Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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864
FXUS63 KFSD 111004
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
404 AM CST Sun Dec 11 2016

.SHORT TERM...(Today and Tonight)
Issued at 404 AM CST Sun Dec 11 2016

Snow will gradually come to an end early this morning, as PV
anomaly racing across North Dakota continues to force precipitation
northeast, and wraps drier air southeast into the region.  In all
likelihood, will be able to end winter weather products very near to
daybreak.

Further west, colder air now surging into the Missouri River valley,
as inverted trough slides eastward. Once winds turn to the north or
northwest, temperatures will fall accordingly.  In some areas,
especially east of I-29 falling mid day and afternoon temperatures
are possible. Winds will also increase as the colder air surges
southward.  With gusts up to 25-30 mph minor blowing snow over the
north-south roads will be possible.

By tonight, models suggesting clouds move eastward allowing for
clearing skies and plummeting temperatures especially east of the
James River valley.  Mid-level clouds will be on the increase
towards daybreak, but lows may fall below zero in many locations due
to the fresh snow cover.

.LONG TERM...(Monday through Saturday)
Issued at 404 AM CST Sun Dec 11 2016

Weak surface ridge lagging across parts of southwest MN and
northwest IA in the morning will quickly shift east, as deep trough
pushing along the Canadian border drives a cold front toward the mid-
James valley toward midday.  This front will surge southeast through
the afternoon and early evening, followed by a strong push of arctic
air. Post frontal conditions suggest that will have a good chance
for a few flurries at a minimum, and even a small threat for a
dusting of measurable snow with deep cloud temperatures in the
dendritic range. Post-frontal winds again are not being captured
well by guidance, with isallobaric forcing with pressure rises 5-9
hPa/3h in line with gradient winds of 25 to 35 knots just off
surface. Have again boosted winds into the 20 to 35 mph range for a
few hours, and would have to think there is at least an outside
potential for some spotty blowing and drifting snow from east
central SD into southwest MN late Monday afternoon and Monday
evening. Otherwise, ahead of the arctic front, some sneaky readings
could reach near the freezing point in the lower Missouri valley
where there was more limited Saturday snowfall.

The story for Monday night through Thursday will be the hostile
takeover of cold air through the region. Initial core of high
pressure will rapidly settle into the mid plains by Tuesday morning,
with potential for a period of lighter winds to accompany some
partial clearing.  With chilly readings -14 to -18C at 925 hPa,
would not be shocked to get a few spots dip well below zero.
Albedo will not be our friend to warming on Tuesday, despite the
westerly flow resulting from surface high sinking through the
central plains. By later Tuesday night, will see another impulse
rotating through the mean large scale trough with a reinforcing
arctic boundary dropping across the region. Northwest winds will
become quite blustery, and cannot rule out a couple of flurries
during the day.  By the time the surface ridge settles over the
heart of the area on Thursday morning, should be primed to see temps
drop well below zero, maybe even well below -10 around east central
SD into southwest MN, while the Missouri valley could see readings
hang up closer to zero as high clouds increase the latter half of
the night. There will certainly be periods of wind chills from
-15 to -25 from Monday night through Thursday morning, especially
near/north of I-90.

While there has been some consistency in the presence of a snow-
producing system toward the end of the week and early in the
weekend, there has been little consistency on the structure of such
system.  Solutions currently focus on a complex positively tilted
trough that begins to merge southern and northern stream as it
deepens toward the Great Lakes. Operational 00z GFS and EC actually
develop quite a cyclone moving northeast through Iowa around Friday
night.  Have topped out PoPs at likely levels for the time being,
but from the warm advection wing lifting through later Thursday
until the wrap around frontogenesis on early Saturday, there should
be a fairly decent precipitation chance somewhere across the area.
Temperatures would be likely to moderate some Thursday night into
Friday evening, before developing system pulls down much colder air
once again for the weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1105 PM CST Sat Dec 10 2016

Widespread MVFR-IFR ceilings/visibility will persist through
tonight, with occasional LIFR visibility at times in heavier snow
bands, most likely from east central SD into southwest MN. Exception
to the sub-VFR conditions will be near the Missouri River Valley
where snowfall will be more limited and VFR conditions more
prominent. Gradual improvement from southwest to northeast is
expected through the late morning and afternoon hours on Sunday.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 9 AM CST this morning for SDZ056.

     Winter Storm Warning until 9 AM CST this morning for SDZ040.

MN...Winter Weather Advisory until 9 AM CST this morning for MNZ080-
     081-097.

     Winter Storm Warning until 9 AM CST this morning for MNZ071-072.

IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...Chapman
AVIATION...JH



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