Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221132

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
532 AM CST Wed Feb 22 2017

.SHORT TERM...(Today and tonight)
Issued at 355 AM CST Wed Feb 22 2017

Still quite mild early this morning ahead of a weak front across
central Minnesota. A few rumbles of thunder/isolated showers also
occurred in west central and south central Minnesota where ample
boundary layer moisture and weak instability existed. Out in front
of this area of showers, weak mixing, and where boundary layer
moisture remained very moist, dense fog formed. Once the showers
occurred, and denser cloud cover moved across the area, visibility
improved. Although localized dense fog will likely continue out
ahead of the showers this morning in west central Wisconsin, I
don`t expect it to continue through late morning.

Only change in today`s forecast was to increase chances of showers
in east central Minnesota, and west central Wisconsin where current
radar and weak instability out of ahead of it, remained. Both the
RAP/HRRR indicated weak instability continuing along this weak front
this afternoon which may generate a few more showers and isolated
thunderstorms. However, I don`t expect much in the way of widespread
coverage, more isolated. Before the front arrives, temperatures will
likely rise into the mid to upper 50s, with a few 60s along the
Minnesota/Iowa border. Current record highs at Minneapolis, and Eau
Claire are in jeopardy. Behind this front, low clouds and fog will
form, which will slide southward overnight.

.LONG TERM...(Thursday through Tuesday)
Issued at 355 AM CST Wed Feb 22 2017

Well, the extended finally no longer includes any periods where we
could see near record high temperatures, but a major winter storm
is still there for Friday.

The system for Friday is coming on shore of northern California
this morning. It is still forecast to take on a negative tilt as
it emerges out of CO/WY Thursday and tracks into the Great Lakes
by Saturday. We continue to have high confidence in significant
snowfall accumulations occurring with this storm with a swath of
12+", but it is a question of where. The NAM sets the bar to the
northwest, the ECMWF/Canadian/MPAS continue to highlight more
northern IA into southeast MN, while the SREF/GFS split the
difference, placing the heaviest snow band right across the Twin
Cities. Looking at postage stamps of total QPFs from GEFS members,
the real outlier among the deterministic models is the NAM. Only
one member of the GEFS gets out to where the NAM is, with the rest
of the GEFS members split between a more GFS solution or a more
ECMWF solution. With the spread between the models remaining more
or less unchanged from what the previous forecast had, this
forecast did not change much either, with the heaviest snowfall
currently forecast to fall from SW MN up through the Twin Cities
toward Rice Lake and Ladysmith in WI. For headline changes, we
expanded it in space to include most of the counties where the
50th percentile snow totals from our experimental snow
probabilities exceeds 6 inches. In addition, we pushed the end
time out to 6z Saturday for the entire watch to account for
continued strong winds and slowing of precip departure in models
into Friday evening.

The key to the model differences for snowfall totals comes from
where the initial warm advective precip sets up. Our northern and
southern solutions are closely tied to how far north each model
brings precip up Thursday night. The forcing difference is subtle,
but looks to be tied to a northern jet streak over Lake Superior
Thursday night into Friday morning. The ECMWF does not lift this
feature and its associated right entrance region as far north and
west as the NAM or even the GFS. We`ll see a strong dryslot moving
in, which may lead to a brief weakening in precip during the
morning, before the deformation precip with the upper wave moves
through. Further aiding in the higher totals seen with the GFS is
the fact that it closes off an h5 low, whereas the ECMWF continues
with a more open wave and progressive system, which helps to keep
its snow farther south. Still, no matter where the primary band
sets up, the forcing with this system is impressive, especially
with the initial band of precip coming up Thursday night into
Friday morning. Forecast sounding show steep midlevel lapse rates
sitting atop strong fgen in the h85-h7 layer, which will likely
support snowfall rates in the neighborhood of 2" per hour. The
forcing with the deformation band is not as strong, but will lead
to a prolonged period of moderate snow from Friday afternoon into
the evening. GEFS probabilities for more than a foot of snow are
around 90% just south of the Twin Cities, hence where the
confidence in seeing snowfall totals in excess of a foot comes
from, its just a question at this point of that occurring across
more south central/southeast MN or across the heart of the Twin
Cities metro.

Beyond this system, where snow cover ends up will become key to
the temperature forecast. For example, the ECMWF, which produces
no snow in west central and central MN, has highs punching back up
into the 40s in the snowless areas by Monday. There is also a lot
of uncertainty with a potential precip maker next week. Here the
GFS is weak/progressive and has a minor precip event moving
through Monday night, while the Canadian and ECMWF are hinting at
the potential for another winter storm Tuesday into Wednesday.
This looks to be a warmer system, with a rain south/snow north
type setup, but will be something to watch as we clean up from
Friday`s system.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 525 AM CST Wed Feb 22 2017

No aviation concerns through the early afternoon as VFR
conditions continue with some -shra in central Minnesota during
the late morning/early afternoon. Deeper moisture will develop
late this afternoon across central Minnesota which may allow for
more shower activity then currently forecast. Otherwise, VFR
conditions will become MVFR/IFR overnight as a cold front moves
south across the area. Winds will start light and variable, with a
more north/northwest across west central/central Minnesota this
afternoon, and across the rest of southern Minnesota, west central
Wisconsin tonight.


No additional concerns with MVFR cigs developing this evening,
with possible IFR cigs toward midnight. Light southeast wind will
become more northeast, north this afternoon and tonight.


Thu...VFR. CHC MVFR/-RA in the afternoon, then LIFR/+SN likely
Thu night with several inches. Wind NE 10-20 kts.
Fri...LIFR. +SN/BLSN. Significant accums. Wind N 20G35kt.
Sat...VFR. Wind NW 10-15 kts.


WI...Winter Storm Watch from Thursday evening through Friday evening
     for WIZ014>016-023>028.

MN...Winter Storm Watch from Thursday evening through Friday evening
     for MNZ044-045-049>070-073>078-082>085-091>093.



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