Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 030919
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
319 AM CST Sat Dec 3 2016

.SHORT TERM...(Today and Tonight)
Issued at 318 AM CST Sat Dec 3 2016

Band of low stratus blanketing much of the region is very slowly
eroding along the southwestern edge. With clearing developing across
the Missouri Valley and light winds, patchy fog has developed.
Expect the fog to be very spotty through the early morning hours,
then lift towards daybreak as mid and high clouds increase from the
south.

Potent and fast moving shortwave trough currently in western Wyoming
moves into central South Dakota late this morning. With good forcing
associated with this system and increased moisture advection, expect
light precipitation to develop in south central SD mid morning and
track eastward through the forecast area through this afternoon and
evening. Precipitation type will mainly be light rain or sprinkles,
with temperatures warming into the mid 30s to near 40s in the
afternoon. Subfreezing readings will hold on for much of the day
north of I-90, so expect light snow or a mix of rain and
snow/flurries in these areas. Kept pops in the scattered/chance
range given the very light and spotty nature of the precipitation.
Most areas should see a trace to a few hundredths of liquid, while
snow accumulations will be a dusting at best given the near freezing
temperatures and warm ground temperatures.

Secondary shortwave arrives tonight, close on the heels of the first
wave. Lingering rain across northwest Iowa and southwest Minnesota
this evening will likely switch over to light snow diabatic cooling
drops readings back below freezing. Precipitation will move east of
the region around midnight, while low stratus hangs on in areas east
of the James River. Could see a few light snow showers or flurries
develop near highway 14 late tonight with the trough moving into the
region, but will hold mention to just north of our border at this
time. Lows will be in the mid 20s to near 30.


.LONG TERM...(Sunday through Friday)
Issued at 318 AM CST Sat Dec 3 2016

Sunday into Monday are expected to be mild compared to the remainder
of the week with 925 hpa temperatures at or above 0 C. Westerly flow
is expected to dominate on Sunday behind a weak trough moving
through the region in the morning hours.  Flow will take on more of
a southerly component into Monday ahead of a strong cold front that
is expected to move through on Monday.

Strong winds around 30 knots portended by the ECMWF at 925 hpa
coupled with strong cold air advection will likely result in
stronger winds than in the current forecast in the Tuesday through
Thursday time frame. GFS is substantially slower than the ECMWF in
terms of winds aloft at 925 hpa in the mixed layer, but given the
strength of this system, would prefer to hedge towards stronger
winds, but did not change due to collaboration. Models are
substantially drier with the cold front on Tuesday, suggesting a very
limited amount of precipitation and associated snow cover. Best
chances for accumulating precipitation appears to be across the
north closer to the upper level trough, but even there precipitation
amounts appear to be limited.

Expect a fairly stark contract from temperatures ahead and behind
the cold front.  With that said, have sided with blended
temperatures, since atmosphere will likely be mixy Tuesday-Thursday
with limited snow cover.  Currently have wind chills in the single
digits above and below zero, but these are likely underdone based on
lack of winds in the current forecast.


&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1039 PM CST Fri Dec 2 2016

Stratus quickly sliding northeast as winds aloft are now beginning
to push the low-level moisture axis northeast. Expecting VFR
conditions to arrive at FSD/SUX early this morning, with an
increased risk of fog and stratus in HON. Can`t discount light fog
also forming at the other TAF sites, however southerly winds will
be increasing through daybreak.

Mid-level clouds will persist into Saturday, gradually lowering
through the day. Shortwave trough will pivot into the area late in
the day, and GFS/NAM both showing some potential for light RASN to
fall by mid-aftn along the I-29 corridor. More uncertain is how
low ceilings may fall by the late afternoon and evening hours as
low-level moisture returns.


&&

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

$$

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


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