Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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635
FXUS63 KFSD 210458
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1058 PM CST Sat Jan 20 2018

.SHORT TERM...(This evening through Sunday)
Issued at 336 PM CST Sat Jan 20 2018

Complex forecast with strengthening storm system currently taking aim
on the four corners region, moving into the plains on Sunday.  700
mb frontogenesis extending from southwest portion of the state into
the northern portion of the forecast area from Chamberlain to Huron.
 This area could see some light snow developing across the area late
tonight into Sunday.  Expect amounts to be fairly light, with
northeast winds in the near surface layer drawing dry air into the
region. Expect the dynamics to eventually win out, with an inch or
two of light snow accumulating through the day on Sunday.  To the
east along highway 14, expect amounts to be less with the drier air
more pronounced.  Further to the south, expect stratus to work north
from Nebraska. Where the low lying stratus is thick enough, could
get a small amount of drizzle/freezing drizzle during the day on
Sunday.

.LONG TERM...(Sunday night through Saturday)
Issued at 336 PM CST Sat Jan 20 2018

The main show comes in Sunday night into Monday as upper low moves
into the upper Midwest. Overall, models have slowed the progression
of the system slightly, but continue to be very consistent with the
location of the TROWAL setting up across the eastern half of the
forecast area. As upper wave lifts northeast, may see some added
lift from the exiting jet streak over the Great Lakes region, but
expect much of the added broad scale ascent to be associated with
the jet streak extending from Texas into Missouri. With that said,
expect much of the precipitation to be dominated by the low levels-
especially Sunday night. Continuing to see unstable air feeding into
the TROWAL on the 295-300K surface, and am beginning to see small
amounts of CAPE in forecast soundings for Sunday night across
northwest Iowa. Model sounding to the south appear to be fairly
capped, increasing confidence that unstable air will wrap into the
southeast half of the forecast area. LIs are -1 to -2 above 850 mb
across much of the state of Iowa through much of Sunday night into
Monday morning. With this convective environment, could see intense
snowfall rates Sunday night into Monday, with the potential for
thundersnow.

Models are hinting that dry slot may be precariously close to Storm
Lake, making deep saturation a question at this point. Therefore,
amount of icing has increased in this forecast package across our
southeast corner, but confidence is not overly high with this.

Winds continue to look strong with this system as it pulls into the
upper Midwest.  925 hpa winds are 35-45 knots on Monday, suggesting
the potential of blizzard conditions.

With confidence continuing to remain high with the TROWAL, have went
ahead and issued a winter storm warning for the high confidence
locations.  This roughly lies along a line from Yankton to
Worthington-Windom MN, where 10-15" of snow is forecast.  Have also
extended the headlines in time to account for the strong winds that
area expected throughout the day Sunday. Left the watch going on
either side of the warning to account for small scale variations in
the next 24-36 hours. Have also expanded the watch to include Storm
Lake for the potential for icing.

Have not adjusted the extended beyond Tuesday with active weather
in the near term.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1052 PM CST Sat Jan 20 2018

Several concerns through the next 24 hour with a potent winter
storm expected to arrive on Sunday. Light rain and snow will
spread across south central SD into east central SD late tonight
into Sunday afternoon. Additionally, areas in northwest Iowa and
northeast Nebraska could see patchy drizzle develop Sunday
afternoon during the daytime on Sunday. Expect MVFR and IFR
ceilings and visibility to develop in these area during the
drizzle and rain/snow mix, however much of southwest MN into
extreme southeast SD may remain VFR through 00z. Snow will become
widespread across the area late in the afternoon Sunday into
Sunday evening, however areas of northwest Iowa and northeast
Nebraska will likely see a mix of rain, freezing rain, and snow in
the evening hours. North winds are also expected to increase to 15
to 30 kt Saturday afternoon and evening. Widespread MVFR to IFR
conditions are likely in the evening, with LIFR possible at times.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning from 6 PM Sunday to 6 PM CST Monday for
     SDZ062-065>071.

     Winter Storm Warning from 6 AM Sunday to noon CST Monday for
     SDZ050-063-064.

     Winter Storm Watch from Sunday evening through Monday afternoon
     for SDZ040-054>056-059>061.

     Winter Storm Watch from 6 AM CST Sunday through Monday morning
     for SDZ052-053-057-058.

MN...Winter Storm Warning from 6 PM Sunday to midnight CST Monday
     night for MNZ080-081-089-090-097-098.

     Winter Storm Watch from Sunday evening through Monday evening
     for MNZ071-072.

IA...Winter Storm Warning from 6 PM Sunday to 6 PM CST Monday for
     IAZ020.

     Winter Storm Watch from Sunday evening through Monday afternoon
     for IAZ031.

     Winter Storm Warning from 6 PM Sunday to midnight CST Monday
     night for IAZ001>003-012>014.

     Winter Storm Watch from Sunday evening through Monday evening
     for IAZ021-022-032.

NE...Winter Storm Warning from 6 PM Sunday to 6 PM CST Monday for
     NEZ013.

     Winter Storm Watch from Sunday evening through Monday afternoon
     for NEZ014.

&&

$$

SHORT TERM...BT
LONG TERM...BT
AVIATION...



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