Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
139 PM CST sun Dec 28 2014
Short term...(today and tonight)
issued at 333 am CST sun Dec 28 2014
A rather benign short term forecast period is expected...with models
having trended even farther west/south and drier with the shortwave
prognosticated to move across the Central Plains and middle MO River Valley
regions over the next 24 hours. This includes even the most
insistent/aggressive sref with this feature over the last several
days...which is virtually dry in our area with the latest run. Have
removed the chance for precipitation from all counties in the
forecast area except for Martin County...with only a slim
possibility that light snow could scrape southwestern Minnesota between
06z and 12z Monday. Any accumulations would be light...ranging
from a dusting to couple tenths of an inch.
Regarding temperatures...weak northerly flow and cold air advection
will result in a colder than normal late-December day today...as
readings top out from near 15 /kaxn/ to the lower 20s /kael and
Keau/. Should see some sunshine today...primarily during the
The aforementioned wave skirting to the south of the County Warning Area
tonight...while not expected to be a snow-maker locally...should
still supply enhanced cloud cover over south central Minnesota. Therefore
temperatures should be able to hold in the single digits above zero for
Monday morning lows. Farther north /north of Interstate 94/....lows
will sneak to around or even slightly below zero.
Long term...(monday through saturday)
issued at 333 am CST sun Dec 28 2014
A very chilly end to 2014 will start out the long term period...that
still looks like a certainty. Where uncertainty resides is with what
will happen at the end of the period as a clipper coming down Friday
may...or may not try to merge with a deep low coming out of the Gulf
of Mexico this weekend. With the cold...wind chills Tuesday and Wednesday
morning look to get near our Wind Chill Advisory threshold of
-25...while the potential clipper Friday looks to offer US our best
shot at another coating of snow.
First...the big question mark the last couple of days with regards
to tonight into Monday morning was whether or not southern Minnesota would see
some accumulating snow. Well...guidance this morning has come in
with a resounding answer for the snow potential...and that answer is
no. Even the once bullish sref looks like everything else in keeping
any accumulating snows SW of the mpx County Warning Area...so probability of precipitation for Monday
morning were removed. May see some flurries as Post frontal stratus
works across the area...but even here...forecast soundings really do
not support flurries...as although this cloud layer will be in the
dgz...it looks to shallow to get snow going.
For the cold...with a 1055 mb high diving south across the High
Plains and 850 mb temperatures falling to below -20c...there will be no
escaping it. However...with the high remaining off to our west...we
will be maintaining a decent pressure gradient...which will keep the
winds up. This will keep the boundary layer mixed at night...keeping
US from reaching our full potential for overnight lows...but these
winds will lead to some cold wind chills. Current forecast has
apparent temperatures between -20 and -30 c across the western half of Minnesota Tuesday
and across most of the area Wednesday morning.
Tuesday night will see the high sliding east across the Southern Plains.
This will put in motion some pretty good Chinook warm air advection Tuesday night
that will last into Friday. Wednesday will still be cool as we
recover from the very cold conditions on Tuesday...but by Thursday
and Friday...those west winds look to have warmed US enough to get
temperatures back up to near normal.
For the end of the week into the weekend the two features to watch
will be a closed 500 mb low coming out of the 4-corners and a clipper
that will be rounding the base of the deep polar low centered over
Hudson Bay. Thursday night...we will see an Arctic boundary sagging
back into the area...with this baroclinic zone being what the
clipper Friday works with to potentially give US your Standard
clipper 1-3 inches of snow. As this clipper is working across the
area Friday...the southern stream closed low will be coming out over the
Southern Plains...with a phasing of the two systems looking likely by the
weekend. The European model (ecmwf) has come back toward the operational GFS solution
with the phasing taking place Saturday...with a surface low going across
in/Michigan with a nice deformation band of snow coming up across eastern
Iowa...northern Illinois and WI. The parallel run of the GFS looks more like the
previous two runs of the European model (ecmwf)...with this phasing happening much
later...sending the low and its associated precipitation farther east.
Given timing and placement differences with both of these
systems...probability of precipitation never get higher than 30 percent across central Minnesota on
Friday at this point...but this is something to keep an eye
on...especially once the phasing occurs as that should generate a
rather health band of snow to the west of where the surface low GOES.
Behind this system...more Arctic air looks to follow. In fact...that
next round of Arctic air looks to be colder than what we will be
dealing with this week...with the high coming down from Canada up at
1060 mb and 850 mb temperatures closer to -25c. One thing is for sure...the
next two weeks /at least/ certainly look to be the polar opposite of
the weather we had the previous 3 weeks.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 111 PM CST sun Dec 28 2014
MVFR ceilings continue to slowly break up this afternoon. Nearly
all the taf sites should be VFR by this afternoon...and that
should last throughout the night. The exception would be
krwf...where low ceilings in southwest Minnesota could build north
tonight. There is also a slight chance of light snow tonight at
krwf. Otherwise...we just expect middle clouds tonight.
Once the broken 2500-3500ft deck clears this afternoon. Kmsp
should remain in the clear this evening and tonight with no
aviation weather concerns.
/Outlook for kmsp/
Tuesday...VFR. Winds west-northwest 10 kts.
Wednesday...VFR. Winds SW 15g25 kts.
Thursday...VFR. Slight chance of -sn and MVFR. Winds west 5-10kts.