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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1207 am CST Thursday Dec 25 2014

Update...
issued at 1150 PM CST Wednesday Dec 24 2014

Updated to include 06z aviation discussion below.

&&

Short term...(this evening through thursday)
issued at 354 PM CST Wednesday Dec 24 2014

Regional satellite imagery had shown the lower clouds/ceilings across
South Dakota/NE slowly eroding from SW to NE as winds shift to the SW.
However...the next storm system has already spread middle/high level
cloudiness across the Dakotas and into Minnesota during the afternoon.
Although we could see some breaks in the lower clouds/ceilings late
tonight from SW to NE...overall it will remain cloudy for this
short term period. If we do get a chance of partly cloudy skies...it
will occur in far southern Minnesota as greater mixing in the boundary
layer develops.

As for chance/S of snowfall...there remains a good probability of a
small band of 1-3" to fall across wc into portions of central Minnesota
during the daytime hours. The best chance based on stronger frontal
energy will occur in wc Minnesota. In addition...snowfall ratios will be
initially low in the 8-1 range...plus a warm ground from recent
above normal temperatures...should limit snowfall totals. If the forcing
increases from the current model runs...there could be locally
higher amts. Temperatures from wc to central Minnesota will be the coldest as
precipitation and denser cloud cover will prevail. In SC
Minnesota...temperatures may approach 40 degrees if some sun develops.

Long term...(thursday night through wednesday)
issued at 354 PM CST Wednesday Dec 24 2014

Biggest concern in the long term is snowfall potential inherited
from the short term Thursday afternoon that will continue through
Friday night. After that...the European model (ecmwf) in particular is hinting at
another quick hit of snow Monday before the Arctic air arrives to
end 2014.

For Thursday night through Friday night...an upper trough working
across The Rockies on Thursday will eject northeast across the
plains as a positively tilted trough Friday that will be getting
sheared out as it gets absorbed into northern stream energy across
Canada Friday night. At the surface...the upper low will lead to Lee
cyclogensis on Thursday over Colorado...with a cold front working into
western Minnesota. This front will stall out across Minnesota into far northwest WI Thursday
night as a wave works north along the front into Iowa on Friday.
At the very least this weather pattern will ensure that we
maintain the overcast skies through Friday night...but could also
result in another prolonged period of precipitation starting Thursday
afternoon and lasting through Friday night. The precipitation would start
Thursday as the warm air advection band pushes into western and central Minnesota. This band
looks to slowly diminish overnight as ridging builds in
aloft...helping to break down moisture and lift along the 295k
surface. After that...for much of Friday we get into another potential
drizzle setup as upper forcing moves away...but low level forcing
increases with the trough moving across the area. Temperatures
will be a couple of degree cooler for Friday as well...which means
any dz would be in the form of fzdz. Not overly confident though
on drizzle potential Friday...so simply limited snow chance
mention to 30% or less...but this will obviously need to be
reevaluated. After that...12z models have come into good agreement
on another band of snow working up from south central Minnesota into
central WI in response to whats left of the main upper trough
working across the region as it gets absorbed by the main northern
stream energy across southern Canada. Again moisture looks
limited...but all guidance show this being another band of 1-3
inches of snow wherever it falls. The Friday night band looks to
fall a hundred or so miles south of the Thursday/Thursday night band...so
there will likely be a strip in between that sees very little.
Right now...this strip of little/nothing looks to encompass much
of the Twin Cities metropolitan area.

After that...models continue to be all over the place when it
comes to snow potential as the Arctic boundary comes into the
area. The problem comes with how far east energy will make from a
deep trough that will be digging across The Rockies sun/Mon. The
Gem/GFS take a clipper type snow from the western Dakotas to northwest MO
sun/Mon...while the European model (ecmwf) takes this snow from the western Dakotas to
across southern Minnesota. Given the amount of movement we have seen in the
models with this snow...limited probability of precipitation to Sunday night and across
southern Minnesota. After Monday...its into the freezer with the active
weather looking to largely avoid the upper MS valley for a while
as southern stream energy stays down along the Gulf Coast while northern
stream energy remains mostly in Canada.

For temperatures...there will be two temperature drops this
period. The first will come behind the Friday front...this will
send highs back down to about normal for the weekend. The Arctic
boundary arrives Monday...but there continues to be disagreements
on when that arrives...with the GFS bringing in the Arctic air
Sunday night...with the European model (ecmwf) waiting until later Monday.
Continued to favor the warmer European model (ecmwf) solution given the fact that
each successive run of the GFS delays to the Arctic airs arrival
some...and with little in the way in snow cover south of
Canada...the colder air will likely be bit delayed in getting
here. As for that cold air...the core if it actually looks to go
west of Minnesota out across the High Plains as a 1050 mb high builds
south along the foothills of The Rockies. Still...with 925-850
temperatures forecast to be between -16c and -20c by new years evening...it
still looks good for a rather chilly final day of 2014 with highs
likely staying in the single digits...even if we do not have much
snow cover.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1152 PM CST Wednesday Dec 24 2014

IFR ceilings across much of Minnesota. Already have middle clouds moving into
west central Minnesota and the southwest wind on the backside of
retreating ridge and incoming cold front is scouring the low
clouds over western central Minnesota. This may work into krwf and kaxn
next hour or so...lifting to VFR for at least a few hours.
Elsewhere...the IFR clouds are moving to the east in the southwest
low level flow. This may work farther east into west central
Wisconsin overnight into Thursday morning. Otherwise...snow threat
increasing over the northern County Warning Area during the day. Could mix with
drizzle or light rain during the day as boundary layer
temperatures remain near critical values. Should change over to
snow as better lift moves through central Minnesota during the day.
Forcing associated with the northern stream jet streak exits the
area into the evening and may generate a lull in any precipitation
at least early into the night before more forcing moves in from the
southwest. MVFR to IFR ceilings looks likely again into the night most
areas. Southwest to south winds ahead of the front...a bit breezy
to the southwest...before the front sags south into the area.
Surface winds light becoming NE-north with passage of the front.

Kmsp...low end MVFR to ifs ceilings into the morning. Believe any
significant threat of snow will remain north of the Airport
through at least 23z. Then as front sags in...we could see some
-sn into the evening...but is not to be significant. Mentioned
prob30 for this potential. Ceilings are expected to drop off through
low end MVFR again at least into the coming night. SW-S winds
during the daytime...10kts or less. Then with frontal passage...expect winds
to turn more east-NE and the north later tonight.

/Outlook for kmsp/

Friday...MVFR/IFR with chance -sn. Winds north-northwest 10 kts.
Sat...VFR. Winds west-northwest 5-10 kts.
Sun...VFR. Winds south-southeast 5 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

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

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