Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
614 PM CST Friday Feb 27 2015
Short term...(this evening through saturday)
issued at 341 PM CST Friday Feb 27 2015
Rap analyzed surface pressure this afternoon indicated the center of
a 1040mb surface high sliding east from Iowa into Illinois...the
vast majority of the upper Midwest under clear skies. This feature
will continue its eastward trend through the period. As it
does...the gradient will begin to tighten in western Minnesota
tonight...and progress eastward through Saturday. This setup lends
a non-diurnal trend in western Minnesota tonight as low temperatures will likely
occur around 06z...then remain steady or slightly warm thanks to
increasing southerly winds. Further east...winds will be
lighter...especially toward Ladysmith, WI. This area is expected to
see the coldest overnight lows tonight thanks to the light winds and
clear skies. Teens below zero are likely if the wind GOES completely
calm there overnight.
With the southerly winds increasing during the day
tomorrow...temperatures will rebound into the upper teens and lower
20s. A system developing near the Great Plains will begin moving
east-northeast...and we'll see increasing cloudiness from the low level
southwestern flow Saturday afternoon.
Long term...(saturday night through friday)
issued at 341 PM CST Friday Feb 27 2015
A fairly significant snow event will occur early in the short
term (sat-sun) from the Central Plains to the lower Great
Lakes...with 4 to 8 inches of snow from Kansas to Northern Ohio. The 12z
European model (ecmwf) and Canadian models contracted today on the northern reach
of this system...with a dry forecast for far southern Minnesota and
adjoining areas of WI this weekend. The GFS remained an outlier with
some light quantitative precipitation forecast across far southern areas of our forecast area. Therefore went
with the European model (ecmwf) and Canadian and removed the small probability of precipitation from our
In the wake of the weekend system to our south...high pressure
will move over the upper Mississippi Valley for Monday. The fair
weather will be short lived as yet another low pressure system is
prognosticated to move from the Central Plains to the lower Great Lakes
from Monday night through Tuesday night.
Model trends today indicate that although the GFS and European model (ecmwf)
solutions have basically the same surface low track...the GFS is
too fast. The GFS has the surface low near Chicago by Tuesday
evening while the European model (ecmwf) is back in northern MO. The overnight gefs
solution split the difference with the low in west central Illinois.
Deep/dt on the deterministic GFS shows a slowing trend. The track of
the low is a bit too far south for significant snow in the Twin
Cities. Gefs probabilities for a third of an inch of quantitative precipitation forecast in 12
hours (during the day tue) is 50 percent or higher along and south
of a line from Fairmont to Eau Claire probabilities diminish to
10-20 percent back in the Twin Cities. The location of the higher
probabilities of a third of an inch from the gefs (50 percent +)
is very similar to where the European model (ecmwf) 0.25 inch quantitative precipitation forecast is for Tuesday.
The outlier in all of this today was the Canadian model which
brought much higher amounts of quantitative precipitation forecast (0.25-0.50) across the forecast
area. Deep/dt on the Canadian model showed that it opened up the
closed 500mb low in south central Canada on Tuesday which allows
for much more southern stream interaction. The GFS and European model (ecmwf)
continued with a closed 500mb low in south central Canada with the
ecwmf actually showing a slight southward trend. This certainly
contributed to the lower amounts of quantitative precipitation forecast from the European model (ecmwf) today over
that of the 00z solution. A check of the cips analogs shows a mean
snowfall of 3 to 4 inches from Fairmont to Eau Claire on southward
with less than 2 inches to the north and west of the Twin Cities.
Stayed tuned as things can certainly change as we are three days
out. Needless to say...even with only small amounts of snow...the
Tuesday morning/evening commutes in the Twin Cities could be very
High pressure will then build in for Wednesday and Thursday. It
will be another very cold period with lows Wednesday morning near
zero and in the single digits below zero Thursday morning. Highs
Wednesday will only be in the single digits above zero with highs
Thursday in the teens. Moderation sets in for the end of the week
with highs approaching the freezing mark for Friday.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 601 PM CST Friday Feb 27 2015
High confidence of VFR in the short term with light winds. The
chance for MVFR ceilings increases near the very end of the taf
High confidence in VFR tonight and through the day tomorrow.
Winds will slowly veer to the south with time. Low clouds will be
on the increase tomorrow evening/night.
/Outlook for kmsp/
sun...MVFR possible early. Winds west at 10 kts.
Monday...VFR with MVFR/IFR snow likely late. Winds southeast at 10kts.
Tuesday...MVFR/IFR likely with -sn possible. Winds SW 10kts turning northwest.