Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 211100

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
500 AM CST Tue Feb 21 2017

.SHORT TERM...(Today and tonight)
Issued at 500 AM CST Tue Feb 21 2017

Status lingers to the north and east of the Twin Cities early this
morning behind a cold front while fog, some dense, cover portions
of central and southern MN under the surface ridge axis.

The day ahead will be a warm one as a low level thermal ridge
works in from the Dakotas during the day along with southwest low
level winds developing. This will push the low clouds off to the
east this morning along with the fog diminishing by 9 am.

The pattern today is very favorable for temperatures to get out
of control. Due to this, went well above mix-down and to the high
end of bias corrected data. This yields highs in the lower 60s
around the Twin Cities as well as on north along the I-35 corridor
with around 60 in west central WI. Middle to upper 60s are
expected in the MN River Valley. This would be another record
setting day. Current records include 55/1961 at STC, 59/1930 at
MSP and 60/1930 at EAU. Highs forecast for today are 58, 62 and 60
respectively. It will be fair and very mild tonight with lows in
the 35 to 40 degree range.

.LONG TERM...(Wednesday through Monday)
Issued at 500 AM CST Tue Feb 21 2017

The winter storm that has been advertised for late this week remains
on track to affect a large area of the Upper Midwest, starting
Thursday evening. Subtle differences in the models continue, but
there is enough confidence that heavy snow will affect a portion of
south central, east central Minnesota, and portions of west central
Wisconsin late this week. Amounts could range from 6 to 12 inches,
with locally higher amounts.

First, a cold front will sag southward Wednesday which will set the
stage for a strong thermal gradient that will aid in the winter
storm. Light rain is possible along this front Wednesday, but areal
coverage will remain low, and most of the energy will be across
northern Minnesota.

An ensemble model (GEFS 21 members) and the CIPS analog guidance
both support a broad area of heavy snow across portions of MPX
forecast area starting Thursday night. The CIPS analog continues to
support a mean snowfall total of over 6 inches along a southwest to
northeast line from southwest Minnesota, into northern Wisconsin. In
addition, the GEFS 21 member ensemble has less spread today in the
6/8 and 12" snowfall amounts in southern Minnesota then in earlier
runs. This again has allowed for confidence to increase on a snow
storm in the Upper Midwest. Using past history from a local study of
winter snowfall climatology, this system is a "typical" Colorado Low
Winter Storm which brings an area of 6+ inches of snow across the
Upper Midwest. The main forecast concern is the initial warm air
advection regime and how far north this develops across Minnesota.
In addition, does this system have two parts to it, which is the
initial warm air advection regime, and the ladder half of the storm
which brings a deformation zone regime of heavy snowfall. Too many
details to discuss, but I would not be surprised to see a watch out
later today or early tonight.

No changes past the winter storm as a colder upper level flow
pattern develops.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1052 PM CST Mon Feb 20 2017

Cold frontal passage on its way through central MN as the rain
has shifted off to the east. Conditions have dropped to MVFR/IFR
with the passage of the front and IFR conditions are likely over
much of the first 4-6 hours of the TAF. Low stratus is evident on
IR satellite behind the higher clouds, but also trailing is a
clearing area in western MN. Conditions will be tricky overnight
since the low stratus/fog currently may give way to a period of
VFR then go back to IFR around sunrise into late tomorrow morning
then go back to VFR for much of the day. The timing may require
multiple amendments but will monitor and adjust as needed. Winds
will shift from SE to WNW with the fropa then back to southerly
with the influx of high pressure. However, speeds will settle down
to less than 10 knots overnight through tomorrow.

KMSP...Slow improvement has been seen from the IFR conditions at
initialization and will look for conditions to hit VFR prior to
the next routine TAF issuance. Still will look for IFR fog to
settle over the area during the time of the morning push, followed
by VFR conditions thereafter.

Wed...VFR. Wind SW at 10G15 kts becoming NW late.
Thu...VFR. CHC MVFR/-RA/-SN in the afternoon, then LIFR/+SN
possible Thu night. Wind NE 5-10 kts.
Fri...IFR or lower in SN/+SN likely. Wind NE 15-25G35 kts.




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