Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 200021

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
721 PM CDT Mon Oct 19 2020

.UPDATED for 00Z Aviation Discussion...
Issued at 712 PM CDT Mon Oct 19 2020


.SHORT TERM...(This evening through Tuesday night)
Issued at 415 PM CDT Mon Oct 19 2020

Confidence is high that many will see their first accumulating
snowfall of the season on Tuesday. As such a Winter Weather Advisory
has been issued for much of the forecast area.

Any lingering snow showers will dissipate this evening giving way to
overcast skies overnight. The accumulating snow is the result of a
shortwave trough that will move out of the Rockies into the Northern
Plains over the next 24 hours. Morning Forecast models have come
into better agreement with QPF amounts and placement helping
increase confidence in snowfall totals. Low level warm air advection
will strengthen overnight with an initial frontogenesis band of
precipitation starting around 12z in western Minnesota and moving
northeast toward the Twin Cities by 14-16Z. Initial precipitation
may be a mix of drizzle and light snow before heavier returns
changeover to all snow. Beneficial upper level divergence, broad WAA,
and FGEN will combine to produce a swath of 0.40" to 0.70" QPF. Snow
ratios will start around 9:1 and lessen to 8:1 toward the end of the
event as WAA warms the boundary layer. Surface temperatures are
still warm, but snowfall rates will allow for accumulation. Peak
rates appear to move into the Metro after 17Z through 23Z. With all
of that accounted for, forecast snowfall amounts of 2" to 5" seems
reasonable for most. A few areas could locally see 4" to 6" but that
will depend on where the forcing is maximized allowing for heavier
snowfall rates and slightly higher ratios. After 00z drier air will
work into the back edge of system and a period of drizzle or
freezing drizzle will be possible with no additional impacts

.LONG TERM...(Wednesday through Monday)
Issued at 415 PM CDT Mon Oct 19 2020

Wednesday will be dry for most areas with temperatures in the mid
to upper 30s. A strong upper level wave will cause an area of low
pressure to develop and move into the region on Thursday. Models
have come into better agreement for Thursday`s system with rain
showers likely as a low pressure passes through the upper MS
valley. Frozen precipitation will stay to our north as
temperatures warm into the upper 40s to mid 50s near the IA/MN

Colder air will move in behind the departing low Thursday night into
Friday as an area of high pressure settles in for the weekend.
There is a signal for another significant weather system on
Sunday, however with two significant systems ahead of it, I will
give a broad overview of the potential set up. There was partial
agreement between the 12z model suite for a include a negatively
tilting trough that weakens as it reaches MN. The ECMWF/GEM/UKMET
are in agreement with a slower and strong solution that takes the
low pressure from the Rockies through IA and WI. This solution
would result in our forecast area being in the cold sector with
potential snowfall. Again, this will continue to evolve in
subsequent model runs. Below normal temperatures will remain in
place into early next week.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 712 PM CDT Mon Oct 19 2020

Clouds will linger across the region overnight as the winds become
easterly in advance of the next weather system. This system will
bring moderate to heavy snow across the region on Tuesday that
will spread from west to east in the morning, and be heaviest in
the afternoon. IFR/LIFR visbys are possible at times with this
snow. The snow should end toward evening, and could mix in with
rain at times as it tapers off.


Did speed up the onset of the snow by about an hour, and now have
it starting around 15Z. Once it starts, it could quickly go from
VFR to IFR/LIFR within an hour as the heavier snow moves in. Do
expect the snow to be falling heavy enough to accumulated on the
pavement, but then have the snow mixing in with rain Tuesday
evening and ending overnight. Low clouds will continue overnight.

Wed...MVFR/IFR cigs likely. Wind NW at 05-10 kts.
Thu...MVFR/IFR. SHRA likely and TS or RASN possible. Wind NE
10-20 kts.
Fri...VFR with RASN/MVFR possible early. Wind NW 10-20 kts.


MN...Winter Weather Advisory from 10 AM to 10 PM CDT Tuesday for
     Kanabec-Le Sueur-Mille Lacs-Morrison-Ramsey-Rice-Scott-

     Winter Weather Advisory from 7 AM to 7 PM CDT Tuesday for Blue
     Earth-Brown-Chippewa-Douglas-Kandiyohi-Lac Qui Parle-McLeod-
     Stevens-Swift-Todd-Watonwan-Yellow Medicine.

WI...Winter Weather Advisory from 10 AM to 10 PM CDT Tuesday for
     Pepin-Pierce-St. Croix.

     Winter Weather Advisory from 1 PM Tuesday to 1 AM CDT Wednesday
     for Barron-Chippewa-Dunn-Eau Claire-Polk-Rusk.



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