Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 121236 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
636 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 12Z TAFS through 12Z Wednesday morning)
Issued at 636 AM CST Tue Dec 12 2017

VFR early this morning at all MPX TAF sites, but MVFR cigs will
develop later today and a few flurries are also possible north of
I-94. VFR conditions may return briefly tonight before the next
system dives southeast into the Upper Midwest Wednesday. Light
snow and IFR cigs will develop late tonight north of I-94.

KMSP...VFR likely through the morning, with MVFR cigs developing
this afternoon. Some improvement overnight before low level
moisture increases and -SN/FZDZ becomes possible Wednesday

Wed...MVFR/IFR with chc -SN/-FZDZ. Wind becoming NW 15-25G35kts.
Thu...Chc MVFR. Wind NW 10-15 kts.
Fri...Chc MVFR. Wind WSW 5-10 kts.




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