Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
310 am CST Monday Dec 29 2014
Short term...(today and tonight)
issued at 308 am CST Monday Dec 29 2014
Dangerous wind chill temperatures are expected tonight...especially
west of the Interstate 35 corridor.
In the meantime...early morning water vapor imagery shows a
shortwave passing just south of the area. Associated light snowfall
is scraping the southwest corner of Minnesota...missing the mpx
County warning forecast area. In the wake of this wave...skies will clear from north to
south...and set the stage for a cold night as the intrusion of
Arctic air continues. After daytime highs primarily ranging from
around 3 degrees /kaxn/ to around 10 degrees
/kmsp-Keau-kowa/...expect lows to plummet to between 5 below and 15
below. The kicker will be the winds...which will hold up in the 5-10
knot range. The combination of the two will lead to wind chills in
the -20f to -35f range tonight. Have issued a Wind Chill Advisory
from tonight through Tuesday morning for essentially all of the Minnesota
portion of the forecast area...with the exception of far east
central Minnesota /including omission of the Twin Cities metropolitan area/...and
have also kept WI out of the advisory as well. While wind chills in
the Twin Cities and west central WI will dip into the upper teens to
lower 20s below zero...they will not quite reach the -25f
criteria...largely given slightly lower wind speeds.
Long term...(tuesday through sunday)
issued at 308 am CST Monday Dec 29 2014
The long term period is dominated by cold at the beginning...and
uncertainty from Thursday onwards. Though no major systems look to
impact the area...we will be in a favored zone for seeing clippers
from Thursday through the weekend...so we will likely see at least a
couple of quick hits of light snow over the course of the next week.
After Tuesday...temperatures will moderate...with seasonably cool
conditions expected for the second half of the period.
We will be starting out the period Tuesday morning with the large
high currently dropping out of Canada sitting over central Montana
in the form of about a 1060 mb high. 850 mb temperatures still look to range
between -18c and -22c...so highs in the single digits on Tuesday
still look like a sure bet. Tuesday night...the high will be
centered over the Colorado/Kansas border...but its ridge axis will be
extending due east into the Ohio Valley. This will put US into
return flow...with a steady west-southwest wind expected to blow through the
night...which will really limit our temperature drop. Lows Tuesday night will
likely only be about 5 to 10 degrees colder than the highs Tuesday.
Those west-southwest winds blowing at or above 20 miles per hour will make highs in the teens feel
quite a bit colder on Wednesday...though at least we look to see
plenty of the sun. These west-southwest will also offset the slightly warmer
temperatures expected Tuesday night into Wednesday...sending
apparent temperatures back down below -20c...though current wind
chills Tuesday night are not as cold as what we currently have
tonight. In all likelihood...we will probably end up with a Wind
Chill Advisory for much of the area for a second night in a row.
From Thursday through the weekend...our current 500 mb trough that
extends from basically coast-to-coast will see a chunk of it split
off as a cutoff low that will be over the 4-corners region...while
the bulk of the trough shifts east into eastern Canada. Of importance
for US is the shift of the main upper trough to the east...as that
will bring the baroclinic zone and associated jet our direction.
This pattern will put US in position to see several disturbances
move through. For example...the 29.00 European model (ecmwf) has clippers of various
strength moving across the upper MS valley Thursday night...
Saturday...Monday...and Wednesday. Unfortunately...with subtle
waves such as these this far out...you usually see a bit of variance
between model solutions...and tonight is no different. The only
feature that has decent agreement between at least two models is the
first one...with both the Gem/European model (ecmwf) bringing a 1015 mb low across
central Minnesota...with its attendant swath of light snow impacting mainly
northern Minnesota and northern WI. Given the degree of variability with the
models...the safest course of action to take for probability of precipitation is a blended
forecast...which unfortunately yields what we have...which is
several periods of small snow chances from Thursday on.
As for the 4-corners wave...everything is trending slower and
farther south with that wave. Really...the only true outlier left is
the operational GFS...with the test parallel run of the GFS and the
GFS ensemble mean in line with the rest of the guidance in keeping
that feature way southeast of the mpx County Warning Area.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1121 PM CST sun Dec 28 2014
MVFR conditions will continue for a few sites across far southern
Minnesota for the next few hours...but VFR conditions through the
period for the rest of the area. Current middle level cloudiness will
decrease Monday afternoon.
Kmsp...VFR conditions expected through the period.
/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.
Minnesota...Wind Chill Advisory from midnight tonight to noon CST Tuesday