM/CMC.

Saturday Night: A fairly large area of 2-6" of snow may develop over 
the southeastern CWA Saturday afternoon and evening, focused more
heavily in NW and NC Iowa and areas southeast. The next concern 
is the wind. An increasing SPG quickly bumps up sustained wind 
speeds late Saturday night, with gusts approaching 20-25 knots in 
NW Iowa. 

Sunday: The greatest concern on Sunday will be with winds and 
potential for ground blizzard conditions. As the upper wave moves 
into the Great Lakes, most guidance begins channeling 40-45 knots of 
wind at the top of the mixed layer down through the Minnesota River 
valley Sunday morning.  Sustained winds may approach 25 mph with 
gusts to 40-50 possible.  Have blended in CONSMOS guidance and 
pushed gusts to the max value in guidance.  The only real question 
will be how much impact persistent freezing drizzle could have on 
the top layer of snow, otherwise, a winter storm watch for blizzard 
conditions may be considered in later shifts. 

Monday-Thursday: With ongoing busy weather, minimal changes made to 
the forecast.  A minor clipper system will move through Monday and 
again Tuesday bringing light snow accumulations to the area. 
Otherwise the predominate trend will be continued below normal 


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1122 AM CST Thu Feb 21 2019

VFR conditions persist into the evening hours. Warm advection
aloft will bring lower ceilings through the evening, with snow
chances increasing by late evening or early Friday morning. The
greatest impacts will be felt near Huron Friday morning, with
lower and lighter snow amounts in Sioux City and Sioux Falls.
Ceilings could briefly lower to MVFR levels as light snow moves


SD...Winter Weather Advisory from 9 PM this evening to midnight CST 
     Friday night for SDZ038-050-052-053-057>060-063>065-068.