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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
257 PM CST Monday Dec 22 2014

Short term...(this evening through tuesday)
issued at 256 PM CST Monday Dec 22 2014

Messy forecast through the next day as surface low pressure moves
from the eastern Dakotas towards the western Great Lakes.
Currently...surface cold front aligned along the I-29 corridor is
slowly shifting east. Along and ahead of the front...visibilities
are tanking under light easterly flow...and with the front expected
to make little headway through 06z...expect low visibilities and fog
to become more widespread across southwest Minnesota through the
evening hours. As the low pressure system shifts east...expect
winds to become more northeasterly allowing visibilities to improve
some after midnight. Trowal sets up west of the forecast area
tonight and shifts east through the forecast area late tonight into

This system is struggling from a lack of cold air...and as such have
snow water equivalents around 10-12 to 1. Have the heaviest
accumulations across south central South Dakota...with a widespread
1-3 inches of snow across much of the remainder of the forecast
area. With minor amounts of snow...have continued to keep forecast
area headline free. Complicating factor will be the strong
northwest winds that develop through the day on Tuesday. With the 30-
35 knots of flow at 925 hpa and weak cold air advection in the low
levels... northwest winds should hover in the 15-30 miles per hour range much
of the day. Cold air advection increases late tomorrow the trowal winds down...and with the strong gradient
across the area...could see winds increase slightly on the backside
of the band. In terms of temperatures...have warmed forecast some
both tonight into tomorrow with lack of cold air wrapping into the
system. Expected very little in the way of diurnal range on

Long term...(tuesday night through monday)
issued at 256 PM CST Monday Dec 22 2014

Lingering light snow likely in the eastern County Warning Area Tuesday evening but
drying aloft will work in through the night which should bring an
end to the light snow. Otherwise cold and breezy with partially
clearing skies. Will need to keep an eye on trends with sky cover as
clearing may be more pronounced with fairly cold dry air working in.
For now looking at upper teens in central South Dakota to middle 20s from
Interstate 29 east.

A quick moving ridge of high pressure will swing through on
Wednesday which will keep winds a little lighter. Expecting high
mainly upper 20s to middle 30s.

Thursday looking pretty quiet as well as low pressure develops to
the southwest of the area ahead of incoming upper level wave. We
could see some light snow develop in the far northwest corner of the
County Warning Area on Tuesday afternoon with increasing chances for snow Thursday
night. The models are in much better agreement with this energy so
increasing probability of precipitation and increasing snowfall amounts a bit. Mainly
looking like a fast moving 1 to 3 inches at this time.

In the outer periods(friday through monday)...persistent troughiness
will keep a busy pattern in place. The models are in much better
agreement today with the system on Friday so will increase probability of precipitation a
bit there. After this wave passes weak ridging is expected to
develop as another jet maximum dives into the western United States.
This energy is expected to begin spreading across the plains late
Sunday night into Monday. Right now it appears the the northern
stream will be too strong to allow the digging West Coast trough to
eject northward so not planning on a whole lot of accumulation. One
trend though will be below normal temperatures through the
period...especially if we have some fairly fresh snow cover from
tonight into Tuesday as well as the system Thursday night into


Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1135 am CST Monday Dec 22 2014

IFR conditions expected through the period as cold front moves
through the region and precipitation changes from rain to snow.
Greatest reductions to visibility due to snow expected after 06z
tonight...into Tuesday. Northwesterly winds will also increase
through the overnight into Tuesday...creating the potential for
blowing snow.


Fsd watches/warnings/advisories...
South Dakota...none.


Short term...chenard
long term...08

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