Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222334

Area Forecast Discussion
National Weather Service Sioux Falls SD
534 PM CST Fri Feb 22 2019

.SHORT TERM...(This evening through Sunday)
Issued at 304 PM CST Fri Feb 22 2019

Active weather pattern just keeps going and going.

For the rest of today, light snowfall will continue to focus across
the western half of the forecast area, especially west of the James
River in the vicinity of the 700 mb frontogenesis. By early evening
however, the the active southwest flow aloft directs the next subtle
shortwave into the Missouri Valley then southwest Minnesota
overnight. The light snowfall will begin to advance eastward this
evening, however drier air in the low/mid levels clouds across the
eastern half of the forecast area could slow in initial progress
of the snowfall. Loss of saturation in the dendritic zone this
evening with persistent dry air in the mid levels will likely
allow precipitation to mix with light freezing drizzle at times.
The drier air aloft should limit any additional snowfall amounts,
especially late this evening and overnight. Models do suggest that
some frontogenesis develops across our far southeast late
afternoon and evening, which could potentially bring some greater
snowfall amounts. Think that this area could see 1 to 3 inches of
snow, while elsewhere less than an inch is expected.

Even with a greater threat for freezing drizzle, icing accumulations
will also be relatively light, with only a light glaze of ice
expected. While the initial wave exits the area late tonight, lower
clouds and broad lift will keep patchy freezing drizzle in the
region into Saturday morning.

Models are in pretty good agreement with the timing and track of the
next storm system. The main shortwave trough arrives in the central
Plains on Saturday, becoming a closed circulation over Kansas as it
lifts northeast through the afternoon. Light snow will start
spreading across the Missouri Valley around late morning into
midday, spreading north and east in the afternoon. The best
potential for and inch or more of snowfall remains across the
southeastern half of the forecast area, largely southeast of a
Yankton to Marshall line. Strong forcing and lift sets up near the
southeastern corner of the forecast area (just south of Storm Lake
and Ida Grove) in the afternoon, and will allow for heavy snowfall
rates to develop in our extreme southeastern counties. There remains
some uncertainty in how far north the heaviest precipitation falls,
so have decided to go with a winter weather advisory for northeast
Nebraska and much of northwest Iowa for Wednesday afternoon and
evening, roughly following where 3 inches or more of snow is
expected. On the higher end in BV and Ida counties, amounts could
approach 6 inches, but with uncertainty in how far north the heavier
QPF pushes, will leave in an advisory for now. In addition to the
snowfall, winds will be on the increase, creating further reductions
in visibilities. The strongest winds, however, hold off until the
end of the falling snow.

The surface low becomes very tightly wrapped as it tracks through
northern Missouri and central Iowa. Winds will increase through the
day on Saturday, with gusts increasing to 30 mph. Northerly winds
increase further in the evening, with gusts reaching as high as 40
to 50 mph by midnight across much of southwest Minnesota and
northwest Iowa. Although the snowfall will have ended, expect ground
blizzard conditions of near white-out conditions from blowing snow
where the winds are strongest. Will upgrade the weather storm watch
to a blizzard warning, largely for ground blizzard conditions from
midnight early Sunday through Sunday afternoon. May need to look
into the potential for a winter weather advisory for blowing snow
further west, but will leave it to just the warning with this event
over 24 hours out yet. Am also concerned how much the freezing
drizzle could create a crust on the existing snowpack to the west
of the warning, therefore limiting the blowing snow potential.

Windy conditions continue into Sunday, with the strongest winds
remaining across our eastern half.

.LONG TERM...(Sunday night through Friday)
Issued at 304 PM CST Fri Feb 22 2019

With the focus on the winter weather tonight into Sunday, did not
make much adjustment to the extended grids. It does look like a
thermal boundary sets up across the northern Plains for the first
half of the week, bringing precipitation chances around the Sunday
night time frame and again Monday night. The screaming message
remains: very active and wet pattern continues.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 531 PM CST Fri Feb 22 2019

Light snow struggling this evening as dry air continues to prevent
top-down saturation. With moisture trying to increase from the
south, anticipating a period at all the terminals with light snow
this evening, before mid-level forcing moves off and moisture is
again lost overnight.

At that point, light freezing drizzle may be possible into
Saturday morning.

Upper low expected to move through Nebraska and into Iowa Saturday
afternoon with moderate snow impacting Sioux City by mid-
afternoon. Sioux Falls may reside just on the edge of this snow
area, so left a more optimistic outlook in TAF.


SD...Winter Weather Advisory until midnight CST tonight for SDZ038-

MN...Blizzard Warning from midnight Saturday night to 6 PM CST Sunday
     for MNZ071-072-080-081-089-090-097.

IA...Winter Weather Advisory from noon Saturday to midnight CST
     Saturday night for IAZ003-013-014-020>022-031-032.

     Blizzard Warning from midnight Saturday night to 6 PM CST Sunday
     for IAZ002-003-013-014-021-022-032.

NE...Winter Weather Advisory from noon Saturday to midnight CST
     Saturday night for NEZ013-014.



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