Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 121022

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
422 AM CST Tue Dec 12 2017

.SHORT TERM...(Today and tonight)
Issued at 422 AM CST Tue Dec 12 2017

A weak surface high pressure ridge to start the day will be quickly
replaced by the arrival of a low pressure trough tonight. Clouds
will increase notably by mid-day as isentropic lift develops east of
the warm front aligned along the MN/Dakotas border. This is first
noted across central MN by 18z, and then gradually drifts
east/southeast during the evening. Have therefore included 20-30
POPS. Temperatures will moderate into the low/mid 30s along the
Minnesota River Valley, with areas to the east seeing cooler highs
in the 15 to 25 degree range. Have also increased lows for tonight
given west/southwest flow ahead of the approaching trough and
clouds should limit radiational cooling.

.LONG TERM...(Wednesday through Monday)
Issued at 422 AM CST Tue Dec 12 2017

The potent upper wave dropping south into the Upper Mississippi
Valley Wednesday morning will become more neutrally tilted by
midday. This, with continued isentropic lift, will strengthen the
snow band from west central WI southeastward at the beginning of
the period. Models haven`t been displaying the best consistency
with the placement and intensity of the snow with this system so
confidence isn`t the best. It is possible 2 to 4 inches could fall
under that band before the system shifts to the southeast by

Another issue to contend with is freezing drizzle. The surface low
will pass over eastern MN late tonight and Wednesday morning with
the mid level dry slot accompanying it. Somewhat deep low level
moisture extending up to 7kft with some lift through that layer
could generate areas of freezing drizzle. This risk will be
enhanced during the late morning as strong CAA steepens low level
lapse rates and the moisture layer becomes unstable. The low
levels will be warm enough that this moisture won`t extend into
the DGZ until afternoon when the column cools. Therefore, the
forecast for most of the Minnesota counties calls for a chance of
snow initially given the uncertainty in placement of the morning
snow band, followed by a chance of freezing drizzle as the mid
level dry slot moves in, and then back to a chance of snow showers
during the mid to late afternoon with reintroduction of ice
aloft. There shouldn`t be too much ice accumulation, if any,
especially with temperatures rising to near freezing by late

Strong winds are expected again behind this clipper, mainly across
western and southern Minnesota. Forecast soundings are quite a
bit more impressive with wind gust potential with this one than
with the one for Monday. GFS Bufkit soundings show mixed layer
gusts ranging from about 40 kt in the lower levels to 50 kt at
the top of the mixed layer. NAM is even stronger at the top,
reaching 55 to 60 kt. A Wind Advisory will eventually be needed,
but a High Wind Warning may also be possible if later trends favor
the NAM.

The clipper train continues later in the week, but predictability
with each of these disturbances is low at this range. Maintained
low chance PoPs for now.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1128 PM CST Mon Dec 11 2017

Skies will be mostly clear overnight, with the exception of
lingering clouds circa 3KFT in west central WI, and an eventual
increase in mid level clouds around 10kft from the northwest.
Another batch of low clouds with MVFR ceilings looks to move into
the northwest (KAXN) on Tuesday morning, likely shifting into the
other sites Tuesday afternoon. Light snow showers will be possible
as well, primarily at northern sites (KAXN-KSTC) during the day,
then in west central WI (KRNH-KEAU) during the evening.

Mostly clear skies overnight and then a broken mid-level deck
arrives Tuesday morning. The potential for MVFR cigs (and
flurries) is the highest between 20z Tues and 00z Wed.

Wed...MVFR with chc -SN. Wind SE 5 kts mrng, NW aftn 10-15 kts.
Thu...Chc MVFR. Wind NW 10-15 kts.
Fri...Chc MVFR. Wind WSW 5-10 kts.




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