Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 122208
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
408 PM CST Fri Jan 12 2018

.SHORT TERM...(This evening through Saturday)
Issued at 407 PM CST Fri Jan 12 2018

Any lingering pockets of light snow or flurries will come to an end
this evening with passage of reinforcing wave, and continued
influence of low level drying as arctic surface ridge. Does remain
somewhat shallowly dendritic somewhat longer into the night through
the western Missouri River valley until drying below the cloud deck,
so temptation to leave a few flurries into the post-midnight time
frame.

Still concern tonight with wind chills, despite winds being quite a
bit lighter.  Strongest of the oozing gradient will be across
southwest MN into northwest IA where some cold advection likely to
keep a max 7-10 mph wind going much of the night, with otherwise
more of a light north/northeast drainage most areas. Coordinated a
wind chill advisory across southwest MN and eastern portions of
northwest Iowa for wind chills in the 20s below zero, from 03z thru
16z Saturday.  Will be living much of the day Saturday below the
center of the ridge with weak flow, so with sunshine may be a bit
more challenge to warming. Highs should be very close to readings
today. Late in the day, warm advection with wave diving through
western SD and central NE should begin to increase clouds, and could
be enough shallow lift to get a couple of flurries toward evening in
extreme south central SD.

.LONG TERM...(Saturday night through Friday)
Issued at 407 PM CST Fri Jan 12 2018

ALight snow will be possible across mainly southeast SD into the
lower Missouri valley Saturday night as warm advection zone
trudges eastward and wave dives southeast. Best chances will be
through the Missouri River corridor, especially south central SD
from late evening through the overnight hours. Trend has been a
bit more southward with the axis, as digging wave leaves little
enhancement to eastward advancing baroclinicity, thus amounts have
tapered off somewhat from the earlier forecast.

All things withstanding, the big message for the mid range forecast
today centers around the extreme cold. Sunday should be a day or
relative warmth, perhaps above freezing toward south central SD.
However, a strong wave will drop into Minnesota late day, and drive
a very strong arctic front southward into the area during the
afternoon. Trend has been to speed up the passage of the system. At
this point, expecting to find at least some post-frontal snow
showers or flurries for a couple hours behind the boundary as
moisture quickly settles into the dendritic. Possible for many areas
to get a dusting of light snow, which will provide some extra fuel
for blowing snow as winds again increase during the overnight with
passage of a 4-5 hPa/3h pressure rises.  Momentum to mix may be a
bit less than last couple of post frontal events, so more on the
order of 30-35 mph gusts expected.  Winds could easily come up a bit
more as trough transitions to a deep closed low near
Minnesota/Wisconsin.  Wind chills will likely reach -20 to -40,
coldest north of a Huron to Sioux Falls to Storm Lake line toward
Monday morning, with only limited recovery on Monday.  Another
replay of very dangerous wind chills will come on Monday night and
Tuesday morning.  Wind chill warning and advisories will be
certainly be issued as we approach this time.

Have increased clouds on Monday from blends mainly along/east of I-
29, and could very well need addition of a few flurries or snow
showers with deep cyclonic flow in place.

Dry Tuesday with the core of arctic ridge shifting just east of the
area by evening. Slow departure of closed low to the east suggests a
tough exit to the coldest airmass, and enough of a window for a
quicker and more extreme drop during the evening than blended temps,
with developing return flow likely to bring rising temps into
Wednesday morning.

A warming pattern indicated in longer range models for the end of
the week, but no good signal for any organized precipitation. Very
well could be looking at 30s to mid 40s by the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1100 AM CST Fri Jan 12 2018

VFR conditions will prevail through the period, though far
southwest portions of the forecast area could see MVFR ceilings
and/or visibility with a chance of light snow dropping southeast
across the region this afternoon and evening. Clearing expected
for most areas except through the Missouri River Valley for the
latter portion of the period.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...Wind Chill Advisory from 9 PM this evening to 10 AM CST Saturday
     for MNZ071-072-080-081-089-090-097-098.

IA...Wind Chill Advisory from 9 PM this evening to 10 AM CST Saturday
     for IAZ002-003-013-014-021-022-032.

NE...None.
&&

$$

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


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