Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
243 am CST Thursday Mar 5 2015
Forecast discussion for routine morning forecast issuance
Short term...today...tonight...and Friday
issued at 242 am CST Thursday Mar 5 2015
Large frontal boundary extending from Texas to the Tennessee Valley
region to the East Coast continues to slowly sag southeast over
that part of the country today. Swath of winter storm headlines
and flood warnings along and near this intense boundary with warm
Gulf moisture to the south and the Arctic air to the north.
Much quieter but colder regime to dominate northeast Wisconsin today
into tonight as the cold high pressure ridge drifts over the Great
Lakes and upper Midwest.
Cold start this morning with neutral temperature advection will
produce another cold day today under plenty of sunshine.
Challenge tonight will deal with how fast the temperatures will plummet
prior to some increase in clouds with a northern stream short wave
trough dropping in. Forecasts in good agreement with a clear start
followed with increasing clouds...so will focus min temperatures a few
hours after midnight then go the steady Route. Forecasts do not
generate much precipitation but will keep the small precipitation mention of
flurries due to the morning weak warm air advection pattern followed by the
Long term...Friday night through Wednesday
issued at 242 am CST Thursday Mar 5 2015
Mean flow across the Great Lakes to transition from northwest this
weekend to SW by the middle of next week as the eastern Pacific/West
Coast upper ridge weakens. NE WI will have to deal with a couple of weak
systems in the northwest flow this weekend...but any precipitation appears to be
light as moisture availability is marginal at best. As the flow
turns west then SW...Pacific air will replace the Arctic air over
the eastern half of the Continental U.S. With a significant warm-up on the way.
Exactly how warm we can get will be the main issue in the long-term.
How long this warmer air can hang around is open to debate as the
models differ with the handling of a Pacific system across the northwest
Continental U.S./SW Canada. More on this in the coming days. For now...let's
enjoy the March thaw.
The first of these weak systems is forecast to dive southeast into the Great
Lakes after midngt as a clipper low pressure to reach vicinity Lake
Superior by 12z Sat. A cold front will accompany the surface low into the western
Great Lakes...along with modest forcing from a weak middle-level
shortwave trough. There does appear to be enough moisture to squeeze
out a little light snow or flurries across the forecast area...especially
over northern WI where better saturation is shown on the time sections.
Thickening clouds will help to hold temperatures up with mins only dropping
into the teens to around 20 degrees. The clipper heads toward the eastern
Great Lakes on Sat with a very weak hi pressure moving into the Midwest.
Any lingering light snow or flurries should end in the morning with
mostly cloudy skies expected for the rest of the day. A more mild
start to the day will allow maximum temperatures to warm into the 30-35 degree range
over most of the forecast area.
NE WI to reside between systems Sat night as the weak hi pressure shifts
southeast toward the Tennessee Valley and the next system pushes southeast to just east
of Lake Winnipeg by 12z Sunday. Clouds are expected to thicken
during the overnight hours as the surface hi pulls away with min temperatures
generally in the 15 to 20 degree range. This next clipper does not
dive as far southeast as its predecessor...instead tracking more east-southeast
across southern Ontario on Sunday. A cold front/shortwave trough combination
will sweep across NE WI primarily during the afternoon and could
have enough moisture to bring at least a small chance of light snow to
the area. Maximum temperatures are expected to reach the middle to upper 30s (pre-
frontal warming) which may allow a little rain to perhaps mix with
the snow. If this were to happen...it would be south of Highway 29 in
The mean flow across the Continental U.S. To essentially be zonal by next Tuesday
with the active northern branch keeping any systems moving eastward across
southern Canada. This leaves NE WI under the influence of hi pressure over
the Ohio River valley and a prevailing SW wind into the Great
Lakes. Mild Pacific air will continue to overspread WI with maximum temperatures on
Tuesday able to reach the lower to middle 40s north/Lakeshore...middle to upper
Forecast toward the middle of next week becomes more muddled as the
models are struggling with the split flow over the eastern Pacific and
a resultant system moving somewhere along far southern Canada or northern
tier of states. The GFS is much more aggressive with this system
by taking a strong surface low across southern Canada and sending a strong
cold front into WI Wednesday afternoon. Meanwhile...the European model (ecmwf) is much weaker
and farther south with the surface low and essentially sags the much
weaker cold front into northern sections of the Great Lakes on Wednesday. For all
intensive purposes...this major model conflict would not impact NE
WI until after the end of the forecast period and mainly affects
temperatures. Until then...Wednesday should still be a warm day with maximum temperatures
similar to Tuesday.
Aviation...for 06z taf issuance
issued at 1029 PM CST Wednesday Mar 4 2015
Now that winds have settled down...good flight conditions /VFR
category/ are anticipated for the next 24 hours as high pressure
passes SW of the area.