Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 101202
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
602 AM CST Tue Jan 10 2017

.SHORT TERM...(Today and Tonight)
Issued at 410 AM CST Tue Jan 10 2017

For the most part, it has been a fairly quiet night so far across
the area with only a bit of patchy light freezing rain near the
highway 14 corridor and toward KMWM and the Iowa Great Lakes.
However, things will begin to undergo a rapid change over the next 1-
3 hours as the main trough across the Western Plains begins to pull
eastward.  The main energy in the trough is somewhat split with core
swinging across the Central Plains. A band of light precipitation
developing across Nebraska will stream early this morning into
northwest Iowa. With temps aloft still warm, and surface temps
likely to remain at or just below freezing, likely to produce a
period of freezing rain before more broad lift and bulk cooling
works through the morning to change over to snow by mid morning.
Probably just a couple hours of freezing rain threat, but does not
take much, so have issued a winter weather advisory through the
morning to cover the threat.  Further north across the area,
starting to see a fairly distinct snow band developing across
central South Dakota at 09z along the mid-level frontal boundary,
and it will be this area working eastward that will create a bulk of
the precipitation today. Interesting that there is for the far
northern CWA a signature of neutral to slight negative EPV atop what
is a fairly strong frontogenetic boundary. This suggests that
snowfall could be somewhat significant, if only for a short period
of time during the early to mid morning. Have boosted QPF and
resultant snow amounts a bit, as should not be too much lost to a
brief period of mixed precipitation across eastern SD. Parts of
southwest MN in the warmer airmass could sustain a couple hours of
mix through 7 or 8 am, but again the mass cooling with cyclone
deepening to the south should exercise a fairly quick change over to
snow. Other facet for southwest MN toward the IA Great Lakes area
will be the wind, which will increase to a gusty 25 to 35 mph later
morning through at least mid afternoon. Likely to get some areas of
blowing snow given the current snow cover and expected 1-2 inches
snowfall. Have also issued a winter weather advisory for the mixed
precip to snow threat, adding in mention of blowing snow through mid
afternoon.

Temps seem to be too warm comparing to upstream observations and the
fall which is occurring behind strong cold front now just
approaching the I-29 corridor. Would expect most areas to reach
their highs very early this morning, then fall through most the day
before leveling or perhaps recovering a few degrees, the latter
mainly across the Missouri corridor.

Just when you thought you would be done with wintry precipitation,
the quick zonal pattern will sling yet another weak impulse into the
region tonight. As low level front stall out across Nebraska,
approaching wave will induce a dose of elevated warm air advection
once again by early evening into lower Brule areas, which will
spread east and northeast through the post midnight hours. Will be
some dry air again at lower levels to challenge precipitation, so
have not taken earlier precip beyond a low chance. Temps will ease
into the dendritic range, especially as mid-level front begins to
collapse into areas north of I-90 late Tuesday night. Snow will
become more widespread especially across the far northern CWA near
highway 14 late night.  If was to saturate a bit more to the south,
temps aloft are quite a bit warmer, and would perhaps result in a
narrow freezing drizzle threat closer to the Missouri River valley,
but again have questions on degree of moisture indicated in models
within the intense low level frontal zone.

.LONG TERM...(Wednesday through Monday)
Issued at 410 AM CST Tue Jan 10 2017

Thermal boundary sets up across the forecast area on Wednesday while
a pair of weak mid level waves track east along the quasi-zonal
flow. While moisture remains limited, there will likely be enough
weak forcing for some light precipitation. The initial wave will be
exiting to the east on Wednesday morning, with some light snowfall
ending before midday. The second wave will be quick to follow
Wednesday evening into the early morning hours Thursday, as the
arctic surge pushes further south. Think that the best potential for
any measurable precipitation will be for areas south of I-90, where
some light snow will be possible. Further north, ice crystals may be
absent from the clouds, bringing the threat for some light freezing
rain in the evening before changing to light snow. Think that the
chance of measurable rain or ice in our north is very low. Model
thermal profiles show some significant differences, so confidence is
low at this point.

Strong arctic push arrives Wednesday night into Thursday night, with
a cold surface high drifting southeast through the northern Plains.
With mostly clear skies and a little bit of fresh snowpack,
temperatures will plunge below zero on Thursday night. Good
radiational cooling will drop readings as cold as near 20 below zero
in the highway 14 corridor, while the Missouri Valley will be closer
to zero. Continued the trend of lowering the blend numbers by
nudging 33 percent towards the CMC. It seems very likely that we
will eventually need wind chill advisories or even warnings for late
in the work week.

Fortunately, we are still looking at a warming trend arriving
Saturday into next Tuesday. Weather pattern overall looks pretty
quiet, but the upper level southwest flow could allow a few waves to
clip portions of northwest Iowa. The first would arrive around the
Friday night/Saturday time frame, with the second as early as Sunday
Night. There are much greater model differences with the second
wave, so not a great deal of confidence. However, by Monday and
Tuesday, we do see above normal temperatures return.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 601 AM CST Tue Jan 10 2017

Wintry precipitation creating main aviation issues through the
period. Light freezing rain will prevail across much of northwest
IA, although the threat for KSUX will primarily be through the
first hour of the TAF. Otherwise, a band of snowfall will push
from eastern SD into southwest MN and northwest IA during the
morning. Visibilities will be briefly as low as 1/2 to 1 SM north
of Interstate 90. Ceilings will slide into a period of upper IFR
into lower MVFR as well. With surface winds expected to gust to 25
to 32 knots behind a frontal boundary, areas with existing
snowcover across southwest MN and adjacent locations will likely
find several hours of areas of blowing snow, with visibility as
low as 1/2 to 1 SM. Finally, with shallow colder air in place and
strong off surface warming developing tonight, could see a more
expansive area of IFR or MVFR ceilings develop toward 06z as well
as a band of light snowfall. For now, too low a probability to
specifically mention in TAF for KFSD or KHON.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...Winter Weather Advisory until 3 PM CST this afternoon for MNZ071-
     072-080-081-089-090-097.

IA...Winter Weather Advisory until 3 PM CST this afternoon for IAZ002-
     003.

     Winter Weather Advisory until noon CST today for IAZ013-014-
     020>022-031-032.

NE...Winter Weather Advisory until noon CST today for NEZ014.

&&

$$

SHORT TERM...Chapman
LONG TERM...
AVIATION...Chapman



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