Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
321 PM CST Thursday Dec 12 2013
Short term...(this evening through friday)
issued at 319 PM CST Thursday Dec 12 2013
Tonight will feature an increase in middle and low level clouds...as
well as increasing chances for light snow /particularly along and
north of Interstate 94/...as a pocket of middle-level frontogenesis
sags into central MN/WI. Although a few sites may dip below zero
tonight...the majority of the forecast area will remain in the
single digits above zero.
Snow chances dip farther south on Friday as the low clouds become
more intrusive. Have included a slight chance of snow
area-wide...although attendant snowfall accumulations would only be
around one half inch or less. Highs on Friday will be hindered
somewhat by the extensive cloud cover...and only expect about a 5-10
degree diurnal rise. Highs should range from 5 above /near
Alexandria/ to the middle/upper teens /Fairmont-Twin Cities-Eau
Long term...(friday night through thursday)
issued at 319 PM CST Thursday Dec 12 2013
Cold weather will continue for the next several days...along with
period of light snowfall. A brief warm up is possible ahead of a
more significant snowstorm which will impact the central Continental U.S.
Towards the end of next week.
Northwest flow will be in place at the start of the period...with a
weak shortwave forecast to dive southeast across northern Minnesota into
northern WI on Saturday. Weak warm air advection ahead of this
wave...as evident by the veering wind profile in the forecast
soundings...should be sufficient to produce light snow across the
region. Increased probability of precipitation to likely category since confidence is high
in light snow falling...despite marginal chances of widespread
accumulation. Accumulations will range from a dusting to less than
in inch. High pressure will build in Saturday night...but another
system will follow quickly on its heels Sunday evening...with a
secondary system on Monday evening. As a result have a long duration
of chance 12hr probability of precipitation in the extended...which will probably be broken
up into smaller windows as the event draws near.
The most intriguing weather of the period falls at the tail
end...when confidence is high that a powerful winter storm will
develop over the Midwest. However the placement of this system
continues to vary greatly...so at this point do not have the
confidence to target any one location. The uncertainty stems from
the fact that this system is highly dependent on the interaction of
a cutoff low that will develop over the next couple of days well
offshore the coast of California. Meanwhile a pv anomaly will dive
southeastward off the coast of British Columbia during the middle of
next week. The Gem/European model (ecmwf) 12.12 phase these two systems about 24hrs
faster than the GFS 12.12. As a result they have a much more
northwestward solution than the GFS...which places the heavy snow
band from Des Moines Iowa through Madison WI. At this time continued
with a consensus blend of the models...but this Thursday/Friday
system will be the one to watch over the next several days.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1230 PM CST Thursday Dec 12 2013
Middle level clouds will be on the increase this afternoon and
evening...with MVFR level ceilings expected to develop late tonight
and Friday morning. Could see some flurries work into the northern
sites /kaxn-kstc/ by 18z Friday...but the main area of light snow
should hold off until Friday eve/night. West/southwest winds will
shift to northeasterly for this evening and Friday. Speeds at or below 10 kts
through the period.
Kmsp...high clouds prevail with an overcast deck circa 6kft arriving
around 00z..then an overcast MVFR deck /2500 feet/ arriving around 18z
Friday. Expect light snow to hold off until after 23z Friday.
/Outlook for kmsp/
Friday night...MVFR ceilings/visibilities with chance -sn. Winds north-northeast 5-10 kts.
Sat...MVFR ceilings/visibilities with a chance of -sn early. Winds north 5kts.
Sun...MVFR ceilings.. MVFR visibilities poss with chance -sn. Winds vrb to southeast
Monday...MVFR ceilings early...otherwise VFR. Winds SW 5-10kts becoming