Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 171119
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
619 AM CDT Tue Apr 17 2018

.SHORT TERM...(Today and Tonight)
Issued at 334 AM CDT Tue Apr 17 2018

Another cold April night across the region as temperatures have
fallen into the teens and 20s.  Today will be another cool, but
quiet day across the region, as we wait for our next dose of winter
weather later tonight and into Wednesday.

Today: With high pressure settling just east of the forecast area
today, winds will gradually turn to the east.  Temperatures may
reach into the 40s, despite the widespread snow, because of a mid-
April sun.

Tonight:  Models have come into better agreement on the track of our
next winter system that arrives late tonight into Wednesday.  GFS
has shifted slightly further south to match the track of the
ECMWF, and most other models are also in reasonable agreement,
producing the highest QPF over northwest and northern Iowa. In
general models have slowed down the arrival of precipitation by a
couple hours.

Anticipated precipitation to break out quickly this evening, as
warm advection process and strong dynamics from the slightly
negative tilted trough move into the region. Have blended QPF
slightly with CAMs overnight, which do produce slightly higher QPF
amounts along the mid-level diffluent axis across the central
parts of South Dakota towards the James River Valley.

There could be a very brief wintry mix as precipitation starts and
soundings saturate initially, with a quick turn to snow after that.
However a stubborn warm layer over northwest Iowa may allow a
more prolonged mixture of rain, sleet and low end freezing rain
for the initial surge of precipitation that moves through. While
QPF is higher in NW Iowa, some of this may go to a few tenths of
an inch of sleet and up to a tenth of an inch of freezing rain.
Also present in soundings from the NAM/GFS is a layer of elevated
instability that pivots northwest ahead of the upper low. Most
predominantly found in above the 750 mb layer, there could be
just enough instability present to produce isolated to scattered
lightning.

.LONG TERM...(Wednesday through Monday)
Issued at 334 AM CDT Tue Apr 17 2018

Wednesday: The good thing about this system is that it`s fairly
progressive in nature, with a fast moving band of snow moving
northeast during the morning hours. Snow will end from southeast to
northeast through the day, with snow lingering slightly along the
Buffalo Ridge in the afternoon as the system takes more of a
longitudinal wobble.

Overall, widespread amounts between 2 and 6 inches are again likely.
 The greatest risk for seeing just above warning level snows exists
over the far eastern zones. However, factoring potential for mixed
precipitation potential and then somewhat inflated SLR from blends
keeps the forecast totals just below 6" near the Iowa Great Lakes,
Jackson, and Storm Lake.

Will go ahead and issue a large winter weather advisory across the
CWA.  Will break out the eastern zones into a separate section,
which should make it easier to upgrade to a warning if morning data
suggests more snow and less of a mix. The good news is that winds
will be minimal and should`t create much of an added impact to the
roads.  With temperatures behind this system quickly jumping into
the mid and upper 30s, will trim the ending time accordingly from
west to east. This should also allow for a fairly quick recovery
on the roads.

Thursday: High pressure moves through on Thursday, leading to yet
another cool day in the 40s.

Friday-Sunday:  Models still a bit split on the the eventual track
of the large upper low coming out of the Central Rockies late this
week.  GFS is the most northerly solution, only grazing the forecast
area before the system pulls away.  Favor the ECMWF which has
minimal impact to the area.  Temperatures will begin to moderate
upwards as low level temperatures warm and the snowpack melts. In
fact, the snowpack and fairly minimal mixing each day are the only
things preventing us from reaching closer to normal.

Monday-Tuesday:  Things should get back a bit closer to normal in
this period as winds turn southwesterly and our snowpack should be
more minimal.  Extended guidances suggests a frontal boundary moves
through at the very end of the forecast, but confidence on this
system is far too low to make any meaningful changes.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 617 AM CDT Tue Apr 17 2018

VFR conditions through the daytime hours and into the early
overnight hours. Ceilings begin to lower after midnight as
precipitation starts to move eastward. The greatest impact from
precipitation will arrive after midnight for Huron, and after 3am
for Sioux City and Sioux Falls. IFR to LIFR conditions will be
possible by the very end of the TAF period.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 1 AM to 4 PM CDT Wednesday for
     SDZ038-039-053>055-060>062-066-067-070-071.

     Winter Weather Advisory from 1 AM to 1 PM CDT Wednesday for
     SDZ052-057>059-063>065-068-069.

     Winter Weather Advisory from 4 AM to 7 PM CDT Wednesday for
     SDZ040-056.

MN...Winter Weather Advisory from 4 AM to 7 PM CDT Wednesday for
     MNZ071-072-080-081-089-090-097-098.

IA...Winter Weather Advisory from 1 AM to 4 PM CDT Wednesday for
     IAZ001-012-020>022-031-032.

     Winter Weather Advisory from 4 AM to 7 PM CDT Wednesday for
     IAZ002-003-013-014.

NE...Winter Weather Advisory from 1 AM to 4 PM CDT Wednesday for
     NEZ014.

&&

$$

SHORT TERM...Dux
LONG TERM...Dux
AVIATION...Dux



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