Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 240435
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1035 PM CST Mon Jan 23 2017

.SHORT TERM...(This evening through Tuesday night)
Issued at 315 PM CST Mon Jan 23 2017

SNOW!!  Short term forecast is focused on upcoming winter storm to
impact the area on Tuesday.  150+ knot jet oriented across the
central plains will place the region in jh left exit region
providing enhanced lift in the upper levels.  Closer to the surface,
will be dealing with a bit of dry air initially, but as the wave
currently across Central Utah lifts north, expect precipitation to
begin to develop across the area.  Expect precipitation to be light
initially, but could be a bit of a mix in south central South Dakota
early as precipitation falls into dry but warm layer.  Expect
profiles to quickly wet bulb below freezing, making this a snow event
across the entire area.

Snow ratios appeared to be too low across the region, especially
across northwest Iowa and therefore blended the NAM/GFS into snow
ratios.  Overall, expecting a fairly wet snow with ratios varying
from 10-14:1.  For QPF placement, followed 750 mb frontogenesis,
which is still not precisely defined amongst the various solutions.
The GFS continues to favor the further north track, with the
Canadian and ECMWF focusing further to the south. Blended WPC which
favored a UKMET/Ecmwf blend, which seemed to be near the mean of
the 750 hpa frontogenetic placement. Frontogenesis really
increases in intensity Tuesday at 18Z and remains strong through
00-03Z time frame Wednesday. At that time, a second, albeit
weaker, band attempts to form to the south and east of the main
band, potentially reducing the remaining effects of the initial
band, but this will be a gradual process. Expect the heaviest
snowfall to develop with the initial primary frontogenesis band,
developing in the mid morning hours along the South
Dakota/Nebraska border, then expanding north and east and
lingering along I-90 through the evening hours on Tuesday.

In terms of amounts, appears as though there will be a solid 2/3 to
1 inch of QPF south of I-90, with locally higher amounts.  Did not
go as high as NAM, which locally produced 1.5" across northwest
Iowa. Would think locally amounts around a foot are possible-
especially south of I-90 across far southeastern South Dakota into
Northwest Iowa. Have a widespread 8-10" forecast across the area,
with locally higher amounts.  As such, have upgraded the entire area
into Winter Storm Warning.

Winds will increase across the area as the wave deepens Tuesday
afternoon into Tuesday night. With relatively wet heavy nature of
the snow, am not expecting significant blowing and drifting of the
snow once it has fallen.  If blowing becomes more of a problem, will
need to extend the warning in time to include the daylight hours on
Wednesday.

.LONG TERM...(Wednesday through Monday)
Issued at 315 PM CST Mon Jan 23 2017

Upper level trough continues to pull away to the northeast Wednesday
morning, with lingering light snowfall ending from west to east
through midday. Breezy northwest winds are expected throughout the
day, with gusts to 30 mph likely. Given the heavy, wet nature of the
snowfall, blowing snow concerns will be minor, however cannot rule
out some drifting over roadways or localized visibility reductions
in open areas. Expanded the area of patchy blowing snow. Highs will
reach the mid 20s to near 30.

Northerly flow on Thursday through Sunday will tap into colder air,
however the airmass is not particularly frigid. Each day the airmass
will modify slightly, with highs in the low to mid 20s on Thursday,
warming into the mid 20s to mid 30s by Sunday. Several weak
shortwaves drops southward during this time fame, but overall the
forecast is mostly dry. With the periodic shortwaves and stratus,
there will likely be some spotty flurries at times, but given the
low potential, uncertain wave timing, and the ongoing focus on the
upcoming heavy snowfall, will leave out mention for now.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1033 PM CST Mon Jan 23 201705

A distinct slowdown in the approach of this system is evident.
Trending deeper and further refined by dry air intrusion from the
northeast, have trimmed snow chances back until the afternoon at
Sioux Falls and Sioux City.

The exact track and northern extend of the snow band is still in
question. Some solutions only bring the band up to or just north
of I-90. If snow does reach the area in the afternoon, expect very
drastic changes in conditions towards LIFR and VLIFR into the late
afternoon and evening hours.

Snow will continue through the overnight as winds turn
northwesterly after midnight.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning from 6 AM Tuesday to noon CST Wednesday for
     SDZ040-055-056-061-062-066-067-070-071.

     Winter Storm Warning until 6 AM CST Wednesday for SDZ038-039-050-
     052>054-057>060-063>065-068-069.

MN...Winter Storm Warning from 6 AM Tuesday to noon CST Wednesday for
     MNZ071-072-080-081-089-090-097-098.

IA...Winter Storm Warning from 6 AM Tuesday to noon CST Wednesday for
     IAZ001>003-012>014-020>022-031-032.

NE...Winter Storm Warning from 6 AM Tuesday to noon CST Wednesday for
     NEZ013-014.

&&

$$

SHORT TERM...BT
LONG TERM...
AVIATION...Dux


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