Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 101759

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1159 AM CST Fri Nov 10 2017

Issued at 1150 AM CST Fri Nov 10 2017

Updated to include 18z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 348 AM CST Fri Nov 10 2017

A very cold and dry air mass was overhead this morning, and it
will be slow to move out of the region today. This will set the
stage for the main forecast concern as to whether increasing
isentropic lift can saturate the atmosphere before it moves out of
the area, limiting snowfall potential.

Satellite and surface observations does support moisture in the
4-6k range moving rapidly northeast across Nebraska, and into
South Dakota. This is in response to the increasing low level
jet/moisture advection that is expected to move across the Upper
Midwest this morning. Above this layer, moisture rapidly dries
out, then moistens up again above 15k. The layer between 6k and
15k will initially be very dry until late this afternoon as strong
isentropic lift in this layer begins to strengthen.

This is a rapidly moving system which is another concern as the
atmosphere begins to saturate, will there enough lift to support
light snow reaching the ground before it moves out of the area. The
best potential of both saturation and the continuation of lift in
the saturated column to support light snow, will be in west central
Wisconsin late this evening. Further to the west, and once the
atmosphere saturates, most of the lift will have moved out. It does
seem to indicate that the weather models have sped up the saturation
faster than in previous runs. Therefore, this forecast could be
altered some to support light snow, with minor accumulations in east
central Minnesota this evening. Later shifts can re-evaluate once
the atmosphere begins to saturate and light snow reaches the
surface. Otherwise, the forecast is on track for temperatures to
hold or even begin to rise tonight as much warmer air moves over the
Upper Midwest.

.LONG TERM...(Saturday through Thursday)
Issued at 348 AM CST Fri Nov 10 2017

Forcing and moisture will be shifting east of the area by Saturday
morning, with drier air and clearing skies expected by afternoon.
A cold front should go through during the late afternoon, but
advection behind it will be weak enough to preclude a drop off in
temps. Highs Saturday will range from the mid 30s to lower 40s.

High pressure will drift overhead Sunday and Sunday night. Milder
air will accompany this ridge compared to the one currently
bringing January temperatures to the region. We should see
increasing high clouds and return flow develop late Sunday night.

Southerly flow will be in place through Tuesday. Temperatures
Monday will finally return to normal, but will exceed normal
values by 10-15 degrees Tuesday. Thermal ridging snaking up ahead
of another approaching cold front may send highs into the
mid/upper 50s if those +8 to +10C 925 mb temps pan out during the
afternoon. The front will pass through Tuesday evening, with
enough moisture finally arriving to break out some precip across
the WI counties.

A mild pacific airmass will follow the cold front, so not
expecting any drastic downward trend in temps late week. A much
stronger system appears to eject eastward across the Pacific
Northwest sometime late next week with the GFS, GEM, and ECMWF
strengthening the cyclone into the mid 970s mb at some point
during its trek across the Midwest/Great Lakes region. Temporal
differences are quite vast, however.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1150 AM CST Fri Nov 10 2017

VFR conditions for the first portion of the TAF then conditions
expected to deteriorate somewhat this evening into the early
morning hours in advance of a cold front approaching for Saturday.
Snow showers to develop over north-central MN then spread
southeast through eastern MN and western WI this evening and
tonight, mainly north of I-94. Most spots to remain as VFR
although MSP and eastward may well be reduced to MVFR due to
ceilings (with the WI TAF sites possibly seeing steady enough -SN
for MVFR visibilities). Duration will not be long, essentially
exiting by 12z tomorrow morning with VFR conditions to resume.
Gusty SE winds to continue into the evening hours then settling
down overnight and slowly veering to SW and W.

KMSP...Have currently only advertised VFR-visibility -SN but
should the swath of -SN dip a little further S and become
prolonged, visibility could well drop to the 3SM-4SM range for
possibly a couple hours. At this point, went with the more
optimistic 6SM and hinted at the degraded conditions but will
need to see how the -SN develops later before reducing conditions
any further. Ceilings are expected to remain above 2000ft but
cannot completely rule out ceilings a bit lower.

Sun...VFR. Wind NW 5-10 kts.
Mon-Tue...VFR. Wind S 5-10 kts.
Wed...VFR. Wind NW 5-10 kts.




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