Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 150510 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Sioux Falls SD
1110 PM CST Sat Jan 14 2017

.SHORT TERM...(This evening through Sunday)
Issued at 335 PM CST Sat Jan 14 2017

Quiet weather in store this evening through much on Sunday, ahead of
the upcoming storm system. Temperatures have warmed nicely this
afternoon, with broad surface high pressure overhead bringing light
winds and ample sunshine. Light and variable winds continue into the
overnight hours, gradually becoming light from the south around
daybreak. Overnight lows will be fairly tricky with light surface
winds, mostly clear skies, but milder warm air advection. Went with
similar readings to last night`s lows, dropping temperatures
slightly towards colder guidance in the Huron through Brookings
corridor where snowpack is a little more substantial. Lows will
mainly be in the single digits above zero.

Southerly flow increases on Sunday, taping into warm air advection
and increased moisture through the day. Clouds will be on the
increase from the south in the afternoon, but general model
consensus indicates that any precipitation will hold off during the
afternoon. Temperatures on Sunday will be quite mild, especially in
the Missouri Valley where readings near freezing will be possible.
Elsewhere, highs will be in the mid 20s to near 30.

.LONG TERM...(Sunday night through Saturday)
Issued at 335 PM CST Sat Jan 14 2017

Medium range continues to focus on winter storm that is expected to
impact the Midwest Sunday night into Monday.  System is currently in
the Baja of California, and is expect to lift northeast into the
Midwest over the next 24 hours.  Ahead of the wave, there is strong
moisture advection resulting around 850 hpa wet bulb temperatures
remaining above freezing across at least the eastern half of the
forecast area. With isentropic lift increasing as the wave lifts
northeast, expect precipitation to develop and lift north through
the area Sunday night into Monday morning.  Strongest lift on 290K
surface begins in earnest around 09Z Monday morning.  Models at this
point are differing greatly in precipitation amounts, with the ECMWF
and GFS remaining on the low side of amounts and the NAM forecasting
nearly a half of an inch. After coordination with surrounding
offices, ended up blending Superblend QPF amounts with WPC amounts
which favored a 00Z EC/UkMet and 12Z GFS blend. Overall, this slowed
the advancement of QPF slightly, and placed a greater emphasis on
the 18-00Z time frame Monday across northwest Iowa. This is not to
take away from the 12-18Z QPF, as it is the time period when
widespread icing is most significant.

Have also raised pops significantly through the duration of the
event.  Significant questions still remain however.  Interaction
between the southern stream system and shortwave cutting across in
the northern branch of the jet remains uncertain, affecting both QPF
amounts and precipitation type with each solution.  As such, have
only upgraded most confident area for significant icing into an ice
storm warning. This is not to say that those areas will be snow
free, but the ice will be the primary element creating the greatest
impact. Further to the north, there will be a combination of ice and
snow as the cooler air works in from the west, but how quickly the
change over occurs is still murky. Still looks like the potential
for a swath of 2-4" of snow on the northern edge of the heaviest

With the focus on the late weekend storm, have not made any changes
to the extended, but does appear to be much warmer late in the week
ahead of another approaching system next weekend. For now, have not
adjusted pops, but models have been fairly consistent with this
system, so will likely have to raise pops in future forecasts.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1102 PM CST Sat Jan 14 2017

VFR conditions and light winds are expected for most areas through
16/00Z. Exception will be some MVFR-IFR visibility in areas of BR
across parts of northwest IA/southwest MN through shortly after
daybreak Sunday. Some models also hinting at MVFR visibility
working into the Interstate 29 corridor from KFSD-KBKX, so will
carry a mention of this at KFSD during the pre-dawn hours.

Lowering ceilings will spread into the region from the south
after 16/00Z, with MVFR ceilings becoming more likely toward the
KSUX area late in this TAF period, as wintry precipitation develops
northward through eastern Nebraska. This precipitation, most likely
FZRA, could also impact KSUX as early as 16/03Z. However confidence
in this timing is low, so opting to leave precipitation mention
out of this TAF issuance.


SD...Winter Storm Watch from Sunday evening through Monday evening
     for SDZ068>071.

     Winter Storm Watch from late Sunday night through Monday evening
     for SDZ062-066-067.

MN...Winter Storm Watch from late Sunday night through Monday evening
     for MNZ080-081-089-090-098.

IA...Winter Storm Watch from Sunday evening through Monday evening
     for IAZ012-013-020.

     Winter Storm Watch from late Sunday night through Monday evening
     for IAZ001>003.

     Ice Storm Warning from 9 PM Sunday to midnight CST Monday night
     for IAZ014-021-022-031-032.

NE...Winter Storm Watch from Sunday evening through Monday evening
     for NEZ013.

     Ice Storm Warning from 9 PM Sunday to midnight CST Monday night
     for NEZ014.



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