Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 111032
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
432 AM CST Sun Dec 11 2016

.SHORT TERM...(Today and tonight)
Issued at 432 AM CST Sun Dec 11 2016

We certainly ended up with an overachieving mesoscale band of snow
overnight that setup from Redwood Falls over to St. Peter and Pine
Island. Here, the broad area of isentropic precip was aided by a
narrow strip of strong frontogenesis near h7 that remained
stationary for several hours. It is the middle of the night, so we
have yet to get many reports as of writing this discussion, but we
will likely end up with narrow strip of around 10" where this band
setup overnight. After 2am, this heavier band finally started to
lift northeast in response to lift associated with the strong short
wave coming across the Dakotas (as noted by the strong drying seen
on water vapor imagery).

For the headlines, made a few changes in terms of who is in/out and
moved up the end times by several hours.  Based on where the band
setup, we ended up downgrading Lac Qui Parle and Dakota counties
back into the advisory, and trimmed the northern tier of counties out
of the advisory as well (St. Cloud over to Ladysmith) as drier air
really limited the northern push of the snow overnight. As for end
times, now have the western half of MN headlines ending at 9am, the
eastern half of MN headlines at noon, and western WI at 3pm. Though
looking at how quickly drying is moving into SW MN and timing of
snow we are seeing with the HRRR, this is likely still too long to
hold on to headlines.

Going into tonight, the question becomes what happens with cloud
cover. The NAM and GFS are both aggressive with pushing clear skies
across MN during the night as a surface ridge moves into southwest
MN. This results in a big bust potential for the forecast lows
tonight, especially in western MN, where if clear skies do occur,
they will combine with light winds and fresh snow to allow for a
runaway temperature scenario, with lows double digits below zero not
out of the question. Given the uncertainty with cloud cover, stayed
close to a blend of the deterministic models, which at least got
lows down in the 5 to 10 below range out west.

.LONG TERM...(Monday through Saturday)
Issued at 432 AM CST Sun Dec 11 2016

Much of the week looks to be very cold and fairly quiet weather-
wise. However, things are starting to look a bit more interesting
toward the end of the week with respect to a potential storm
system. The initial Arctic surge still looks to move through the
area late in the day on Monday, with perhaps some light snow
accompanying the frontal passage. Strong cold advection will into
early Tuesday, then we`ll wait on a secondary surge of Arctic air
Tuesday night into Wednesday. High pressure will then slowly work
east southeast across the area through Thursday. Temperatures this
week, particularly lows, could easily be colder than forecast
values depending on cloud cover and wind speeds, since we now have
some fresh snow cover over much of the area. So, if anything,
may need to adjust some values downward in subsequent forecast.

The GFS, ECMWF, and Canadian all show return flow and warm
advection beginning to setup Thursday night, with snow developing
from west to east late Thursday night and Friday morning. There
remain some differences in the guidance, and there have certainly
been some significant changes from run to run over the past
several days, but at this point there is reasonable agreement on a
surface low lifting northeast from Colorado into the Great Lakes
region from Friday through Saturday. Both the GFS and ECMWF would
bring a long duration of warm advection snow to the region,
followed by snowfall associated with the deformation zone
northwest of a surface low they take through Iowa and across
southern Wisconsin. Even colder air could work into the area
behind this system, but with things still 5 to 6 days away, can`t
get too carried away with any specifics at this point. But, it
will be something to watch over the coming days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1204 AM CST Sun Dec 11 2016

Minor changes made to the TAFs with the 6z issuance. Heavier band
of snow south of the Twin Cities will remain there for the first 4
hours of the TAF or so, but will lift NE in the morning as wave
currently moving across the central Dakotas comes into MN.
Followed the RAP and HRRR to time higher rate (lower vsby) snows
into terminals currently north of the heavy snow band, which is
currently all terminals but RWF. Other change was to speed up
ending of snowfall outside of STC/AXN this afternoon to a timing
more in line with the RAP/HRRR. Snow will likely linger through
the afternoon across northern MN on the north end of an inverted
surface trough, which is why ending of snow at AXN/STC was
delayed, though this snow may end up north of them in the end.
Low confidence on skies behind the snow, but safest route is to
maintain an MVFR CIG until we see something different.

KMSP...Confidence is high in the snow forecast for MSP, with
heaviest snow (rates of 1/2 to 3/4 inch per hour) expected between
10z and 15z. Lower confidence in how low cigs will be in the wake
of the snow, but kept things optimistic for now with high MVFR,
though IFR cigs are certainly possible for several hours behind
the snow.

/OUTLOOK FOR KMSP/
Mon...MVFR/VFR. Chc -sn late. SW wind 5-10 kts. Bcmg NW 10G20kt
      overnight.
Tue...VFR. WSW wind 10G20 kts.
Wed...VFR. WNW wind 10G20 kts.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 3 PM CST this afternoon for
     WIZ023>028.

MN...Winter Storm Warning until noon CST today for MNZ069-076>078-084-
     085.

     Winter Weather Advisory until noon CST today for MNZ059-060-062-
     063-068-070-093.

     Winter Storm Warning until 9 AM CST this morning for MNZ064-065-
     067-073>075-083.

     Winter Weather Advisory until 9 AM CST this morning for
     MNZ054>058-066-082-092.

&&

$$

SHORT TERM...MPG
LONG TERM...
AVIATION...MPG



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