Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 191754
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1154 AM CST Mon Feb 19 2018

.SHORT TERM...(Today and Tonight)
Issued at 311 AM CST Mon Feb 19 2018

As expected, a fairly complicated forecast for the next 24 hours.
Early this morning cold air was surging south and most locations
were between 10 and 20 degrees. The right entrance region of an
upper level jet to the north was interacting with some favorable mid
level temperatures and moisture to allow snowfall to develop in
western and central SD. While the radar is shooting too high to show
it, some light snow has been falling much of the night from Gregory
to Chamberlain to Huron. Likely not much accumulation but the
visibilities have been between 2 and 4 miles. For the most part this
jet remains locked in place for the next several hours and should
continue to produce snowfall in central and northeast SD. Amounts
along highway 14 towards south central SD should be about an inch or
so through this afternoon.

While this jet is producing some snowfall, another southern jet will
race northeast into southern Wisconsin by mid morning. This will aid
in bringing some low to mid level convergence to northwest IA.
Temperatures are not favorable for either freezing rain or snow, so
thinking that precipitation type should be mostly light freezing
drizzle. With this in mind backed off on amounts as a tenth of an
inch of ice by noon with just drizzle seems a bit aggressive.
Regardless, will still be enough ice to cause hazardous conditions
so the advisory still looks good. One concern about icing in this
case is a strong north to northeast wind will cause ice accrual on
one side of objects which can create more problems as the weight of
the ice is not evenly spread across whatever the drizzle is freezing
to.

By late afternoon and early evening another southern jet max lifts
north as the strong right entrance region slowly drifts southeast.
This will likely cause a reenhancement of freezing drizzle across
northwest IA. Model soundings continue to hint at issues with
saturation in the ice bearing layer, but since the sub inversion
temperatures are so cold some ice introduction could occur about 1-
1.5 km above the surface which might allow some snowflakes or very
small sleet to develop.

Farther west the colder air in the mid levels finally starts to
collapse southeast and with the strong jet energy and strengthening
mid level frontal forcing believe that an enhanced band will develop
this evening around the James Valley and shift northeast through the
night. Close to Interstate 29 there are some issues with saturation
aloft in the dendritic layer, but the lower levels indicate plenty
of saturation so believe that at least some small snowflakes will be
likely and will accumulate. Within this band about 3-5 inches of
snow should fall and this band will need to be monitored late this
afternoon as there will be some potential for a small scale band of
6-8 inches, but too early to pick out which 5 or 6 counties would
get that much.

.LONG TERM...(Tuesday through Sunday)
Issued at 311 AM CST Mon Feb 19 2018

By Tuesday there will likely still be some light snow around,
especially in the morning. Some locations could still get an
additional inch or so. Otherwise it will be a cold day with
morning wind chills about 5 below to 15 below and northwest winds
about 10 to 20 mph.

Broad troughing is expected on Wednesday which will keep
temperatures on the cold side and highs from the teens to mid 20s.

The next system of interest will lift northeast on Thursday and
bring a chance for snow back into the area Thursday into Friday. Too
early to tell if it will have much impact but for now looks to be on
the minor side.

As this wave passes milder air will fill in behind and temperatures
will return to something close to normal into the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1153 AM CST Mon Feb 19 2018

North winds will continue throughout the afternoon and evening, with
periods of light snow, light sleet, and freezing drizzle for
locations south and east of KFSD. During the afternoon light snow
will linger in south central South Dakota reaching north and east
toward KHON. The next round of heavier accumulating snow looks to
begin around midnight as the next system moves in from the
southwest. Multiple inches of snow accumulation are likely
throughout the early morning hours for the whole region as a band of
snowfall progresses east. In northwest Iowa, including around KSUX,
isolated thunderstorms with sleet are possible in the middle of the
night, as instability above 6000 ft AGL will support isolated
thunderstorms.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until noon CST Tuesday for SDZ062-066-
     067-070-071.

     Winter Weather Advisory from 6 PM this evening to noon CST
     Tuesday for SDZ038>040-050-052>061-063>065-068-069.

MN...Winter Weather Advisory until noon CST Tuesday for MNZ080-081-
     089-090-098.

     Winter Weather Advisory from 6 PM this evening to noon CST
     Tuesday for MNZ071-072-097.

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.

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...VandenBoogart



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