Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

000
FXUS63 KFSD 142210
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
410 PM CST Sun Jan 14 2018

.SHORT TERM...(This evening through Monday Night)
Issued at 409 PM CST Sun Jan 14 2018

Impressive jet/trop fold diving into north central SD at late
afternoon, as deepening trough settles toward Minnesota.
Concentrated PV advection at the nose continues to drive a solid
area of snowfall across eastern SD/SW MN/northern NW IA, which is
expected to progress rapidly out of the area through northwest Iowa
and northeast Nebraska by very early evening. Additional amounts
from late afternoon and very early evening will vary from up to an
inch in parts of southwest MN toward the Iowa Great Lakes, dropping
off to a trace northwest of a Brookings to Chamberlain line. While
the measurable threat will end quickly, atmosphere behind the arctic
front (along a Marshall-Sioux Falls-Lake Andes line at 21z) starts
to exhibit a weak/shallow instability atop the mixed layer through
the evening hours into the early overnight across parts of southwest
MN and northwest IA. GOES-East composite imagery clearly defining
development of cloud streets back across North Dakota, Given temps
in dendritic zone within cloud layer, would expect at a minimum
scattered flurries, perhaps a brief snow shower.

Outside the snowy challenges, the main impact of the passage of the
arctic front will be the chill which will dominate the area over the
next few days.  Temperatures will begin to fall tonight, more
sharply after midnight, with winds increasing as a result of a
strong northwest gradient and alignment of increasing isallobaric
support (difference of up to 8 Hpa/3h between max/min). Winds are
likely to gust to 30 to 40 mph for a time ahead of pressure rise
maximum this evening, then settle back a bit later in the night.
There is 30 to 35 knots of wind atop the mixed layer right through
the day on Monday, with continued cold advection, suggesting that
winds gusts will refresh during the day. Temps will also continue to
fall well into the morning on Monday, meaning some of the coldest
wind chills will be on Monday morning.  By Monday night, will begin
to see a more appreciable drop in winds, somewhat less ahead of the
ridge across southwest MN, but also colder temperatures which will
repeat the more extreme bitter wind chills again Monday night into
Tuesday morning. Wind chill warnings will be expanded into later
tonight and Monday across east central SD and southwest MN toward
Iowa Great Lakes with wind chill values expected to drop to -35 to -
40 by Monday morning, and only limited recovery through the day.
Other areas will remain in a wind chill advisory tonight through
Tuesday.  The winds will also create some patchy to areas of blowing
snow starting this evening, and continuing until it is expected to
become more compacted around midday Monday.

.LONG TERM...(Tuesday through Sunday)
Issued at 409 PM CST Sun Jan 14 2018

Winds will eventually drop off more considerably as surface ridge
builds across the area on Tuesday.  Tuesday night, there should be a
precipitous drop in temps during the evening near the ridge axis
which will be close to I-29 or just east early in the evening, but
overall an increasing southwesterly flow and strong warm advection
later Tuesday night will likely bring rising overnight temps.

Warmer conditions will dominate the end of the week as a broad ridge
at larger scales expands through the plains. 12Z GFS suggested a
moisture starved but sharp trough moving across SD Wednesday night,
but EC much further north.  Latest models trending north, so should
do no more than intensify the warming, with 20s to lower 30s
Wednesday giving way to 30s and lower 40s Thursday, and upper 30s to
mid 40s on Friday.

To associate uncertainty with the pattern by the weekend would be an
understatement. There is some agreement that a split flow system
will traverse western North America and emerge in the plains by
later Saturday to Sunday. Variation in solutions is immense over
collective of models and recent runs, so best to keep things at a
chance level for the time. May be warm enough for a little rain over
northwest IA and adjacent areas on the leading side of the system.
Temps back to near/just below normal around Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1142 AM CST Sun Jan 14 2018

Primary concern for aviation is the snow and clouds expected
through early tonight. An area of snow is expected to move
southward reaching KHON around 18Z, KFSD at 20Z and KSUX at 22Z.
In all 3 locations visibilities of 1-3 miles is expected. At KFSD
and KSUX it is not out of the question there could be a brief -
less than one hour - period of less than 1 mile visibility but the
probability is less than 50% with the better chance farther east
in southwestern Minnesota. Any snow is expected to last 2 to 4
hours. This snow will be preceded by IFR ceilings at KFSD and
KSUX. As the winds switch to west and snow moves in, ceilings are
expected to improve above 1000 ft. Once the snow exits, strong
subsidence and winds behind the arctic front should initially
erode the clouds leaving VFR conditions. However, winds will be
gusts to near 30 kts from early tonight through Monday morning.
Did keep VFR conditions into Monday morning although increased
cyclonic flow and low level moisture do increase the threat of
1000 to 3000 ft ceilings with stratocumulus. At this time, kept
skies scattered but will need to be monitored with future
forecasts.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Chill Advisory from 3 AM Monday to noon CST Tuesday for
     SDZ038-050-052>054-057>061-063>071.

     Wind Chill Warning from midnight tonight to noon CST Tuesday for
     SDZ039-040-056.

     Wind Chill Warning from 6 PM Monday to noon CST Tuesday for
     SDZ055-062.

     Wind Chill Advisory from 3 AM to 6 PM CST Monday for SDZ055-062.

MN...Wind Chill Warning from midnight tonight to noon CST Tuesday for
     MNZ071-072-080-081-089-090-097.

     Wind Chill Warning from 6 PM Monday to noon CST Tuesday for
     MNZ098.

     Wind Chill Advisory from 3 AM to 6 PM CST Monday for MNZ098.

IA...Wind Chill Advisory from 3 AM Monday to noon CST Tuesday for
     IAZ012-013-020-021-031-032.

     Wind Chill Warning from midnight tonight to noon CST Tuesday for
     IAZ003.

     Wind Chill Warning from 3 AM Monday to noon CST Tuesday for
     IAZ014-022.

     Wind Chill Warning from 6 PM Monday to noon CST Tuesday for
     IAZ001-002.

     Wind Chill Advisory from 3 AM to 6 PM CST Monday for IAZ001-002.

NE...Wind Chill Advisory from 3 AM Monday to noon CST Tuesday for
     NEZ013-014.

&&

$$

SHORT TERM...Chapman
LONG TERM...Chapman
AVIATION...Schumacher



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.