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Area forecast discussion
National Weather Service Sioux Falls South Dakota
552 PM CST Thu Dec 12 2019

Short term...(this evening through friday)
issued at 317 PM CST Thu Dec 12 2019

Low stratus clouds at temperatures near -10 c will promote
scattered flurries this afternoon as ice nuclei activate within
the dendritic growth zone. No measurable snowfall is expected, but
a light dusting is possible for some locations. These low clouds
continue overnight, with low temperatures in the low teens to mid
single digits.

A weak shortwave will move through the westerly flow aloft Friday
morning. This wave provides subtle lift as the Sioux Falls region
sits under the deformation zone. For this reason, have kept some
chance pops in the forecast through the afternoon. There is not a
lot of atmospheric moisture available with this wave which keeps
expected precipitation amounts minimal west of I-29. A dusting to
an inch is possible further east in locations such as Windom Minnesota
and Spencer IA, as forcing will increase as the wave traverses
the area. Given temperatures aloft will be warmer than -10 c in
the saturated layer, patchy freezing drizzle could mix with snow,
but snow looks to be the dominant precipitation type, as colder
mid-level clouds provide crystals for Snowflake growth a majority
of the time the lift is present. Afternoon temperatures Friday will
be the warmest of the next 7 days, with highs in the mid 20s to
mid 30s.

Long term...(friday night through thursday)
issued at 317 PM CST Thu Dec 12 2019

A cold front will push through Friday night into Saturday morning,
with wind gusts of 25 to 30 mph. Light snow will again be possible
ahead of this front Friday evening, but cold and dry air will be in
place by Saturday morning, ending chances for light snow. The
Canadian air mass will keep temperatures quite chilly Saturday &
Sunday. Besides a few flurries Sunday afternoon and evening,
precipitation is not expected for the weekend.

Cold, below-average temperatures continue into next week. The large-
scale pattern remains largely unchanged through Wednesday night,
with a longwave trough over Hudson Bay and a ridge over the western
Continental U.S.. this keeps the Sioux Falls area in quiet northwesterly flow,
with the jet stream and active weather well to the south. The ridge
could strengthen and shift eastward Wednesday into Thursday, which
would help bring more mild and seasonable temperatures mid-week,
but confidence in this scenario is currently low, given recent
model runs have tended to overestimate the eastward progression of
these longwaves.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 535 PM CST Thu Dec 12 2019

Stratus deck maintains its hold across the area into Friday, with
MVFR and IFR conditions. Winds remain light and variable. Patchy
fog is possible, especially along the edge of the stratus into
late Friday morning. Patchy fog could drop conditions to LIFR for
a brief time. Some areas could see light snow, mainly along/east
of I-29 through the overnight Thursday into late Friday morning.

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

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