Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 231753 AAB

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
1153 AM CST Fri Feb 23 2018

.SHORT TERM...(Today and tonight)
Issued at 422 AM CST Fri Feb 23 2018

Snow will end across the region today, but low clouds will linger
for most of the day. Winds will become west northwest, but switch to
the northeast ahead of the next storm system that will bring a
narrow swath of heavy snow across Minnesota/Wisconsin.

Early morning satellite imagery together with radar and surface obs
showed snow exiting to the northeast this morning. Surface obs
reports some unknown precip, and forecast soundings show a loss of
ice, but so far no freezing drizzle has been observed at the office
so it must be either very spotty or very light. Regardless,
continued to mention freezing drizzle in the forecast but at this
point it does not appear to be accumulating and should have little if
any impact.

Later today high pressure will build in across the region, but
forecast soundings show low level moisture atop the boundary layer
so may have trouble breaking out of the stratus this morning. If
skies do clear Friday night, temperatures could drop off
significantly with the fresh snow pack and light winds.

.LONG TERM...(Saturday through Thursday)
Issued at 422 AM CST Fri Feb 23 2018

The forecast snow event for Saturday-Sunday remains on track and is
obviously the main concern in the long term period.

The main upper trough is currently positively tilted across the
intermountain west.  Over the next 24 to 36 hours, the northern end
will remain relatively anchored, while the strengthening subtropical
jet to the south aids the main wave in advancing eastward, allowing
the system to gain a negative tilt by midday tomorrow.  Meanwhile,
surface cyclogenesis will occur tomorrow morning and by 18Z tomorrow
the surface low will be in south central Kansas.  The 500H trough
and PV advection is impressive but will move northeast rather
quickly.  By midday tomorrow, the jet pattern is quite favorable for
a deepening cyclone given the offset jet streaks working together in
their left exit and right entrance regions in addition to the
impressive 500H wave pivoting and gaining that negative tilt.  So,
it makes sense to see the models deepen the low by 12mb in a 12 hour
period from 18Z tomorrow through 06Z Sunday as it moves from south
central Kansas to southwestern Wisconsin.

So, the forcing looks good with this system and there will be
plenty of moisture to work with.  The issues to be concerned about
when considering the highest snow amount potential is the fact that
the system is moving rather quickly and the forecast convection
along the cold front south of the surface low.  With the speed of
the system slightly faster, QPF and hence snow amounts were trimmed
slightly from the previous shift, but the placement of the heaviest
snow still looks to be from south central MN through the metro
toward eastern Lake Superior.  Much of this area can expect 6-8" of
snow from this system, with some areas of enhancement picking up 8-
10".  Did increase the wind speed forecast over the blended guidance
with the deepening low moving through eastern Iowa and into
Wisconsin.  The winds don`t look overly strong, with peak speeds
forecast to reach the 25-30 MPH range on the back side of the snow.

Beyond this system, the following several days will be quiet.  No
precipitation and near to slightly above normal temperatures are
expected.  There is more potential acitivity to monitor for the end
of next week though, as the guidance continues to show a mid
latitude cyclone moving through the center of the country.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1153 AM CST Fri Feb 23 2018

The rapid clearing from this morning has stalled across eastern
MN, with stratocu filling in behind the clearing line. Expecting
these to gradually mix out as drier air continues to work in. The
abundance of sun today areas to the west combined with the fresh
snow cover will lead to some melting as temperatures approach
freezing. Temperatures tonight will then plummet into the single
digits above and below zero, well below current dew point values.
This should result in widespread freezing fog tonight, which will
likely be dense in some locations. The fog should improve
Saturday morning, but low clouds may remain. Snow will begin
Saturday afternoon from southwest to northeast and become heavy
rapidly by evening with LIFR conditions expected.

KMSP...The clearing had almost made it, and then the clouds
started filling in again. Still expecting clearing this afternoon
and mostly clear skies tonight. Fog will likely develop overnight,
with visibilities less than a mile. Some improvement Saturday
morning, before a wall of snow arrives mid afternoon. Conditions
are expected to deteriorate rapidly by Saturday evening with 1 to
2 inch per hour rates possible until 06Z Sunday.

Sun...MVFR. Wind W at 20G25kt.
Mon...VFR. Wind SW at 15G20kt.
Tue...MVFR with -sn possible. Wind NE at 05kts.


WI...Winter Storm Watch from Saturday afternoon through late Saturday
     night for WIZ014>016-023>028.

MN...Winter Storm Watch from Saturday afternoon through late Saturday
     night for MNZ043>045-049>053-057>063-066>070-076>078-084-

     Winter Storm Watch from Saturday afternoon through late Saturday
     night for MNZ056-064-065-073>075-082-083-091-092.



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