Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
305 PM CST sun Feb 1 2015
Short term...(this evening through monday)
issued at 305 PM CST sun Feb 1 2015
Snow has exited Minnesota to the southeast as of middle afternoon
with clearing skies now pushing through central Minnesota into far
western Wisconsin. This clearing will continue advancing southeast
through the rest of the afternoon and clear skies are expected
area wide by early to middle evening. Winds will subside and
become light and variable for a time overnight before turning
south early Monday. This should set up ideal radiational cooling
conditions... particularly where several inches of fresh snow
fell over far southern Minnesota. Here...temperatures may drop to 10 below depending
how winds decouple...with zero to 5 below elsewhere where there is
very little snowpack.
Monday looks continued chilly but with a fair amount of sunshine
early. Some middle level clouds return in the afternoon.
Long term...(monday night through sunday)
issued at 305 PM CST sun Feb 1 2015
Large scale pattern evolution...
a cold pattern for US... with eastern troughing and ridge along
the West Coast... will persist through much of the week.
However... by the weekend the Hudson Bay low will be displaced
northward and the upper flow will become more zonal as the western
ridge flattens and shifts a bit eastward.
Forecast item/S/ of concern...
there remain two main chances for some light snow... on Tuesday
and again late Friday and Saturday.
the guidance is in good agreement on the overall large scale
pattern through the week... and transition to more of a zonal flow
over the weekend. There remain some differences in the track of
the Tuesday system... although the guidance has tightened up quite
a bit with the European model (ecmwf) and GFS compromising from where they were
yesterday. The differences with the late week/weekend system are
more significant at this time. Given the ensemble spread and run
to run variations... there/S no reason to latch onto any specific
solution at this point... so will continue to utilize a consensus
approach and have high chance probability of precipitation over a somewhat longer period
than what will likely be needed as the event draws nearer.
Sensible weather expectations...
a weak surface trough will move through tomorrow night and early
Tuesday... but with minimal moisture in place there doesn/T look
to be any chance of precipitation. A weak and sheared out shortwave will
drop southeast through the region on Tuesday... with a period of
some weak warm advection and middle-level frontogenesis. This
currently looks to bring light snow... with accumulations of
around an inch or so... to mainly the western and southern portion
of the forecast area... particularly from the Minnesota valley
southward. Some flurries could linger into Wednesday as strong
cold advection and decent low level lapse rates work into the area
behind the Tuesday feature. High pressure will then keep things
cold and dry into Friday. Good return flow and warm advection will
setup Thursday night into Friday... but the profile doesn/T look
to become saturated until things are north of our area... with the
main chances for any precipitation on Friday/Friday night looking to be
mostly off to our northeast. The baroclinic zone will hang up in
our vicinity Friday night through Saturday night... and where it
loiters will factor into where the best snow chances are from
Saturday into early Sunday as a shortwave and weak surface low
drop through the area. Regardless... forcing is not particularly
impressive... so wouldn/T appear to be a significant event in any
Detailed discussion for item/S/ of concern...
significant precipitation is not expected with either the Tuesday or
weekend system... although somewhat higher amounts would be
possible with the weekend system given better moisture
availability. However... at this point neither feature appears
there is high confidence in the occurrence of below normal
temperatures for much of the week... with a warming trend toward
the end of the forecast period. There is moderate confidence in a
light snow event across mainly the west and south on Tuesday...
and in a second light snow event Saturday into early Sunday...
although the location of that is still in doubt.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1230 PM CST sun Feb 1 2015
Snow has tapered off at all the taf sites...with VFR conditions
expected for the rest of the period. Northeast winds will ease
later this afternoon...become light and variable tonight...then
Kmsp...VFR expected. North northeast winds will back north and
ease this evening before becoming south Monday morning.
/Outlook for kmsp/
Tuesday...chance MVFR/-sn. Wind west 5 knots.
Wednesday...VFR. Wind northwest 10-15 knots.