Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 190537
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1137 PM CST Sun Feb 18 2018

.UPDATE...
Issued at 847 PM CST Sun Feb 18 2018

So far the weather is behaving, throwing no big surprises at us.
Therefore the headlines will remain the same. Did raise pops
overnight in a narrow stripe from south central SD northeastward
toward Brookings for what could be a brief bout of light freezing
rain or light measurable snowfall. Many cams are picking up on
this narrow band in the same area, coincident with strong
800-750mb frontogenesis which is a layer where plenty of moisture
resides.

&&

.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 06Z TAFS through 06Z Monday night)
Issued at 1134 PM CST Sun Feb 18 2018

Overall, conditions should become progressively more MVFR as we
head into Monday morning. There is still a threat for light
freezing drizzle developing in the Sioux City area late tonight
and lingering through most of Monday morning. There is a smaller
threat for freezing drizzle at KFSD early Monday morning. The
precipitation that Huron SD sees should be all snow, with periodic
light snow chances all the way through Monday evening. The
heaviest snowfall in the KHON area should be late Monday afternoon
and evening when IFR visibilities are a threat.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 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 until 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 until noon CST Tuesday for IAZ001>003-
     012>014-020>022-031-032.

NE...Winter Weather Advisory until noon CST Tuesday for NEZ013-014.

&&

$$

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



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