Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 181111

Area Forecast Discussion
National Weather Service Sioux Falls SD
511 AM CST Thu Jan 18 2018

.SHORT TERM...(Today and Tonight)
Issued at 405 AM CST Thu Jan 18 2018

A wrapped up short wave and vort max is currently moving
southeastward across the western Great Lakes region, but has no
bearing on our weather other than passing cirrus. At the surface,
similar to yesterday winds will be from the southwest, but perhaps
not quite as brisk. The one exception could be on the downslope
side of the Buffalo Ridge in parts of southwest MN where winds may
be a bit breezy. Otherwise it will be a seasonably pleasant day
with mild highs ranging from the upper 30s in our far eastern
zones, to the upper 40s in our south central SD areas. For lows
tonight, used a combination of guidance readings which picked up
on terrain features, which keeps river valleys much cooler than
exposed terrain.

.LONG TERM...(Friday through Wednesday)
Issued at 405 AM CST Thu Jan 18 2018

Friday continues to look like an exceptionally warm January day,
with zonal flow aloft under a broad ridge of high pressure.
Temperatures will run about 20 degrees above average for this time
of year. Partly sunny skies with light winds will aid in continuing
to melt snow across the region. Saturday will also be warm, 10 to 15
degrees above normal, with increasing cloud cover ahead of the next
weather system.

Saturday night into Sunday morning, a high amplitude upper level
trough moves over the central Plains. Strong dynamic support aloft
will quickly deepen surface low pressure to the south and
southeast of the tri-state area. This track puts the region in the
northwest quadrant of the surface cyclone: a favorable location
for snow production. Uncertainty remains on snow amounts, as some
models, including the ECMWF have a less progressive upper trough,
which causes the surface cyclone to develop a bit further south
and east, therefore reducing snow potential for all except
northwest Iowa. This is in contrast to the 12Z ECMWF which curled
the cyclone to the northeast producing heavy amounts of QPF over
much of our area.

Another threat with this system will be lowered visibility due to
blowing snow. A tight pressure gradient is likely to cause 20 to 30
mph winds that will gust to 30+ mph. Those traveling on Sunday into
Monday may want to leave extra time to get to their destinations,
because any snow that does fall, regardless of amounts, will be on
the move, causing winter driving conditions.

A third potential with this system is a brief period of freezing
drizzle as the system arrives Sunday morning. This would be
primarily limited to northwest Iowa during the Sunday morning
timeframe, and accumulations look very light. If the system is
slower to arrive, this could be a moot point, given colder air would
keep the precipitation type as all snow.

Without getting lost in the details, a few things are becoming
clear: 1) Snow continues to look likely for Sunday into Monday. 2)
Areas of blowing snow are likely, as winds will be strong as the
system moves through. 3) Plan for a return to winter driving
conditions Sunday and Monday.

Winds lighten up Tuesday through Thursday, with quieter weather
expected as a more seasonally cool air mass moves in behind Sunday
and Monday`s system. Ridging aloft looks to keep precipitation
potential low during this period.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 511 AM CST Thu Jan 18 2018

Only high clouds will be found across the area, producing VFR
conditions through tonight.




LONG TERM...VandenBoogart
AVIATION...MJ is the U.S. government's official web portal to all federal, state and local government web resources and services.