Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 172147

Area Forecast Discussion
National Weather Service Sioux Falls SD
347 PM CST Sat Feb 17 2018

.SHORT TERM...(This evening through Sunday)
Issued at 342 PM CST Sat Feb 17 2018

Skies will remain mostly clear through this afternoon and evening,
with high temperatures into the 30s for most. During the early
overnight, a strong jet streak develops over North Dakota associated
with a robust upper-level shortwave. This will provide the forcing
for a strong surface low which will slide eastward though South
Dakota Sunday morning. Winds will be breezy as the pressure gradient
tightens with south winds in the 30+ mph range are likely during the
morning hours. It continues to look like precipitation associated
with this system will stay along and north of the Dakotas` mutual
border. Mid-level clouds will be widespread, but no snow is expected
until later Sunday evening.

.LONG TERM...(Sunday night through Saturday)
Issued at 342 PM CST Sat Feb 17 2018

On Sunday evening, winter weather return to our area. The set-up for
this event is less straight forward than usual, as multiple
shortwave troughs will be moving northeast through the downstream
side of a longwave trough centered over the Western CONUS. Sensible
weather-wise, this will lead to an extended period with snow,
freezing drizzle, and sleet impacting travel.

Snow will start in south central South Dakota and quickly spread
north and east Sunday evening, affecting locations such as
Chamberlain, Brookings, and Marshall. After midnight, a sleet and
freezing drizzle mix develops over northwest Iowa, as arctic air
surging southward interacts will warm, moist northerly flow into a
warm front that stretches eastward along the Iowa-Minnesota border.
There is increasing confidence in this scenario, with the most
recent runs showing a deeper and colder surface layer, which could
make sleet and ice pellets more common. Accumulating sleet and at
least of light coating of ice looks increasingly likely for places
such as Storm Lake and Spencer, IA, perhaps reaching as far west as
Sioux City and as far north as I-90 in southwest Minnesota. This
wintry mix looks to last until Monday afternoon. Meanwhile, for
southeast South Dakota and areas northwest of Hwy 60 in southwest
Minnesota, light snow will slowly be accumulating throughout the
day. Accumulations will be higher the farther west one moves, with
places like Huron and Chamberlain, SD seeing the best chances for
several inches of snow.

Monday night, another round of snow looks to add a couple more
inches to the totals from Monday, as another shortwave trough moves
through the upper-level flow. This band of snow sweeps eastward
through the region into Tuesday morning, after which time colder,
drier air and decreasing dynamics ends snowfall.

Tuesday and Wednesday temperatures will be cold as an arctic surface
high builds into the region, with morning wind chills in the -20s.
On Thursday temperatures will moderate, with highs reaching around
freezing, which is close to normal this time of the year. Another
winter system is possible on Friday, but given model disagreement,
confidence is very low.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1142 AM CST Sat Feb 17 2018

A round of snow showers will move east early this afternoon,
bringing an hour of light snow and reduced visibilities. Behind
these showers, lingering mid-level cloud cover will last into the
evening. The early overnight looks clear, before clouds move in
from the west. After midnight, 18/0600z, strong south winds a
couple thousand feet AGL will cause up to 40 to 60 kts of low-
level wind shear, depending on location. These values are
noteworthy, and are due to the strong low pressure system passing
to the north of the region.




SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...VandenBoogart is the U.S. government's official web portal to all federal, state and local government web resources and services.