Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 212333
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
533 PM CST Sat Jan 21 2017

.UPDATE...
Issued at 533 PM CST Sat Jan 21 2017

Updated to include 00Z aviation discussion below.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 200 PM CST Sat Jan 21 2017

Tonight and Sunday...Very damp and mild pattern will persist
through tomorrow as a stacked but unimpressive low pressure system
slowly shifts northeast across the area overnight through Sunday
morning. The deep low will move from southern MN later this
evening into western Lake Superior by daybreak Sunday morning.
This will result in the moist atmosphere remaining in place and
winds going nearly calm later this evening through overnight
before picking up from the NW tomorrow on the backside of this
system. As a result, the northeast winds today to calm winds
tonight along with mild temperatures atop a melting snowpack
within the continued moist atmosphere will maintain widespread fog
with areas of dense fog across the entire coverage area at least
through tonight. With much of the western and southern portions
still dealing with dense fog, to be followed up in eastern
portions later on this evening once the current precipitation ends
with the departing low, have included all of the WFO MPX coverage
area in a dense fog advisory. Southwestern portions will see a
shift in winds to northwesterly tomorrow morning so there is a
chance that these northwest winds will bring in slightly drier low
level air to scour out the moisture and eliminate much of the
dense fog concern earlier than midday tomorrow.

Beyond the fog concerns, light rain has generally diminished
across all of the coverage area, leading to mainly areas of
drizzle through tomorrow morning. In northwest portions, where
overnight temperatures will drop to around freezing, some of the
precipitation may come as freezing drizzle and could present icing
problems around daybreak tomorrow morning.

As for temperatures, much of the coverage area will remain steady
in the middle 30s. However, northwest portions may be subject to
weak cold air advection, just enough to bring temperatures briefly
down to 31-32 degrees before warming back into the mid 30s
tomorrow.

.LONG TERM...(Sunday night through Saturday)
Issued at 233 PM CST Sat Jan 21 2017

The main focus of the long term is the potential winter storm
Tuesday-Wednesday. The forecast for this storm remains mostly
unchanged.

By Sunday night, drier air will continue filtering in and with
decreasing dew points, will likely see most of the forecast area
finally dip back below freezing, especially across western MN
where lows in the 20s are expected. This will allow all the
standing water on the lakes in western MN to freeze. The metro
though, will hover around 32-33 degrees, so we may keep the streak
alive with temps above freezing at MSP.

For the Tuesday-Wednesday system, we are seeing the deterministic
guidance divide into two different camps.  The GFS/EC indicate a
more northerly solution that the NAM/GEM. The GFS/EC both indicate
surface cyclogenesis along the lee of the rockies by Monday
afternoon and a deepening surface low taking its path through
extreme northern MO, through southern Iowa and near or just north
of Chicago. The GEM on the other hand is indicating a southern
track which would keep the precip quite a bit farther south. So,
with little change in the agreement and the spread still in the
ensembles, it wasn`t prudent to make much change to the going
forecast. The southern third of Minnesota still looks to be our
highest potential for snowfall accumulations. Daytime temperatures
above freezing explain the rain/snow mix but that is diurnally
driven. If precipitation rates are strong enough though, snow
would be the primary p-type.

After this storm moves off to our east, the latter half of the week
looks cooler with temperatures below freezing for highs, and
overnight lows in the teens.  We may see some snow showers late in
the week as a trough drops south and side-swipes us as it moves
through the Great Lakes.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 533 PM CST Sat Jan 21 2017

Remained fairly close to previous forecast, with main difference
being somewhat more pessimistic on visibilities for KMSP, similar
to last night. Also lingered lower visibilities longer into Sunday
given fairly good agreement amongst the guidance. With little in
the way of low level wind/advection until Sunday, there isn`t much
reason to expect any widespread or prolonged improvement in
conditions tonight. The west will see improvement first, and the
forecast may be too pessimistic there, but for now persistence
seems to be the smartest play.

KMSP...Main uncertainty in the forecast is with respect to how
quickly visibilities will fall this evening, and how low they will
go. Some amendments will likely be needed, but a more pessimistic
forecast seems reasonable for now.

/OUTLOOK FOR KMSP/
Sunday overnight...MVFR expected, IFR possible. Northwest wind
less than 10 kt.
Monday...MVFR possible early. West wind less than 10 kt.
Monday night...VFR. Variable wind less than 5 kt.
Tuesday...MVFR developing, IFR possible late. Chance of rain and
snow. East wind less than 10 kt becoming northeast 5 to 15 kt.
Tuesday night...MVFR expected, IFR possible. Snow likely, possibly
mixed with rain early. Northeast wind 10 to 20 kt becoming
Northwest.
Wednesday...MVFR expected, IFR possible. Snow likely early.
Northwest wind 15 to 25 kt.
Wednesday night and Thursday...MVFR possible with a chance of
light snow. Northwest wind 10 to 20 kt.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until noon CST Sunday for WIZ014>016-023>028.

MN...Dense Fog Advisory until noon CST Sunday for MNZ041>044-047>051-
     054>059-064>070-073>078-082>085-091>093.

     Dense Fog Advisory until noon CST Sunday for MNZ045-052-053-
     060>063.

&&

$$

UPDATE...
SHORT TERM...JPC
LONG TERM...SPD
AVIATION...


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