Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
215 PM CST sun Dec 28 2014
Forecast discussion for routine afternoon forecast issuance
Short term...tonight and Monday
issued at 208 PM CST sun Dec 28 2014
Quiet weather through Monday with main concern being clouds tonight
and their effect on low temperatures.
A cold front will sag south through the state tonight...ushering
in noticeable colder temperatures. The front looks like it will
clear the County Warning Area around midnight...so there will be plenty of time
tonight to cool off. Models have a fairly impressive wedge of dry
air moving over Wisconsin after 00z tonight...so think there will
be some clearing tonight mainly in north central Wisconsin. Models
then bring in some high clouds after midnight. Exactly how much
coverage and opaqueness we will get out of these clouds is in
question. Clouds through the afternoon were fewer than advertised
by models...so followed this trend and went with less clouds.
Thus...dropped overnight lows a degree or two in north
central where there will be the most clearing...with many locations
falling below zero. Later shifts may need to adjust lows up or
down though...depending on cloud trends.
Monday will see increasing clouds again as another weak piece of
energy swings through the state and enhances another cold front
dropping south through the day. Much colder air behind this front
as strong cold air advection sets up over the area. This colder air wont really
infiltrate the area until Monday night...but still noticeably
colder Monday than Sunday. Not much change made to the forecast
other than increased high temperatures Monday slightly in eastern
Wisconsin where little to no snow cover was present.
Long term...Monday night through Sunday
issued at 208 PM CST sun Dec 28 2014
No significant changes to previous forecast.
Positively tilted longwave trough over the Continental U.S. Will gradually
evolve to split flow with longwave trough persisting over the
northern Continental U.S. And cutoff low developing over the southwest US by the
middle of the work week. Generally dry and cold for the first half
of the work week with large high pressure system settling over
much of the central Continental U.S.. large area of high pressure will bring
cold airmass over the western Great Lakes with morning lows on
Tuesday 5 to 10 below zero across central and northern Wisconsin.
Morning lows on Wednesday will be even colder...falling into the
10 to 15 degree below zero range. Wind chill values by Wednesday
morning will likely to be in the -15 to -25 degree range west and
north of the Fox Valley.
During the second half of the work week...several weak upper-
level impulses will rapidly drop southeast toward the western
Great Lakes. With Gulf moisture completely cutoff by massive high
pressure over the Southern Plains...will likely only see some
passing middle-level clouds with these weak impulses and perhaps some
flurries or light snow showers across the far north.
Sometime by early next weekend...cutoff over the southwestern US
is forecast to eject northeast into the Southern Plains. Still
considerable spread in various model solutions on when and where
cutoff ejects northeastward...and where subsequent cyclogenesis
over the Southern Plains will occur. Latest European model (ecmwf) is slower and
takes surface low well south of the Great Lakes region...while
GFS/GFS ensemble mean is much faster and further north taking
surface cyclone into the central Great Lakes region. Gem is
somewhere in between. Bottom line is that confidence on evolution
of this system for the upcoming weekend is low. Am inclined to
lean more toward the European model (ecmwf) and northern stream flow dominating the
flow over the western Great Lakes by the weekend and keeping
southern stream system to our south.
Aviation...for 18z taf issuance
issued at 1040 am CST sun Dec 28 2014
Scattered MVFR ceilings possible this this afternoon across
northeast Wisconsin...with a few flurries and reduced visibility in
central Wisconsin through early afternoon. Otherwise VFR weather
expected tonight through Monday morning with light surface winds
veering north this evening.