Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230552 AAC
AFDMPX

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
1152 PM CST Wed Feb 22 2017

.UPDATE...
Issued at 952 PM CST Wed Feb 22 2017

The 00Z guidance is beginning to come in and the NAM remains
the furthest west with the axis of heaviest snowfall amongst the
global models (GFS, ECMWF, Canadian). It has trended southeast
slightly with time, but it has a lot more trending to do before
catching up with the southeasternmost guidance. The 00Z GFS has
trended even further east and now barely scrapes the metro with
measurable snow. Confidence is much lower than 24 hours ago.
Generally, south central Minnesota to west central Wisconsin
remains the best area for heavy accumulations and the big question
is where the back edge of the snow will set up. Right now there
is too little confidence to answer that question and will need to
wait for the rest of the 00Z guidance. Therefore, there are no
plans to adjust the headlines yet, however it is looking increasingly
likely some of the Winter Storm Watch will need to be cancelled.

Did adjust PoPs and snow amounts according to the 00Z model trend.
Further adjustments will be needed overnight.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 317 PM CST Wed Feb 22 2017

The large system that will impact the area tomorrow afternoon
through Friday is just pushing onshore this afternoon, so it still
has quite an amount of ground to cover.  Between now and then, cold
air advection is beginning across western MN as a subtle surface
trough drifts through, turning winds northwesterly which will only
expand across the area tonight and increase in speed across western
MN.

We had a few showers and thunderstorms move east across central MN
and we could continue to see some light rain move through central MN
and parts of west central WI.  QPF will be minor with any precip
that does develop.

With the cooler airmass filtering in from the north, highs tomorrow
will be cooler than recent days.  Highs are expected to be in the
upper 30s to lower 40s.  Surface cyclogenesis overnight across
eastern Colorado will lead to the surface low ejecting northeast
during the day tomorrow.  As this occurs, our winds will turn
northeasterly and slowly increase in the afternoon.  The baroclinic
zone draped across southern MN/northern Iowa will be the focus of
initial precipitation development tomorrow afternoon.  Given
temperatures will be in the upper 30s and low 40s, expect light rain
to start things off in the afternoon, but not taking long as
evaporative cooling and strong dynamics support the switch to snow
by the end of the short term period tomorrow early evening across
southern MN.

.LONG TERM...(Thursday night through Wednesday)
Issued at 317 PM CST Wed Feb 22 2017

Confidence has not increased in the exact location of the heavy snow
band based on the 12Z guidance.  It still could be anywhere along a
line from Canby MN through St Cloud, or else from Rochester MN
through Eau Claire WI. That makes Mankato MN through the Twin Cities
right in the middle, which is what the current forecast depicts.
With that said, there are a few areas where confidence has increased.

The first is the initial east/west warm advection band of snow that
will develop Thursday evening and shift northward overnight. The
strong Fgen driving this precip will lead to heavy snowfall rates of
1 to 2 inches per hour, so over 2 to 3 hours should see a quick 3 to
6 inches of snow just in time for the Friday morning commute. Then
there will likely be a lull across eastern MN and western WI as the
deformation band becomes more active in central MN before shifting
eastward and exiting the region Friday evening.

This deformation band of snow will set up more of a southwest to
northeast orientation and bring several more inches of snow,
especially as the cyclone matures and a TROWAL develops. There is
less confidence in where this band will set up, so that is why there
isn`t confidence to issue a warning. The winds remain strong on the
Bufr soundings, so this increases the threat for widespread whiteout
conditions enough to have a blizzard watch for southwest MN.

As for the models, the 22.12 ECMWF and GEM continue to be the
furthest south, with the highest snow along a line from northern IA
through southeast MN and western WI. This matches up with a local
non-latent heat WRF-run, which doesn`t represent reality since it
doesn`t include the effects of latent heating. Meanwhile, the
parallel, latent heat version has the highest axis of QPF to the
northwest through Mankato and the Twin Cities.  This also lines up
better with the HiRes ARW/NMM, which have the heaviest QPF on the
northern side of the various model solutions. The 22.12 GEFS
probabilities are focused to the south a bit and lines up better
with the WPC official snowfall forecast. Bottom line is that there
is still a fair amount of spread among the model guidance, and
don`t want to discount the northern solutions of the HiRes models.

The totals of 12+ inches remains likely in this heavy snow band.
SREF probabilities have converged on higher values in the axis of
heavy snow. So, for planning purposes, expect to see travel impacts
from this storm, and possibly some road closures. Power outages are
possible as well since the heavy wet snow and strong wind could
cause some branches to fall.

Looking ahead, another storm will emerge from the desert southwest
early next week. This storm continues to get stronger with each
model run, but still remains east of the forecast area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1152 PM CST Wed Feb 22 2017

MVFR cigs are clearing across central MN as drier air rapidly
dives south. Expecting low level clearing at all the TAF sites
late tonight or early Thursday with high clouds remaining. Then,
snow will advance northward Thursday evening, but models have
shifted the heavy snow potential considerably south and it`s
possible RWF, MSP, and RNH will be on the edge of the steady snow.

KMSP...Biggest concern will be timing the MVFR cigs out and the
snow for Thursday night. Current timing appears to be between
10-11Z but it could be earlier if holes begin breaking up the
overcast as is the case near STC. As for the snow, it looks like
MSP is on the northwest fringe of the heavy snow now and it may be
the case most of it remains south.

/OUTLOOK FOR KMSP/
Fri...IFR/-SN likely early. Wind N 20G35kt.
Sat...VFR. Wind NW 10-15 kts.
Sun...VFR. Chc MVFR/-SN. Wind light and variable.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Thursday evening through Friday evening
     for WIZ014>016-023>028.

MN...Blizzard Watch from Thursday evening through Friday evening for
     MNZ065>067-073>076-082>084-091-092.

     Winter Storm Watch from Thursday evening through Friday evening
     for MNZ044-045-049>064-068>070-077-078-085-093.

&&

$$

UPDATE...BORGHOFF
SHORT TERM...SPD/DWE
LONG TERM...JRB
AVIATION...BORGHOFF



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