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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
612 am CST Tue Dec 6 2016

Update...
issued at 550 am CST Tue Dec 6 2016

Updated to include 12z aviation discussion below.

&&

Short term...(today and tonight)
issued at 335 am CST Tue Dec 6 2016

Surface analysis this morning shows a large rotating low over
northwestern Minnesota while its main cold front is well out in advance
of the center, draped over western WI southward through the mid-
Mississippi River valley. Aloft, a deep upper level low is nearly
atop the surface feature, showing up nicely on WV satellite
imagery. Otherwise, much of the northern-Central Plains
east southeast into the Ohio Valley is under generally zonal
flow, which will make for a progressive nature of the deep low
pressure center. It is expected to drift eastward through the day
into tonight, moving over Lake Superior by daybreak Wednesday
morning. It will slightly deepen as it shifts east, expanding its
range into central Minnesota later today. In addition, a much
tightened pressure gradient on the backside of the low will
develop, in response to dense Arctic high pressure arriving from
northwestern Canada. Thus, the passage of this system will contain
multiple impacts in that it will signal and end to temperatures
above freezing, it will bring in strong westerly winds and it will
bring light snow accumulations for west-central Minnesota. Given
the timing of the increase in winds with the incoming snowfall,
event light snowfall accumulations of 1-2" will be enough to
reduce visibility in west-central Minnesota, mainly affecting
I-94. Therefore, have opted to issue a Snow and Blowing Snow
Advisory for a handful of counties out in western Minnesota. With the
wind speeds still an issue going into southwestern Minnesota, have also
issued a windy advisory since the winds will still be in the 25-35
mph range but just without the snow/visibility restriction. Both
impacts look to subside this evening with breezy conditions
thereafter and little/no additional falling snow. As for
temperatures, cold air advection is certainly ongoing as temperatures in western
Minnesota have dropped to the teens while temperatures in western WI are
still holding in the lower 30s. In fact, today may well be one of
those days where highs are reported at midnight with
steady/falling temperatures for much of the day.

Long term...(wednesday through monday)
issued at 405 am CST Tue Dec 6 2016

The long term forecast has changed very little over the past few
days and that trend continued. By tomorrow morning, the longwave
trough will still be in place across central North America with a
strong low pressure system just north of Lake Superior. Strong
cyclonic flow from this system will continue helping drive cold
air from the north down into the Continental U.S..

The coldest temperatures of the season so far are set to arrive
with the Wednesday-Friday period being the particularly coolest
part of the forecast. And with the aforementioned strong low
pressure system slowly departing to the northeast during this
timeframe, the atmosphere will remain ripe for snow showers and
flurries, especially Wednesday through Thursday owing to the ample
moisture, cyclonic flow and persistent cold air advection.

Continued to nudge pops and winds up above the blend of the model
guidance for this time period. Blended winds just look to low
especially across western Minnesota knowing the persistent cold air
advection should efficiently tap into above ground winds and mix
those directly to the ground. The guidance is trying to indicate
there could be some snow showers during this period, but is not
aggressive enough. We feel snow showers Wed night/Thu especially
are a good bet.

Pops come back into the forecast Saturday-Sunday with a separate
shortwave potentially affecting the area, but the long term
guidance disagrees on how this system will be handled and the
evolution of the overall pattern. The GFS/ec at least both agree
on a warm air advection band of snow moving through as the system
approaches, so included at least chance wording in the forecast.
At this point, quantitative precipitation forecast is not impressive for this period. Looking
ahead to next week, the guidance is indicating the Arctic air
really gathering in Canada and advancing south toward the USA
border hence the climate prediction centers 8-14 day outlook
calling for below normal temperatures.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 550 am CST Tue Dec 6 2016

Low stratus has filled in behind the departing cold front, now
over the Great Lakes, and with the approaching deep low pressure
center from northwest Minnesota. As the low approaches, -sn will move
into western Minnesota later this morning then spread eastward. The
heaviest snow will be in kaxn-kstc...which will also coincide with
strong winds so visibilities may well be less than currently
advertised. The -sn will taper off from all sites by this evening
with a slow improvement in ceilings overnight into Wednesday
morning. Strong west winds of 20-25 kt with gusts as high as 35 kt
can be expected.

Kmsp...main issue will be if kmsp experiences any appreciable
snowfall beyond -shsn. Am expecting snow to remain to the north but
chances cannot be ruled out for some prolonged snow showers
early-mid afternoon. Little, if any, accumulation is expected but
with the breezy conditions, visibilities may be reduced to MVFR
level. (Not expecting IFR level.) MVFR ceilings will be
commonplace throughout this taf set with 1700' ceilings awfully
close to being realized this morning.

/Outlook for kmsp/
Thu...MVFR with slight chance -shsn. NE wind 15-25 kt.
Fri...VFR. West wind 5-10 kt.
Sat...MVFR with chance -sn. Southeast wind 5-10 kt.

&&

Mpx watches/warnings/advisories...
WI...none.
Minnesota...Winter Weather Advisory from 9 am this morning to 9 PM CST this
evening for mnz041-042-047>049-055.

Wind Advisory from 9 am this morning to 9 PM CST this evening
for mnz054-056-057-064-065-073-074-082-091.

&&

$$

Update...jpc
short term...jpc
long term...speed
aviation...jpc

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