Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 192103
AFDMPX

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

.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
hours.

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 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1148 AM CST Mon Feb 19 2018

MVFR to IFR conditions are expected to continue through most of
the TAF period due to reduced visibilities caused by precipitation
as well as low ceiling heights. North-northeasterly winds will
remain sustained near 10 to 15kts through the evening hours with
continual chances for light snow. There is expected to be a break
in the continuous precipitation during the late evening and very
early hours of Tuesday before another steady band of precipitation
builds in from the west-southwest over the area. During the
break, visibilities will improve but ceilings are anticipated to
remain low below 30kft.

This following precipitation band is expected to produce snow for
West Central MN, however a period of sleet is possible for the
MKT-MSP-RNH-EAU area before precipitation turns completely over to
snow. By the end of the TAF period (18Z Tuesday), visibilities
will improve across Western MN but ceilings are anticipated to
MFVR. Otherwise, winds will remain predominately north-
northeasterly to northeasterly through the remainder of the TAF
period before winds back to out of the northwest in Western MN by
the end of the TAF period.

KMSP...We start this TAF period with MVFR ceilings and IFR
visibilities with light snow. Conditions are likely to improve
slightly this evening before degrading again early Tuesday with
another band of precipitation. A period of sleet is possible
during the mid-morning hours Tuesday before transitioning to snow.
Precipitation will likely end by 18Z Tuesday, but ceilings are
anticipated to remain MFVR through Tuesday afternoon. In
addition, winds will back to out of the northwest during the
afternoon on Tuesday.

/OUTLOOK FOR KMSP/
Wed...VFR. Wind W 5 kts.
Thu...Mainly VFR. Chc MVFR/-SN late. Wind SE 5 kts.
Fri...Chc MVFR/-SN. Wind variable less than 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST Tuesday for WIZ014>016-
     023>028.

MN...Winter Weather Advisory until noon CST Tuesday for MNZ041>045-
     047>070-073>078-082>085-091>093.

&&

$$

SHORT TERM...JLT
LONG TERM...SPD
AVIATION...AMK



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