Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 182341
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
541 PM CST Sun Feb 18 2018

.SHORT TERM...(This evening through Monday)
Issued at 400 PM CST Sun Feb 18 2018

Winds this evening will begin swinging around to westerly and then
northerly as the strong low pressure system, which brought this
morning`s winds, exits to the east.

North winds overnight will bring in shallow, cold air near the
surface. As the upper-level longwave trough located over the Western
CONUS slides east, its associated surface low pressure will move
northeast across Kansas into Iowa. This system will advect and
lift moist air around the eastern and northern side of the low
pressure center, bringing a wintry mix of precipitation to most of
northwest Iowa, portions of southern Minnesota, and the Sioux
City vicinity during the early morning hours. Precipitation type
will likely begin as freezing drizzle before changing over to
sleet as the lowest saturated levels of the atmosphere cool below
-10 C. Total ice accumulation looks to be as high as around 0.1
inches around Storm Lake and Spencer, but any sleet mixing in
would lower this total. Nevertheless, those in northwest Iowa,
southern Minnesota, and the Sioux City area will want to plan for
extra travel time, as any amount of ice accumulation can quickly
cause traffic issues. Winter Weather Advisories overnight into
Monday cover this hazard.

Meanwhile, along a Lake Andes to Brookings line, light snow will
begin overnight and continue through noon Monday with accumulations
ranging between 1 to 2 inches. Places like Yankton to Sioux Falls
may only see a dusting through noon Monday, as this corridor will
sit between systems for the first round of winter weather.

.LONG TERM...(Monday afternoon through Sunday)
Issued at 400 PM CST Sun Feb 18 2018

The second round of complex winter weather begins Monday afternoon
and evening lasting through Tuesday morning. A strong shortwave
embedded in the jet stream will swing northeast through the region
providing lift for additional snowfall. This snow should amount to
several inches for most locations in the tri-state area, prompting
additional Winter Weather Advisories which run through Tuesday
morning. Some banding is possible with robust mid-level frontal
dynamics, so snow totals will vary, but 2 to 4 inch amounts should
be common by Tuesday afternoon. Again, northwest Iowa will likely be
a special case, as limited saturation in the dendritic growth zone
will again lead to little snowfall, but instead bring the threat of
light freezing drizzle and sleet. Another light coating of freezing
drizzle mixed with sleet is likely overnight into Tuesday morning.

Tuesday evening, the winter weather systems will move out of the
area, leading to a chilly Wednesday as a cold and dry Canadian
surface high pressure build into the area. As the high pressure
exits Thursday, southerly flow could bring additional moisture and
snowfall into the region, but models still have vast differences in
timing these the shortwave troughs that provide the lift necessary
for snow. No model shows major a major system, but all hint
continued active winter weather, so the end of the week could again
have periods with winter driving conditions.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 536 PM CST Sun Feb 18 2018

Confidence is low with the 00Z TAF set with the details of
expected timing of precipitation and arrival of MVFR or IFR
ceilings. Currently behind a cold front, KHON has turned to MVFR
with some VFR noted upstream in parts of northeast SD and
southeastND. So although MVFR should be the dominant category
tonight at KHON, would not be surprised to see some VFR conditions
at times. Otherwise light snowfall should set in at Huron SD late
tonight and Monday, possibly producing IFR visibilities by late
morning Monday. The arrival of stratus at KFSD and KSUX is a real
question mark. MVFR stratus should advect down from the north as
the cold air punches in behind the cold front, but in the shorter
term, freezing drizzle could move into KSUX late tonight lasting
through Monday morning. Light freezing drizzle or light snow is
also possible at KFSD on Monday. Will continue to monitor for
trends of stratus arrival at KFSD and KSUX and alter if needed.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from midnight tonight to noon CST
     Tuesday for SDZ070-071.

     Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for
     SDZ038>040-050-052>069.

MN...Winter Weather Advisory from midnight tonight to noon CST
     Tuesday for MNZ081-089-090.

     Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for
     MNZ071-072-080-097-098.

IA...Winter Weather Advisory from midnight tonight to noon CST
     Tuesday for IAZ001>003-012>014-020>022-031-032.

NE...Winter Weather Advisory from midnight tonight to noon CST
     Tuesday for NEZ013-014.

&&

$$

SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...MJ



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