Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 111200
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
600 AM CST Wed Jan 11 2017

.SHORT TERM...(Today and Tonight)
Issued at 331 AM CST Wed Jan 11 2017

Precipitation timing and location continues to be the significant
short term challenge.  The next 24 hours will be largely impacted by
presence of mid-level baroclinicity and several subtle impulses
moving along a strong and confluent steering flow.

Leading wave has quickly exited in these overnight hours and left
quiet conditions in place. Another weak impulse will scoot through
the region early this morning, helping to drive southward the cold
air massing over northern portions of the region. Leading edge of
the cooling is an inverted trough, which has been sharpening from
northeastern Nebraska into northwest Iowa in the post midnight
hours.  Broad area of light snowfall across western toward central
SD early this morning will generally follow the progression of mid-
level frontal boundary slowly south and east, but will gradually
work to encounter some drying undercutting the precipitation as it
streaks eastward, mainly through areas north of I-90. Amounts light
on any regard late night into early this morning, only a couple or
three tenths at most.

Much of the midday will likely be quiet from a precipitation
standpoint, or perhaps limited to a whisper if one considers temps
remaining in the dendritic growth range and threat for a couple of
flurries. By late afternoon, approach into the western plains of yet
another weak wave will start to increase mid-level frontogenetic
forcing. Light snowfall will stream into south central SD by mid
afternoon, and perhaps reach I-29 toward 6 pm. Going through the
evening, a pretty solid signal of existence on all models, with
variation as to the latitudinal track through the CWA.  As a result,
have increased chances into categorical to likely in much of
southeast SD, but models pretty much showing a bit more difficulty
to maintaining the band further east into the lower level dry air
where have trended PoPs down a bit over those earlier in the night
and further west. Snowfall should vary from a half inch or less
toward Highway 14 and the Iowa Great Lakes to perhaps an inch to
inch and a half around lower Brule areas.

Temps at 3 am mainly single digits I-90 and north, working through
teens south of I-90 to some lower 20s ahead of the feature around
KSUX. Lower 30s not all that far away across eastern Nebraska and
western Iowa, and will be a race to see if trough collapses southward
faster than warming can occur with very mild readings aloft across
northwest Iowa early today. For most areas, have highs not far from
current overnight readings as will be a struggle to overcome the low
level cold advection driving readings down this morning, just to get
back to where we are now. Those in northwest Iowa will likely not
recover to where late night temps climb. Lots of clouds overnight
and slight warming of temps aloft will keep from too much of a
plummet, mainly mid single digits below zero north to lower single
digits below south.

.LONG TERM...(Thursday through Tuesday)
Issued at 331 AM CST Wed Jan 11 2017

The main focus in the medium range will be on temperatures early in
the period, with eyes on a potential storm system for early next
week.

Thursday-Thursday Night: High pressure will race into the area
during the daytime hours, behind a secondary surge of colder air
expected in the afternoon. Temperatures should quickly fall after
sunset as winds turn light and skies are mostly clear.  As minor
shortwave ridging moves into the region, we should see a marked
increased in mid and high level clouds after midnight and especially
by daybreak Friday. Clouds may lead to a non-standard diurnal curve,
but given expectations of a fall into double digit below normal
temperatures, wind chill advisories will be needed.

Friday: Compact shortwave energy slides through the Dakotas on
Friday.  Lift with this subtle system remains rather strong, but a
lack of substancial moisture keeps this system from producing higher
snow amounts.  Instead, a very light snowfall again crosses the CWA
by Friday afternoon with accumulations less than one half inch.

This weekend: A bit of a split flow pattern develops this weekend as
energy drops into the Southwestern US. Broad ridging should help
warmer low level air build into the region resulting in warming
temperatures by Sunday. Dry conditions are anticipated with no
strong winds.

Monday-Tuesday: A very uncertain pattern evolving to start next week
as models continue to struggle with the general evolution and track
of a low eventually residing in the Southwestern US. Recent model
trends have pushed the track of the mid-level low further north.
Although ECMWF and GFS remain far apart in their specific
solutions,the general consensus brings increased risks of
precipitation by Monday and into Tuesday. Given the anomalous 850
meridional flow with this system, and generally increased low-level
thermal temperatures due to overarching synoptic ridging, there will
be an increased risk for mixed precipitation over NW Iowa and
adjacent areas. Still a bit too far out to get into any specifics,
and with the high likelihood that model guidance will continue to
have high run-to-run variance, best advice is to continue to monitor
the forecast.

After Tuesday, all signs point to warmer temperatures into next
week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 558 AM CST Wed Jan 11 2017

MVFR ceilings will persist for a time behind frontal boundary
which is drifting through northeast Nebraska and northwest Iowa
just before 12z. Band of snowfall will feature spotty MVFR
visibilities as well, but trend should be gradually higher with
ceilings as drier air undercuts, as well as less with coverage of
snow heading toward late morning. Another disturbance moving in
from the west will regenerate yet another light snow band tonight
with MVFR ceilings and likely areas of MVFR to briefly IFR
visibility.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

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



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