Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 241807

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1207 PM CST Sat Feb 24 2018

Issued at 1133 AM CST Sat Feb 24 2018

Heavy snow has reached southwest Minnesota late this morning and
will continue to build northeast through the afternoon. Timing
appears to be an hour or so quicker than last forecast, both
beginning and ending. The biggest update was to increase QPF and
snowfall totals across western MN where a meso low in the
northwest portion of the inverted trough may enhance snowfall a
bit more. QPF is still heaviest across eastern MN into northwest
WI, but snow ratios will be lower there than out west. Therefore,
expecting a fairly uniform 5 to 8 inches across just about the
entire CWA, with the heaviest likely falling across east central
MN into northwest WI. With snowfall amounts around 6 inches across
west central MN, thought about upgrading to a warning but it
seems a bit too marginal and winds will remain light. If impacts
become worse than currently expected, an upgrade can be made this
afternoon. The heaviest rates will likely remain in the current
warning area, and cannot rule out thundersnow there either.


.SHORT TERM...(Today and tonight)
Issued at 422 AM CST Sat Feb 24 2018

Early morning water vapor imagery reveals the upper trough is moving
east over the four corners region as of 09Z.  The latest surface
analysis indicates surface cyclogenesis occurring near the
Colorado/New Mexico border.  Closer to home, we`re still under high
pressure early this morning with much of the area under a dense fog
advisory through 15Z.  We do recommend you exercise caution on the
roadways this morning, as fog at these cold temperatures may produce
slick conditions on area roads.

The forecast for the snow later today remains largely on track.  The
most notable change was to drop the snow amounts down around an
inch or so, mainly due to the relatively high speed of the system,
which limits the amount of time spent under moderate/heavy snow. The
placement of the heavies snow, which should be about 5-7", remains
in the Winter Storm Warning area.  Did not need to make any
adjustments to the warning or advisory issued yesterday.  There is
still some uncertainty with this event.  The QPF from the various
guidance does vary, so continued to stick with a blended approach.

The impressive shortwave will gain a negative tilt as it races
northeast toward our area later today.  Impressive forcing is
expected and there even looks to be some elevated instability with
the snow this afternoon and tonight.  Most of the accumulation will
come in a 4-6 hour period of moderate to heavy snow, with the timing
dependent on your exact location.  For the Twin Cities, the heaviest
snow will move through from about 3PM-9PM. Travel will quickly
become difficult as the snow spreads in from the southwest this
afternoon, as visibilities will crash very rapidly at the onset.  On
top of that, 1-2"/hr rates are likely, so the snow will pile up
quickly on the roads.  Alter travel plans if possible.

The snow will come to an abrupt end late tonight from southwest to
northeast.  The wind speeds will then increase overnight, especially
across far southern MN.  Winds of up to 30 MPH will lead to some
blowing and drifting snow overnight, hence travel will remain
difficult overnight.

.LONG TERM...(Sunday through Friday)
Issued at 422 AM CST Sat Feb 24 2018

Quiet weather expected for next week with temperatures near or
slightly above the seasonal average for late February. The storm
track will generally be to the south, so little if any precipitation
is expected.

There is a slight chance for a strong storm to develop and move
across the region Wednesday into Thursday, but this storm is
trending a bit further south. The origins of this storm are from a
positively tilted upper level trough off the coast of California,
and these systems generally are poorly handled by the numerical
models. The 24.00Z ECMWF is farther south than the GFS and GEM.
Given the uncertainty in both the large scale pattern, and the
spread in the forecast models, at this time feel there is a better
chance of it not happening than of it happening. In other words,
something to watch, but not something to hang your hat on since it
will likely end up south of the forecast area.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1206 PM CST Sat Feb 24 2018

An Airport Weather Warning is in effect until from 3-11 PM for
heavy snow. Visibilities are expected to become LIFR by 21Z and
remain below 1SM until the snow ends around 11PM. The heaviest
snow is expected between 5-8PM when visibilities may drop as low
as 1/4 mile at times. Expect snowfall rates of 1-2" per hour
during the event & a storm total snowfall of 6-8".




WI...Winter Storm Warning until 6 AM CST Sunday for WIZ023-024-026.

     Winter Storm Warning from 6 PM this evening to 6 AM CST Sunday
     for WIZ014>016-025-027.

     Winter Weather Advisory from 6 PM this evening to 6 AM CST
     Sunday for WIZ028.

MN...Winter Storm Warning until 6 AM CST Sunday for MNZ050-051-

     Winter Weather Advisory until 6 AM CST Sunday for MNZ041>043-048-

     Winter Storm Warning from 6 PM this evening to 6 AM CST Sunday
     for MNZ044-045-052-053.

     Winter Weather Advisory until 3 AM CST Sunday for MNZ047-054>056-

     Winter Storm Warning until 3 AM CST Sunday for MNZ065-073>075-



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