Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 241125
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
525 AM CST Tue Jan 24 2017

.UPDATE...
Issued at 525 AM CST Tue Jan 24 2017

Updated to include 12Z aviation discussion below.

&&

.SHORT TERM...(Today and tonight)
Issued at 250 AM CST Tue Jan 24 2017

Primary forecast concern for today and tonight is obviously the
storm system that will be working its way northeast from the
southern Plains into our area. The 00Z guidance has nearly all
slowed things down and shifted a bit south in terms of the track of
the surface low and area of heaviest precipitation. This still
brings the greatest snow potential to the I-90 corridor and
southward. A few solutions, particularly within the SREF membership,
are notably farther north, but appear to be outliers. A consensus of
the NAM, GFS, and ECMWF looks to be a reasonable overall forecast,
with some of the details from CAM guidance helping to fine tune
precipitation amounts and gradients.

Should see snowfall work into from the southwest by late afternoon,
then lift north through the evening hours before starting to pivot a
bit to the northeast overnight. The 290K isentropic surface looks to
capture the overall area of snow fairly well in terms of where its
positive pressure advection and lower condensation pressure deficits
match up. Although it does envelop a good portion of the area by mid
to late evening, the strongest ascent is indicated across the
southern portion of the area, matching up with with the model
precipitation output. Frontogenesis, in both 850-700 mb and 700-500
mb layers, is also most pronounced over the far southern portion of
the area tonight, helping to increase confidence in the placement of
highest accumulations in that area. In addition, local WRF ARW
latent/no-latent heat sensitivity runs show very minimal differences
in their solutions, which is quite remarkable, and helps to further
increase confidence that the operational guidance has likely
narrowed in on a solution that should be close to reality. The GEFS
has been remarkably consistent for the past few days, and its
probabilities of precipitation > 0.50" (and snowfall > 6") continues
to highlight the southern portion of the area, with the northern
edge of the probability gradients getting into the southern metro.

So, the existing warning area still looks on track, except for
perhaps Redwood county, while the watch area should see advisory
amounts. Luckily, it appears the main snow window in the metro will
be well after the evening commute, which will help to mitigate
impacts to some extent. Advisory amounts to appear to sneak a bit
farther north across the Wisconsin counties, so some expansion in
that area looks necessary. Winds do not look to be overly strong
with the system, with the strongest winds out west. Amounts in that
area look to be marginal for an advisory, but with some higher wind
gusts expected, there could be some blowing snow impacts so
transitioning from a watch to an advisory there seems appropriate.

.LONG TERM...(Wednesday through Monday)
Issued at 250 AM CST Tue Jan 24 2017

Resolution of the snow event remains the main forecast issue in the
Wednesday time frame. Following the storm...the flow pattern
becomes northwest aloft bringing in a cooling trend.

The storm system should travel from eastern Iowa 12z Wed to southern
Lake Michigan by late Wednesday afternoon. Snow should continue over
the southern portion of the area through the morning and begin to
trail off into the afternoon as the upper low/deformation band exits
to the east. We are seeing an additional 1 to 2 inches in this
region into the afternoon. As the deep/occluded system moves
east...northwest winds are expected to increase during the day
Wednesday.  This may held reduce visibility especially with falling
snow. It will be a heavier/wet type snow...so significant
blowing/drifting should be limited. We will continue to mention at
least some patchy blowing snow southwest/south central during the
day.

The remainder of the period should remain on the mostly cloudy and
colder trend. Not unusually cold and probably remaining slightly
above normal much of the period.  Deterministic models suggest a
couple of short wave troughs/surface fronts dropping southeast over
the area. The first in the Saturday time frame...which could bring a
few snow showers/flurries to the region. The other in the
Monday/Tuesday time frame. We could see some brief warming ahead of
the front if the track of the surface low remains farther north.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 525 AM CST Tue Jan 24 2017

MVFR ceilings look to perist today, with some spotty MVFR
visibilities across the eastern part of the area. However, the
main weather issue will be the storm system that will move
northeast toward the area tonight into Wednesday. Snow is expected
to overspread most of the area from late afternoon through the
evening, with the most significant snow south of all TAF sites.
However, most locations should eventually see visibilities drop in
some snowfall, along with a lowering of ceilings. Improvement in
conditions doesn`t look to occur until after this forecast period.

KMSP...Primary uncertainty is the timing of snow arrival tonight,
and the degree to which visibilities and ceilings will be
impacted. For now, stuck close to the model consensus, but later
updates should be able to narrow things down better as snow starts
to approach the forecast area.

/OUTLOOK FOR KMSP/
Wednesday afternoon...MVFR expected with a chance of snow. North
wind 10 to 20 kt.
Wednesday night...MVFR expected with a slight chance of snow.
Northwest wind 10 to 20 kt.
Thursday through Friday...MVFR possible with a slight chance of
snow. Northwest wind 10 to 20 kt.
Friday night...MVFR possible early. Northwest wind around 10 kt.
Saturday...MVFR possible with a chance of snow. Northwest wind 5
to 10 kt.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Wednesday for WIZ024>028.

MN...Winter Weather Advisory from 6 PM this evening to noon CST
     Wednesday for MNZ064-065-067-069-070-073.

     Winter Storm Warning from 3 PM this afternoon to 6 PM CST
     Wednesday for MNZ074-082>085-091>093.

     Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Wednesday for MNZ075>078.

&&

$$

UPDATE...
SHORT TERM...
LONG TERM...DWE
AVIATION...



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