Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201813

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1213 PM CST Sat Jan 20 2018

.SHORT TERM...(Today and tonight)
Issued at 421 AM CST Sat Jan 20 2018

The short term period will start out quiet, but a warm advection
band of snow could setup across central MN by later tonight in
advance of the winter storm set to impact the region tomorrow night
through Monday night.

The upper level trough that will eventually generate a surface
cyclone to the east of the Rockies is currently just reaching the
coast of California as of early this morning.  For today, another
warm day will continue melting the snow currently on the ground
while we stay south of the upper level jet.  Daytime highs should
have no trouble reaching the upper 30s to lower 40s.  Meanwhile, the
upper trough will continue its eastward progression through the day.
By 12Z tomorrow morning, a deepening closed 500mb low will be
located over the four corners region.

There is a chance we could see a band of light snow develop this
evening across central MN into northwestern WI as a west-east
oriented band of f-gen begins to saturate the column.  If snow does
develop, expect minimal accumulation of less than half an inch.

.LONG TERM...(Sunday through Friday)
Issued at 421 AM CST Sat Jan 20 2018

The winter storm potential for Sunday night-Monday night remains on
track.  Did not make significant changes to the going forecast.  We
still expect a swath of 6-10" of snow with localized amounts
reaching 12" in the heart of the winter storm watch area. Confidence
continues to increase that the placement of the heaviest snow will
be from the southwest corner of the state, through the Mankato area
and toward the Menomonie, WI area.  This track keeps the heaviest
totals just south/east of the Twin Cities.

The main update from the latest guidance is that we have a
convergent trend among the 00Z solutions.  The GFS has held pretty
consistently north of the ECMWF solution, and the 00Z ECMWF shifted
the system a little bit northward from it`s previous solution.  The
NAM continues to be rather inconsistent from run to run, so do not
have much trust in its solution at this time.  The CMC agreed fairly
well with a blend of the EC and GFS.  Looking at the GEFS 21-member
ensemble, it shows really good agreement with the operational ECMWF
forecast and the CMC as well (the operational GFS is on the
northern side of the GEFS ensemble). This increases our confidence
that the heart of the winter storm watch area has the best chance
of getting 6-10" totals. Elected to continue the watch as the
main event really won`t get underway until tomorrow evening in
western MN, and not until after midnight Sunday night in eastern
MN and western WI.

The actual QPF output from the guidance is impressive, with much of
the precip falling during the day Monday.  The NAM and the CMC have
close 1.75"-2.2" of QPF with this system, while the EC, GFS, and
GEFS show a more reasonable 1.0"-1.3" storm total QPF.  We went on
the conservative side with storm total snow given the system is just
now reaching the California coast and there is still
uncertainty/differences in the solutions.

In terms of precip type, the only p-type concern for our area at
this time is along the Iowa border and over toward Eau Claire, where
a period of freezing rain is possible.  Icing amounts still look to
be rather minor and snow still looks to be the primary p-type.  If
the southern track of the ECMWF works out, this would likely keep p-
type issues to our south.  The GFS on the other hand wraps warmer
air farther north.  For now, continued a blended approach of the
guidance for p-type.

Winds still look to increase to the 25-35 MPH range during the snow
Monday which will undoubtedly lead to difficult and dangerous travel
conditions within the heavy snow band.  Whiteout conditions at times
will be possible in open areas, mainly across the western and far
southern portion of MN.

Dry for the remainder of next week, temperatures will run near
normal through midweek, before warming returns late next week.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1212 PM CST Sat Jan 20 2018

Things will break one of two ways this period and it`s all
dependent on the mid/upper clouds we have right now. Route 1 is we
maintain a bkn-ovc mid/upper cloud deck through the night, with
little change in weather conditions over the next 24 hours. Route
2 is we clear out at least some this cloud cover, which would
result in very dense fog forming. Satellite shows plenty of
moisture streaming northeast ahead of the western trough, so
played route 1 in these TAFs for now. Looks like best potential
for clearing is down along the I-90 corridor and depending on how
far north it ends up, could bet MKT, EAU, and maybe MSP into the
dense fog game tonight.

KMSP...If it weren`t for the expected cloud cover, this looks like
one of the rare setups where MSP is in line for dense fog. So as
you can imagine, we will have to watch cloud trends closely.
Otherwise no weather issues until Monday, when MSP will see high
impacts from heavy snow late morning into the evening.

MON...IFR/LIFR +SN/BLSN. Several inches of snow likely. Winds N
      15-25 kts gusting to 30 kts.
TUE...Mainly VFR. Winds NW 5-10 kts.
WED...MVFR chc IFR cigs. Winds 5 kts or less.


WI...Winter Storm Watch from late Sunday night through Monday evening
     for WIZ014>016-023>028.

MN...Winter Storm Watch from late Sunday night through Monday evening
     for MNZ053-059>063-066-068>070-077-078.

     Winter Storm Watch from Sunday evening through Monday evening
     for MNZ064-065-067-073>076-082>085-091>093.



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