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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
535 PM CST sun Feb 7 2016

Update...
issued at 535 PM CST sun Feb 7 2016

Updated to include 00z aviation discussion below.

&&

Short term...(this evening through monday)
issued at 225 PM CST sun Feb 7 2016

Several concerns over the next 24 hours as a blizzard & Winter
Storm Warning takes effect in the next few hours.

First...

Updated earlier on the delay of the Blizzard Warning in parts of SW
Minnesota due to very mild temperatures during the day and snowfall hadn/T
materialize. Plus wind speeds have not yet become strong enough to
create the blowing snow where a crust on the snowpack had occurred.
Other areas that have a Winter Storm Warning and/or advisories in
effect tonight remain fine due to significant blowing snow still
expected...but likely not until later this evening.

Current regional radar and water vapor imagery indicated a potent
short wave moving southward across northern Minnesota this afternoon. This short
wave will be the main factor of generating snowfall this evening.
Plus...the dendritic zone deepens quite rapidly behind the Arctic
front that was Colorado-located with the short wave. Although the wind
speeds have not developed as strong as previously indicated as of 2
PM...these winds will likely develop this evening once this short
wave moves through. Again...it is more of a delay of the blizzard
conditions in SW/SC Minnesota tonight. As previously stated...the dendritic
growth zone deepens enough that with any moisture riding southward on
the upper level storm system...periods of light snow will occur.
Although quantitative precipitation forecast amts will be light and under a tenth of an inch. A good
area of 1-2 inches of snow is likely by Monday morning for most of
central and eastern Minnesota/western WI...with amounts less than 1 inch in
SW/wc/SC Minnesota.

As per wind speeds... area model soundings develop a dry adiabatic
lapse rate between the surface...up to 90/85h. With this type of
sounding...momentum Transfer will be maximized from winds on top of
the this steep lapse rate. Therefore...as the short wave moves
through and stronger winds aloft begin to mix down...much stronger winds
will develop...leading to blizzard conds.

Expect the strong winds to continue through noon on Monday. The pressure
gradient should begin to lessen by Monday afternoon...decreasing the wind
speeds. Although blowing snow will continue as wind gusts of 30 to 40
miles per hour will likely hold through the afternoon.

Long term...(monday night through sunday)
issued at 225 PM CST sun Feb 7 2016

The longer term concern is timimg of any snow moving along the
baroclinic zone off to the west of the area...as the upper air
pattern becomes amplified with the eastern Continental U.S. Trough and ridge
to the west.

Any snow showers/flurries and patchy bloming snow will come to an
end Monday night over the County Warning Area. Some clearing is likely in the wake
of the system. Where it does clear...temperatures should be able
to cool through the single digits to around zero in central Minnesota.

The surface ridge builds across the area Tuesday and lingers over
the area through the work week. 850 mb temepratures remain generally
minus 15 to minus 20 over the eastern half of the County Warning Area. This should
provide the cooler than normal temperatures the cfs has been
shwooing the last several runs. The deterministic runs continue to
have some run to run discontinuity problems with any possible
light snow band that is generated with any weak impulse that works
over the western ridge. Have opted to continue the dry forecast
for the week as the surface ridge dominates. As the eastern trough
translates farther east into the weekend...we should see a slow
warming trned along with a chance of snow returning to the area
about Sunday or so.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 535 PM CST sun Feb 7 2016

Forecast hasn/T changed much from earlier... with a lot of
uncertainty remaining in the degree of blowing snow and reduced
visibilities we/ll see. The Arctic front has made it through most
of the area... and will continue to drop southeast this evening.
Strong northwest winds are developing... with gusts at or above 30kt
already in place across the north/west portion of the area.
Expected wind gusts overnight into Monday morning would certainly
support blsn and low visibilities at times. However... today/S
warm temperatures and melting combined with the quick-freeze this
evening could work to put a crust on things and lock that snow in
place... meaning we/ll be dependent on new snowfall to blow
around. It is somewhat of a waiting game at this point... and
we/ll have to see how things develop over the next few hours.
Ceilings look fairly consistent in the MVFR category through the
period as we remain in cyclonic flow with quite a bit of boundary
layer moisture in place. Kept ceilings in place through the period
for now... although some guidance does suggest the potential to
scatter out toward the end of the period. That will be something
to keep an eye on in future updates.

Kmsp...main uncertainty is with the degree of visibility
restriction due to falling/blowing snow as discussed above. Kept
fairly close to going forecast for now... but may need to be more
optimistic depending on how things develop this evening with the
increased wind and light snow expected.

/Outlook for kmsp/
Monday overnight and Tuesday...MVFR ceilings possible. Northwest
wind 15 to 25 knots.
Tuesday night...VFR. Northwest wind 15 to 20 knots.
Wednesday...VFR. Northwest wind 10 to 20 knots decreasing to less
than 10 knots.
Wednesday night and Thursday...MVFR ceilings and visibilities
possible with a chance of snow. Variable wind less than 10 knots
becoming north around 10 knots.

&&

Mpx watches/warnings/advisories...
WI...none.
Minnesota...Blizzard Warning until noon CST Monday for mnz065>067-073>076-
082>085-091>093.

Winter Storm Warning until noon CST Monday for mnz041-047-048-
054>058-064.

Winter Weather Advisory until noon CST Monday for mnz042>045-049-
050.

Winter Weather Advisory until noon CST Monday for mnz051>053-
059>063-068>070-077-078.

&&

$$

Update...
short term...jlt
long term...dwe
aviation...

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