Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 101039
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
439 AM CST Tue Jan 10 2017

.SHORT TERM...(Today and tonight)
Issued at 415 AM CST Tue Jan 10 2017

Today and tonight...Complex next 12-24 hours as one area of low
pressure swings northeast from northwest IA into the northern Great
Lakes by this evening and into Hudson Bay by daybreak tomorrow,
followed by another low pressure center developing low pressure
center over southern MT pushes through SD and arrives into northwest
IA tomorrow.

Areas of sleet and freezing rain are currently moves east northeast
through western and southern portions of the coverage area this
morning and will continue moving ENE through late morning as the low
pressure center moves into southern MN. As the day progresses,
deeper colder air will entrain within the system which will allow
the p-type to transition back to all snow. In addition, a trough
axis aloft helping to pick up and enhance the surface low will
become slightly negatively tilted which will enhance lift for the
system as it moves into northwest WI. These evolving features will
help enhance snow rates from far eastern MN into western WI, such
that rates of around 1/2" per hour may well be realized from time to
time over far western WI. This will push the snowfall accumulations
higher in this portion of the coverage area, likely into the 2-4"
range but potentially up to around 5" for some isolated locations in
western WI before all is said and done by early this evening. The
other concern with this system is that wind speeds will noticeably
increase on its back side, increase to the 20-kt range with some
higher gusts, mainly over western and southern MN. With fresh snow
falling just when the winds increase, this may well cause some
blowing/drifting snow concerns, particularly for the I-90 corridor.
Thus, after collab with surrounding offices, have issued winter
weather advisories for much of southern MN to account for the icy
precip transitioning to the snow and blowing snow concerns, and for
portions of western WI which look to be susceptible to snowfall
amounts in excess of 3".

The precipitation will wind down by this evening for much if not all
of the WFO MPX coverage area but the break in the precipitation will
not be long as another incoming low pressure system will take a
similar track (akin to a clipper-like track) into the region from
MT. Light snow looks to resume after midnight tonight, taking on a
showery nature at the onset, then steadily increase in coverage
along with becoming a more solid light snow by daybreak. Not looking
for much in additional accumulation after midnight, generally less
than inch, but this will precede potentially higher amounts during
the day tomorrow as addressed in the long term discussion.

As for temperatures, today will be the last day of the mild
temperatures for the area. With the track and upper air pattern
following today`s low pressure system, a more pronounced
northwesterly flow will develop behind the system, leading to the
start of strong cold air advection for later in the week. Highs
today will range from the upper teens in western WI to around 30 in
western MN. Lows tonight will drop back to the single digits above
and below zero.

.LONG TERM...(Wednesday through Monday)
Issued at 415 AM CST Tue Jan 10 2017

The main change in the long term was to further increase Pops, QPF
and snow amounts on Wednesday.  By early Wednesday morning, a weak
area of low pressure developing across eastern CO/western KS will
enhance low level southerly flow toward the Upper Midwest, meaning a
decent baroclinic zone will be across central MN to northern Iowa.
Meanwhile, the jet structure is becoming more apparent as we get
closer in time and will enhance lift across our area as well during
the day.  A 150kt jet streak will lift northeast of the forecast
area, placing us within a favorable area of upper level divergence.
This combined with modest lift along the best F-gen and Fn vector
convergence zone gives us more confidence in a high ratio snowfall.
The area of ascent will move through and produce a 1-2" snowfall
with the best potential for exceeding 2" in northwest WI.  This will
be the last round of 3 separate bouts of light snow accumulations
this week.

Cold northwest flow will follow to end the week and there was really
no change in the outlook for Thursday night.  Basically continued
the same overnight low forecast with a very strong area of high
pressure overhead by early Friday morning. Lows in the teens to 20s
below zero are expected.  In terms of wind chill, with the high
overhead it may not be all that different from the actual air
temperature.  Very light/calm winds are expected Friday morning.
Warm air advection on the backside of the departing high is prompting
the GFS and EC to produce very light QPF along I-90 Friday night
into Saturday.

Temperatures will warm each day from there and the EC wants to bring
another bout of precip into southern Minnesota Monday morning, but
the GFS indicates this activity staying to our south.  Will keep an
eye on how this evolves as we get closer in time.  One thing for
sure though, is the warming trend into next week.  The guidance
agrees on a zonal flow pattern meaning moderating temperatures that
will likely be above normal for most or all of next week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 654 PM CST Mon Jan 9 2017

Light snow will be possible through most of the period at the TAF
sites, but the main window for snow that will accumulate and lower
vsbys will be after 11z Tuesday. Other than a brief scattering in
the low cloud (MVFR) deck from central MN into west central WI
this eve, expect MVFR and IFR cigs to become prevalent overnight,
with vsbys lowering to IFR with the snow on Tuesday as well.
Southeast winds 08-15 knots with gusts into the lower 20s shift to
northwest Tuesday with gusts into the mid 20s developing.

KMSP...
Other than the possibility of flurries, precip has ended until the
early morning hours. May see a bit of a wintry mix prior to
daybreak, but we are more confident on the snow which will arrive
around 12z. Cigs/vsbys will be prevalent mvfr with the snow with
occasional reductions during the morning to around or slightly
below 1SM (similar to today). The snow should taper off by 00z
Wed. Southeast winds with gusts to around 20kts this eve become
lighter and variable by daybreak, the shift to the northwest by
the afternoon and increase. Expect gusts to around 25 kts during
the afternoon.

/OUTLOOK FOR KMSP/
Wed...VFR. MVFR with -SN possible late. Wind W 5-10 kt bcmg N.
Thu...VFR. Wind NW 5-10 kt.
Fri...VFR. Wind variable 5 kt or less.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for WIZ016-
     027-028.

MN...Winter Weather Advisory until 6 PM CST this evening for
     MNZ073>078-082>085-091>093.

&&

$$

SHORT TERM...JPC
LONG TERM...SPD
AVIATION...LS



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