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fxus63 kfsd 211137 

Area forecast discussion
National Weather Service Sioux Falls South Dakota
537 am CST sun Jan 21 2018

Short term...(today and tonight)
issued at 334 am CST sun Jan 21 2018

Amplified trough with base over Desert Southwest is evident on water
vapor imagery. Lee cyclogenesis will commence as the main vort
lobe rotates through the trough and a closed 500 mb low ejects
into the Texas/OK Panhandle/SW Kansas through the morning/early afternoon
hours. Meanwhile, mid level frontogenesis has led to a band of
light radar returns across our far northern coverage area early
this morning, although dry air is largely limiting anything
reaching the ground at this point. This should begin to change
through the morning as a band of snow develops across our
northwestern counties from around Chamberlain to De Smet.
Additionally, as moisture continues to saturate the lower levels
below the ice growth zone, expect drizzle or freezing drizzle to
become possible across our northwest Iowa counties.

Upper level wave continues to lift northeast with the surface low
moving into NE Kansas by late evening/overnight and southeast Iowa by Monday
afternoon. Aloft, a jet streak will extend from Texas to Iowa/Illinois with our
region benefiting from the added lift from this favorable jet
dynamic. This is also noted in solid div q, most focused over our
southeast half counties. Also expect to see some convective
enhancement over the previously mentioned southeast half of our forecast area
with models advertising favorable lapse rates, occasional negative
epv* above the frontogenetic forcing and even some elevated cape
being flagged. Forecast soundings are also rather impressive at
times with Omega in the dendritic growth zone. Finally, the best
trowal signature rests over this area, further enhancing confidence
of enhanced snowfall rates in this region. Would note be surprised
to see some thundersnow which further complicates snow amounts
with its inherent localized nature. It is also Worth noting that
this corridor south of Sioux Falls to near Sioux City is also
painted in the gefs extreme forecast index (efi) for
precipitation. Will still need to watch for a period of icing
across our far southeastern counties near Storm Lake/Ida Grove as
the dry slot swings near. As of now, any icing amounts look
fairly light.

Winds will also be a big concern with this tightly wound system.
Good pressure packing will be focused across southeast SD, SW Minnesota and northwest Iowa
with 925 mb winds in the 35-45 kt range. This should translate to
surface winds of 20 to 30 mph with gusts up near 35-40 mph at times.
This will no doubt cause issues with blowing and drifting snow and
reduced visibility.

Impacts: this will clearly be an impactful winter storm for the
region. With the help of some convective enhancement, expect to
see some snowfall amounts near or over a foot from south of Sioux
Falls to near or just north of Sioux City. With this in mind, a
very sharp gradient in snow amounts is also expected on either
side of this heavier band. The likelihood of snow totals varying
greatly over small distances can not be emphasized enough and any
further wobbles in the storm track could lead to further changes.
This uncertainty is further shown in a very wide spread in the
ensemble quantitative precipitation forecast and snow totals. Strong northerly winds will lead to
significant blowing and drifting with blizzard or near blizzard
conditions at times from this evening into Monday. Travel will be
dangerous and not recommended for many areas. Because of the
expected heavy snowfall rates at times, combined with the wind,
have issued a Blizzard Warning for far southeast SD, northwest Iowa
and portions of southwest Minnesota. Winter storm warnings and advisories
buffer this region where either lower snow totals are expected or
somewhat lighter winds.

Long term...(monday through saturday)
issued at 334 am CST sun Jan 21 2018

No changes were made to the extended forecast with relatively quiet
weather expected through the rest of the work week. High
temperatures will gradually warm through the week although will be
impacted by any snow cover that occurs. Light precipitation is
possible by next weekend.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 526 am CST sun Jan 21 2018

Very complex and messy aviation period expected with the approach
of an incoming winter storm. Light rain and snow will begin to
impact khon this morning while some drizzle will become possible
at ksux by late morning in to the afternoon. This will lead to
MVFR to IFR ceilings and/or visibilities at these locations. By
this evening, precipitation will become more widespread with snow
likely at kfsd and a rain/snow mix changing to snow at ksux. This
will result in widespread MVFR to IFR conditions with khon likely
the least impacted. Gusty northerly winds to 30kt will result in
blowing snow and greatly reduced visibilities through the
overnight hours, into the LIFR category at times. Blizzard
conditions are possible across far southeast South Dakota,
portions of southwest Minnesota and northwest Iowa, including
ksux. Near blizzard conditions are possible at kfsd during the
overnight hours into Monday.


Fsd watches/warnings/advisories...
South Dakota...Winter Storm Warning from 6 PM this evening to 6 PM CST Monday
for sdz061-062-065-066-068.

Blizzard Warning from 9 PM this evening to midnight CST Monday
night for sdz067-069>071.

Winter Storm Warning until noon CST Monday for sdz050-063-064.

Winter Weather Advisory from 6 PM this evening to 6 PM CST
Monday for sdz040-054>056-060.

Winter Weather Advisory until 6 am CST Monday for sdz052-053-

Minnesota...Blizzard Warning from 9 PM this evening to midnight CST Monday
night for mnz081-089-090.

Winter Weather Advisory from 6 PM this evening to 6 PM CST
Monday for mnz071-072.

Winter Storm Warning from 6 PM this evening to midnight CST
Monday night for mnz080-097-098.

Iowa...Blizzard Warning from 9 PM this evening to midnight CST Monday
night for iaz001>003-012>014-020>022-031-032.

NE...Blizzard Warning from 9 PM this evening to midnight CST Monday
night for nez013-014.


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