Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 200517

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1117 PM CST Mon Feb 19 2018

Issued at 739 PM CST Mon Feb 19 2018

Just finished a significant update to PoPs for the rest of
tonight. We are in a "lull", but we are not anticipating the
current situation of widespread light freezing drizzle and snow to
end before the next wave gets here after 6z, so basically dropped
80+ pops in for the rest of tonight across the entire MPX area.
As for the snowfall forecast, did lower totals by about an inch
for our western tier of counties as the deformation band has setup
just west of our CWA this evening, with the HRRR and HopWRF both
pushing the 4 to 6 inch type snow totals west of the MPX coverage


.SHORT TERM...(This evening through Tuesday)
Issued at 250 PM CST Mon Feb 19 2018

The afternoon regional radar which was overlaid with the day
cloud phase satellite imagery (RGB), showed the wavy elements of
the clouds, which correlated nicely with the higher reflectivity.
These enhanced returns on the radar are related with an elevated
warm air advection regime, and a upper jet core moving across the
Upper Midwest. Although surface observations had only indicated
some light snow, mixed with freezing rain or sleet, I wouldn`t be
surprised to see some of the enhanced returns on radar having
heavier sleet, or some heavier snowfall for the next couple of

The forecast tonight, and into Tuesday morning will be based a
strong short wave moving out of the Rockies, and a pronounced
thermal gradient aloft indicating a mixed bag of precipitation in
the far southeast 1/3 of MPX forecast area.

The precipitation type issue is based on a very pronounced dry
layer initially which coincides with the lack of ice formation in
the clouds. Not until late tonight will the atmosphere moisten up
again to get into the preferred dendritic growth zone region, or
at least cold enough in the moist layer to generate ice vs
supercooled liquid water.

Most models support an increase in lift/moisture in the dendritic
growth zone region after midnight in southwest Minnesota. This area
will spread rapidly northeast across southern/central Minnesota, by
3 am, and into west central Wisconsin by 6 am. Models are also
indicating steeper lapse rates (700/500 MB aloft) developing
overnight. Thus, I wouldn`t be surprised to see some thunder in far
southern Minnesota after midnight. This scenario of thunder is also
supported in the forecast WRF models that have higher reflectivity
moving into southern Minnesota between midnight and 6 am.

Precipitation type is the main concern in far south central,
southeast Minnesota, as well as portions of west central Wisconsin
tonight. This is related to the 0C thermal boundary (Aloft) that
moves northward once again ahead of the next short wave tonight.
QPF amounts are not overly heavy through Tuesday morning, but the
majority of the precipitation occurs in a 3 to 6 hour time frame.
So, locally moderate to heavy snowfall is possible where the best
energy/lift coincides with the dendritic growth zone in west
central/central Minnesota. Where the precipitation type is mixed,
snowfall amounts will be much lighter with a coating of ice from
Albert Lea, Minnesota, northeast to Eau Claire, Wisconsin.

.LONG TERM...(Tuesday night through Monday)
Issued at 250 PM CST Mon Feb 19 2018

The long term period will feature below normal temps for the middle
of the week, a likely light snow event for Thursday night, and
temperatures warming to near or even slightly above normal for the
weekend and into early next week.

By tomorrow evening, the system will have departed to the east, with
the cool down underway.  Surface winds will have turned
northwesterly, and a cool canadian high pressure will be moving in
from the northwest.  Clearing skies and the arrival of a colder
airmass (in addition to fresh snow cover for some of the area) will
allow temperatures to drop below zero for much of the area. With
the high in place for Wednesday, expect plenty of sunshine, but
temperatures held around 15 to 20 in areas with snow. Western MN
and western WI will likely see temepratures 5-10 degrees warmer
due to the bare ground and more widespread tree cover.

Thursday will begin quiet, with the high departing to our east and
southerly winds developing.  Meanwhile, the longwave trough
across the western CONUS will become quite amplified and positively
tilted, putting us in a southwest flow pattern.  By Thursday night,
a shortwave trough will eject from the southwest CONUS on a
northeast course, with a likely light snow event expected.  This
will be a quick moving wave with warm air advection enhancing lift
along with a strengthening upper jet.  It still looks to be a 1 to
3" of snow type of event.

Moderating temepratures will continue from Thursday right into the
weekend as the zonal pattern keeps the bitter cold to our north.  By
the weekend, high temperatures should reach the mid 30s, a few
degrees above normal.  The pattern for the weekend typically means
more active weather for the middle of the country, and another
shortwave does eject from the southwest again on Saturday.  The
models diverge with this system, so currently confidence is low in
its path.  The ECMWF would bring light snow through much of southern
MN, while the GFS keeps it well south.  Following a blended approach
of this with the forecast reading a chance of snow for much of the
area Saturday afternoon-night.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1117 PM CST Mon Feb 19 2018

Next round of precip is rapidly developing down by Omaha. This
looks to have two parts that may go on either side of the Twin
Cities with a band of snow going across southwest into central MN,
with a band of FZRA and PL going across southeast MN toward EAU.
Continued to follow the HRRR for timing which has been pretty
consistent over the last 8 hours. Followed the GFS for timing cig
improvements late afternoon/early evening.

KMSP...HRRR has been pretty consistent with an IFR type vis snow
moving in between 9z and 11z. May get an inch out of it, with a
more snow pellet type snow like we saw Monday afternoon. Depending
on how strong subsidence is behind the morning wave, we could see
cigs improve a bit faster than what we have.

Wed...VFR. Wind W 5 kts.
Thu...VFR in mrng, MVFR or lower in aftn. Chc IFR/-SN late. Wind
      SE 5-10 kts.
Fri...MVFR. Chc IFR/-sn. Wind W 5 kts.


WI...Winter Weather Advisory until noon CST Tuesday for WIZ014>016-

MN...Winter Weather Advisory until noon CST Tuesday for MNZ041>045-



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