Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 092351

Area Forecast Discussion
National Weather Service Sioux Falls SD
651 PM CDT Mon Oct 9 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 330 PM CDT Mon Oct 9 2017

A band of light rain focused around 700mb was across eastern SD into
southwest MN at 2 pm will continue to gradually shrink and dissipate
as the support from the right entrance region of the upper level jet
shifts southeast. Because levels below about 750mb are dry and
capped off development has not shifted south and as colder and drier
air aloft has entrained into the back edge of the rainfall band, we
have wet bulbed the freezing level down to about 1-2 kft AGL. This
has allowed a little snow to fall on the back edge of the heavier
band. The enhancement with the right entrance region of the upper
level jet appears to shift south of this boundary by late afternoon.
As this happens sometime this evening additional development should
occur a little lower in the atmosphere, likely around 800-750mb, and
another band will develop across parts of northeast Nebraska into
northwest IA. This is in response to the energy across the Rockies
drifting onto the Plains. This should enhance the warm air advection
and bring a more widespread area of rainfall late tonight into
Tuesday morning, with the main effects south of the area. There
should be some measurable rainfall around the Sioux City and Storm
lake areas during the day, but dry air to the northwest will keep
the precipitation at bay.

As this system strengthens to the southwest dry and cold air will
fill in behind. The freeze warning and frost advisory will remain
place because of the decreasing clouds and winds. Lows tonight will
range from the upper 30s near KSUX and KSLB to the mid 20s from K9V9
to KHON. Highs on Tuesday will again be cool and in the 50s. Could
see some upper 40s under the rainfall in northwest IA.

.LONG TERM...(Tuesday night through Monday)
Issued at 330 PM CDT Mon Oct 9 2017

On Tuesday night any left over showers over northwestern IA will end
early, but clouds will linger east of Interstate 29 through the
night. This will hold temperatures up somewhat over that area, with
lows in the upper 30s. Back to the west, clear skies will dominate,
with lows lower to mid 30s.

A southerly flow returns to the region on Wednesday as surface high
pressure slides off to the east. This will result in warming
temperatures, with highs upper 50s to lower 60s. It will be a breezy
afternoon west of I-29 in a tightening gradient with deepening low
pressure over the Northern Rockies/Highs Plains. Thursday will be
even warmer with the approach of the surface trough from the west,
with highs upper 60s to lower 70s.

A cold front slides across the area on Thursday night, and this will
lead to a slightly cooler day on Friday with highs in the lower to
mid 60s. Cannot rule out a few showers on Friday, though the GFS and
ECMWF are differing in their solutions, so confidence is low.

Model differences grow for the upcoming weekend with regard to the
evolution of an upper level trough coming out of the western CONUS.
The GFS is faster in bringing the upper level energy, as well as the
mid/lower level forcing into the Northern Plains on Saturday than
the ECMWF, so the timing in precipitation chances are offset by
about 12 hours. In any event, consensus would suggest drying out by
at least the latter half of Sunday into Monday. Temperatures will be
at or just above normal through the period.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 650 PM CDT Mon Oct 9 2017

Band of precipitation will affect southeast portions of the
forecast area, generally south of Vermillion SD to Jackson MN,
into Tuesday morning. While surface temperatures will result in
primarily rain, cool temperatures within a slightly unstable layer
aloft, above a layer of dry lower level air, is resulting in a mix
with sleet/snow at times. This will be possible through 02Z-03Z,
after which time lower levels begin to moisten, which minimize
potential for frozen precipitation. This could impact KSUX, but
duration should be brief, and thus have not included mention of
sleet or thunder in the KSUX TAF at this time.

Areas north of the precipitation band should remain VFR with light
winds through the period.


SD...Frost Advisory from midnight tonight to 9 AM CDT Tuesday for

     Freeze Warning from midnight tonight to 9 AM CDT Tuesday for

MN...Frost Advisory from midnight tonight to 9 AM CDT Tuesday for

     Freeze Warning from midnight tonight to 9 AM CDT Tuesday for

IA...Frost Advisory from midnight tonight to 9 AM CDT Tuesday for

     Freeze Warning from midnight tonight to 9 AM CDT Tuesday for



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