Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 092138

Area Forecast Discussion
National Weather Service Sioux Falls SD
338 PM CST Mon Jan 9 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 338 PM CST Mon Jan 9 2017

Quasi-zonal flow continues tonight and Tuesday with one short wave
moving to the I 29 corridor by 12Z Tuesday, followed on its heels by
a second short wave rapidly moving through Tuesday morning and
ushering in a strong surface cold front. In the near term, soundings
are rather moisture starved early this evening, with only a hint of
moisture in our far northern zones, extending into southwest MN
along an 850mb baroclinic zone/frontal boundary. However moisture
does pick up late tonight ahead of the surface front, first in our
northwest zones, then throughout our entire north late tonight and
early Tuesday.

Precip tonight continues to be a real challenge. The model soundings
show primarily sleet in our north and east later this evening, with a
warm and dry layer of air from 850-800mb, but saturation elsewhere
in the sounding plus a very cold dome near the surface. This seeder
feeder mechanism should be able to fall through that thin dry layer
at least by late evening, but QPF amounts are extremely minimal.
Definitely not enough to warrant a winter weather advisory headline
at this time, because there is a huge question that the stratus
depth could very well be overdone on the various models as they were
today and yesterday. If the stratus does not develop this evening in
our north and east, then it will likely be dry.

Now later tonight, moisture depth does increase and saturate up
through a deep layer just ahead of the surface wind shift. Therefore
likely pops are warranted first in our northwest zones around Huron
late tonight, moving across the rest of our northern zones generally
along and north of I 90 toward day break Tuesday. Precip type
continues to look like a wintry mix after midnight due to the
aforementioned soundings described above looking the same, and with
very minimal QPF. But the saturation hits very rapidly, at the same
time wet bulbing down the temperatures aloft to warrant all snow.
Therefore when the precipitation begins in earnest, the precip type
will be primarily snowfall late tonight and early Tuesday which is
why we did not go with a headline at this time. Snowfall amounts of
around an inch to inch and a half could fall along the Highway 14
corridor, with a dusting toward I 90.

Now for areas south of I 90, the moisture profiles are quite weak.
Therefore am mainly concerned about a patchy freezing drizzle threat
along with some light sleet. Amounts will be extremely minor. But
the problem is if this occurs, it will likely be close to the early
Tuesday morning commute to work. But again, if the stratus depth is
overdone by these models, its possible the Yankton, Sioux City and
Storm Lake areas may not hardly get anything at all. So this is all
conditional on stratus, because the mid levels are not extremely
moist. Concerning temperatures, lows tonight will be fairly
seasonably mild for this time of year. But the modified arctic air
will spill in for Tuesday producing only a very minimal temperature

.LONG TERM...(Tuesday night through Monday)
Issued at 338 PM CST Mon Jan 9 2017

The leading nose of the Arctic air settles in on Tuesday, but a
series of weaker waves will keep the southward progression slow.
With this slower progression these weak waves will have a little
thermal band, occasionally within the dendritic layer/s, to promote
some snowfall. For now the better chances Tuesday night should be
along and north of highway 14 while Wednesday night it should be to
the south of Interstate 90. Did lower the lows and highs Tuesday
night into Wednesday north of Interstate 90 as the Arctic air looks
to settle in a little sooner. Also lowered lows Thursday night with
the Arctic high near and overhead.

In the outer periods, Friday through Monday, Arctic high pressure
should be lifting east of the area with a modified cold air mass
over the weekend into Monday. Overall looks like dry conditions but
a few chances for light snow over northwest Iowa through the period
as stronger jet energy moves through parts of Kansas, Nebraska and
Iowa. Temperatures will be quite a bit below normal on Friday still,
but Saturday through Monday will be near to above normal, especially
if we end up getting little to no additional snow cover through the
next few days.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1120 AM CST Mon Jan 9 2017

MVFR conditions lifting north and east of the area early this
afternoon with VFR conditions expected the remainder of the day
through about 6z. After 6z MVFR and likely IFR ceilings will move
back into the area as a cold front moves into the region. By late
Tuesday morning into early Tuesday afternoon it is anticipated
that most of the IFR and MVFR conditions will be east of the area.




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