Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 140925

Area Forecast Discussion
National Weather Service Sioux Falls SD
325 AM CST Wed Feb 14 2018

.SHORT TERM...(Today and Tonight)
Issued at 325 AM CST Wed Feb 14 2018

A quiet morning across the area as southerly winds keep temperatures
relatively mild. There are times when the wind drops off and
temperatures drop to about 10 to 15, otherwise temperatures have
been in the upper teens to around 20. Through the morning and into
the afternoon a trough of low pressure will move through the area,
which will keep a westerly component to the surface wind. This will
aide in providing decent mixing and maintaining dry air.
Temperatures should climb into the 40s in most areas.

By tonight westerly flow will remain in place but weaken. After
what should be a good day of melting fog is expected to develop. The
best chance should be over far southeast SD and northwest IA. Not
expecting widespread dense fog but will be something to watch. Lows
will be on the mild side but with periods when the wind goes calm
expect lows in the teens to lower 20s.

.LONG TERM...(Thursday through Tuesday)
Issued at 325 AM CST Wed Feb 14 2018

The trough of low pressure aloft will shift east on Thursday and
allow cold air to fill in behind. This will cause some non diurnal
temperatures to occur, especially along and north of Interstate 90
as the colder air will begin to work in by late morning and early
afternoon. Aloft a mid level boundary will drop south about the same
time and will support the development of a little light snow.
Forcing not real strong but some locations north of Interstate 90
may see a half an inch. The focus for this development will shift
south and east through the afternoon and evening but lose a little
of its punch, so the chance for measurable snowfall will diminish
across southeast SD and northwest IA.

Thursday night and Friday will be cold with fairly strong northwest
winds and decreasing temperatures. Late Thursday night and early
Friday morning wind chill values will drop to about 10 below to 15
below zero. The cold high pressure will shift south on Friday
afternoon and allow a southerly wind to develop. So, while it will
be colder highs should climb into the teens to mid 20s with some
readings near 30 in south central SD.

Saturday and Sunday will see temperatures climb back above normal.
Saturday is expected to remain dry while Sunday could see a little
afternoon rain or snow shower. Chances not real high right now as
the position of the right entrance region of the upper level jet is
still in question.

Models still in some agreement bringing snowfall potential into the
area. While they agree that there should be a system still not
confident on the details. Overall will be colder to start the week
with a good chance for snowfall, just a little weak on the details.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1053 PM CST Tue Feb 13 2018

Patchy MVFR to localized IFR visibility in fog is possible tonight
through mid-morning Wednesday. Confidence in the favored location
for development tonight is low, so will have minimal mention in
the TAFs at this time.

Any fog tonight should diminish after 15Z, but mild temperatures
leading to snowmelt Wednesday, and light winds Wednesday night,
could result in more extensive fog development beginning near the
end of this TAF period, mainly across northwest Iowa. Confidence
in the timing of development is moderate, so may introduce MVFR
visibility in KSUX late in the TAF period.

Some models indicate a potential for low level wind shear south of
I-90 during the day Wednesday as westerly flow increases atop a
strong inversion maintained by these models. However, current
thinking is the inversion will not be as robust as these models
indicate, and thus will not have any mention of low level wind
shear. Pilots will still want to be aware of a gradual increase in
wind speeds through the lowest 1-2kft.




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