Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 130349
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
949 PM CST Thu Jan 12 2017

.UPDATE...
Issued at 946 PM CST Thu Jan 12 2017

Boosted pops to likely right along the I 90 corridor from
Chamberlain to Rock County Minnesota Friday morning. Latest NAM
shows very deep saturation in that area with decent dendricity to
aid in the efficiency in snowfall production. Still looks like
less than an inch of snow however even in the likely area. But
would not rule a half inch to three quarters of an inch.

&&

.SHORT TERM...(This evening through Friday)
Issued at 325 PM CST Thu Jan 12 2017

After the passage of a weak cold front, Arctic high will settle into
the area tonight. Winds will start waning down late in the evening,
but temperatures will continue to fall through around midnight.
Temperatures rise gradually after 06z with the increase of clouds
from the southwest. Wind chills are expected to fall to 20 below to
30 below tonight, with the coldest readings around 06z. Lowest
readings are likely across southwest Minnesota, and areas along and
north of Highway 14. A wind chill advisory will be issued from 00z
tonight to 13z Friday.

Behind this Arctic high, unsettled weather conditions return again
across the area early Friday morning. As the Arctic air moves
northeast, an area of warm and more moist air will be advecting
northward, increasing risk of precipitation, with thermal profiles
suggesting all snow. Given that dry air from the Arctic ridge in the
northeast area will persist, snow will have difficulties to keep
developing across southwest Minnesota. Higher chances will occur in
the morning along and west of the James River. In terms of snow
amounts, less than a half inch is possible in most areas.

.LONG TERM...(Friday night through Thursday)
Issued at 325 PM CST Thu Jan 12 2017

Relatively quiet first half of the weekend with zonal flow resulting
in near seasonal temperatures.

Southerly flow develops on Sunday with saturation deepening
throughout the day. Models are suggesting a cold layer near the
surface with warm layer near 850 mb developing aloft.  12Z suite of
models are starting to align resulting in greater confidence in
track of the system.  With that said, degree of warming aloft is
still inconsistent, with the ECMWF running 2-3 degrees C warmer than
Canadian/GFS.  Have begun to raise wet bulb aloft to increase areal
coverage of icing potential Sunday night into Monday.  Appears the
greatest threat will be ahead of inverted trough type feature that
appears to set up near the James River Valley, and shift east
throughout the day on Monday. Models differing on the amount of
cooling behind the trough, but all suggest a transition to snow on
the backside of this system.  With coordination, have issued a
Winter Storm Watch for the southern most tier of counties across
northeast Nebraska into northwest Iowa.

Chinook pattern develops mid week next week resulting in mild
temperatures expanding east of the Rockies. Still may be a struggle
to warm too much above average across the eastern half of the
forecast area-as mixing will be fairly limited. If we are able to
draw the warm air aloft to the surface, potential exists for warming
well above normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 533 PM CST Thu Jan 12 2017

The main issue with aviation through late Friday is the timing of
the next weak disturbance which will bring light snow to the
forecast area on Friday. The various models are all in good
agreement in showing a 2 or 3 hour window of snowfall, with the
timing reflected in the TAFs. The primary concern during the
snowfall is MVFR to IFR conditions. At this time, LIFR does not
look like it will occur.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Chill Advisory until 7 AM CST Friday for SDZ038>040-055-056.

MN...Wind Chill Advisory until 7 AM CST Friday for MNZ071-072-080-081-
     089-090-097.

IA...Wind Chill Advisory until 7 AM CST Friday for IAZ002-003.

     Winter Storm Watch from Sunday afternoon through Monday evening
     for IAZ031-032.

NE...Winter Storm Watch from Sunday afternoon through Monday evening
     for NEZ013-014.

&&

$$

UPDATE...MJ
SHORT TERM...JH/JM5
LONG TERM...BT
AVIATION...MJ



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