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000
FXUS63 KFSD 211809
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1209 PM CST Mon Jan 21 2019

.SHORT TERM...(Today Through Tuesday)
Issued at 308 AM CST Mon Jan 21 2019

Early this morning, we`re continuing to watch a narrow burst of warm
advection snows move northeast across the CWA.  Periods of 1-3 mile
snows have been reported with this band, and it will likely bring
anywhere from a dusting to 1.5" of snow to portions of the CWA.
Highest snow totals may be found along the Highway 14 corridor.

Otherwise, biggest concern in the short term portions of the
forecast focuses on precipitation chances later today through
Tuesday.  Model guidance still not in great agreement with the
passage of a shortwave trough through the Plains tonight and
Tuesday.  GFS/EC/CMC all much stronger with the mid-level wave
moving across Nebraska and into Iowa Tuesday morning. NAM is a bit
of an outlier with this upcoming system, but does suggest a few
areas worth monitoring.

As weak low level warm advection spreads northward later this
afternoon and evening, we`ll begin to see the development of very
light snow or freezing drizzle ahead of an inverted trough
stretching northward across central Nebraska and east central South
Dakota. Soundings suggest the greatest risk for impactful freezing
drizzle may form along the Missouri River, with probabilities
trending lower towards I-90 and then Highway 14.

To the West, a mid-level band of frontogenesis will aid in
developing a linear band of snow across northwest and central
South Dakota after midnight. This band of snow will slowly creep
eastward, arriving in our western zones by daybreak. Where
uncertainty builds in the forecast is with the progression of
potential intensification of a mid-level vorticity maximum
ejecting out of eastern Colorado prior to daybreak Tuesday.
EC/GFS/CMC all indicating this wave deepens sufficiently to
enhance lift and produce a new area of frontal banding in areas
from Yankton to Sioux City and Spencer Tuesday morning, with the
western band quickly decaying after daybreak.  This area of snow
would then traverse across the southeastern third of the CWA
through the afternoon hours.

Accumulation Potential: While there may be a broad area of light
snow across the entire region (Dusting - 2"), feel there could be
two distinct areas of slightly more enhanced snowfalls.  First area
associated with initial banding through central SD and into the
western third of the CWA, and a second enhanced area associated with
the secondary frontogenesis across NW Iowa and NE Nebraska. Snow
amounts in these enhanced areas could approach 2-5".   As far as
icing is concerned, most areas should remain with a glaze.  An area
to watch would be from Sioux City to Storm Lake and Spencer where
there could be some potential of a change from freezing drizzle
to convective freezing rain.

Hazards:  A difficult approach to headlines, given most areas will
see light snows, but remaining under advisory criteria.  At this
point, feel most confident issuing an advisory based on the
combination of freezing drizzle and light snow potential, segmenting
areas of NW Iowa where totals could be slightly higher if
enhanced banding takes place Tuesday. That said, travel even
outside any advisory may be impacted for an extended period given
the prolonged nature of the light snow.

.LONG TERM...(Tuesday Night through Sunday)
Issued at 308 AM CST Mon Jan 21 2019

Tuesday night:  Temperatures should fall quickly Tuesday night, as
light winds and surface ridging move through.

Wednesday: Warm advection and a west to southwest surface wind will
allow temperatures to warm into the 20s again on Wednesday.  We
should see an increase in cloud cover as well.

Wednesday Night and Thursday:  A period of concern for the middle of
the week, as models are all indicating an arctic front will blast
through the region by daybreak Thursday.  A burst of light to
moderate snow will accompany this front, and could produce a quick 1-
2" of snow. The biggest concern though will be with winds.  Behind
the arctic front, soundings indicate nearly 40  knots of flow at the
top of the mixed layer Thursday morning.  Given the very fluffy snow
over much of the area, significant blowing and drifting of the snow
could take place through day.  In open areas, visibility could be
significantly impaired.

Friday-Sunday:  As a large upper trough becomes established over the
eastern half of the CONUS, the CWA will be stuck in the more active
sector of the trough, dealing with systems moving through the
northwest flow nearly every other day.   These system will also
bring a parade of cold fronts across the region through next
weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1150 AM CST Mon Jan 21 2019

Gusty winds from 25 to 35 mph will continue to impact the region
through late this afternoon. This will lead to patchy blowing
snow and MVFR/IFR visibility conditions at times, mainly at KHON
and KFSD.

KSUX: The main concern is -FZDZ this evening into the overnight
hours. Precipitation is expected to change all to snow by early
Tuesday morning.

KHON and KFSD: MVFR to IFR conditions are likely as light
snow moves over the area. Patchy freezing drizzle cannot be ruled
out at KFSD during the evening hours.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Tuesday for SDZ050-063>071.

MN...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Tuesday for MNZ081-089-090.

IA...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Tuesday for IAZ001-002-012.

     Winter Weather Advisory from 6 PM this evening to midnight CST
     Tuesday night for IAZ003-013-014-020>022-031-032.

NE...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Tuesday for NEZ013.

     Winter Weather Advisory from 6 PM this evening to midnight CST
     Tuesday night for NEZ014.

&&

$$

SHORT TERM...Dux
LONG TERM...Dux
AVIATION...05