FXUS63 KFSD 181120

Area Forecast Discussion
National Weather Service Sioux Falls SD
520 AM CST Fri Jan 18 2019

.SHORT TERM...(Today and Tonight)
Issued at 248 AM CST Fri Jan 18 2019

The well advertised impactful snow producing system is evident on
satellite imagery early this morning exiting the Rockies with
blossoming radar returns across the central and western Dakotas.
The main/parent upper level forcing/Div Q, along with the main
surface reflection will pass well to the south of our region.
Meanwhile, several other forcing mechanisms will/have come
together to provide snowfall for our area. At a large scale
perspective, an incoming secondary vort max along with the favored
right entrance region of the northern stream jet max will provide
broad lift across the region. Additionally, good isentropic lift,
especially from around daybreak thru early/mid afternoon is also
noted. At a somewhat finer scale, a band of mid level
frontogenesis is ongoing across central SD and will pivot east,
northeastward and fade, with a new area developing along the I-90
corridor into our northern counties of NW Iowa by mid to late
morning. With increasingly deep dendritic profiles thru the day,
expect very favorable conditions for snow across much of our
coverage area thru the day.

Snow Amounts/Rates: With all of the above mentioned factors, expect
fairly healthy snow amounts across much of the region, generally in
the 4 to 8 inch range. Wouldn't rule out a few isolated higher
amounts if any heavier banding can become more persistent and
focused on any one particular area. Also expect rates to be fairly
stout at times from mid morning thru mid afternoon, perhaps around
or over 1 inch an hour. As omega in the dendritic zone fades thru
the afternoon, expect snow rates to do the same.

Have some concerns about snow amounts over a couple of different
areas given latest model trends. The biggest concern is across my
far southern areas along the MO River and then Woodbury and Ida
counties in Iowa, including Sioux City. Latest models struggle to
bring the main band of snow far enough south until the afternoon
hours, thus missing out on several hours of good accumulating
snow. Trended snow amounts downward in these areas and will need
to monitor trends thru the morning hours.

Headlines: Only change to the headlines with this forecast package
was to add Kingsbury and Brookings counties to the Winter Storm
Warning with new snow amounts sneaking just over the criteria
threshold. As mention above, will need to monitor some of our NW
Iowa counties that are currently in the warning for any additional
downward trend in amounts. Even our bottom row of SD counties in
the warning may struggle to reach criteria.

Impacts: While not expecting significant wind with this system,
the light, fluffy nature of the snow won't take much to blow
around. Could see some northeasterly gusts in the 20-25 mph range.
With the rate of snowfall, visibility will also be reduced at
times and snow-covered roads will lead to difficult travel

.LONG TERM...(Saturday through Thursday)
Issued at 248 AM CST Fri Jan 18 2019

As snow comes to an end Friday night, surface high pressure will
build in with NAEFS guidance indicating surface high pressure values
in the upper 90th percent of climatology. This will allow very cold
air to pour into the region. Saturday morning wind chills will range
from -15 to -25, with some areas north of I-90 likely nearing or
exceeding advisory criteria. With a fresh snow cover in place,
nudged Saturday afternoon high temperatures down a shade with most
locations stuck in the single digits.

Next wave and push of mid level warm advection moves in late
Saturday night into Sunday morning. This looks to provide another
quick shot of light snow to our SW Minnesota counties, although
amounts currently look pretty light.

Another more burly wave approaches later Monday into Tuesday.
Quick glance at the forecast soundings show lower levels may work
towards saturation during the afternoon hours before the ice
growth zone does and thus may start as a wintry mix before
switching to snow. Amounts don't look too impressive at the moment
but winds could play some factor. Bumped winds up a bit over
blended guidance.

Behind this system, will see another round of colder air pour into
the region. With upper level northwest flow setting in, will likely
see periodic passing disturbances.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 510 AM CST Fri Jan 18 2019

Winter storm starting to settle into the region with snow rapidly
expanding. In addition to the MVFR to IFR ceilings, expect IFR to
LIFR visibility to develop during the heavier snow rates,
especially at KHON and KFSD. Additionally, breezy northerly to
northeasterly winds gusting in the 25-25 kt range will also lead
to issues with blowing snow. Snow will begin to taper off from
west to east thru the late afternoon and evening hours with
improving visibilities. Lower ceilings will linger until late in
the TAF period.


SD...Winter Weather Advisory until midnight CST tonight for

Winter Storm Warning until midnight CST tonight for SDZ066-067.

Winter Storm Warning until 6 PM CST this evening for SDZ038>040-

Winter Storm Warning until midnight CST tonight for SDZ056-062.

Winter Weather Advisory until 6 PM CST this evening for SDZ050-

MN...Winter Storm Warning until midnight CST tonight for MNZ071-072-

IA...Winter Weather Advisory until midnight CST tonight for IAZ020-

Winter Storm Warning until midnight CST tonight for IAZ001>003-

Winter Storm Warning from 9 AM this morning to midnight CST
tonight for IAZ013-014-021-022-032.

NE...Winter Weather Advisory until midnight CST tonight for NEZ013-



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