Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Green Bay WI
1029 PM CST Wednesday Jan 28 2015

Updated aviation portion for 06z taf issuance

issued at 858 PM CST Wednesday Jan 28 2015

Kdlh and kmpx radars showing classic dz/fzdz signature. That is
also beginning to appear on the karx radar as well. Wish
confidence were higher...but have seen enough to justify going
with a freezing rain.Y for the entire forecast area /timing in coding below/.
Roads could be very slick for the morning commute...even if the
fzdz is winding down in the west by then. Precipitation may also change to snow
for a couple hours tomorrow morning. That would make for especially
slick roads if it falls on ice from the fzdz. Perhaps a ww.Y would
be a little better...but for simplicity sake with keep with the
freezing rain.Y that offices to the west already have running.

Updated product suite out as soon as possible.

Coordinate west mkx.

issued at 459 PM CST Wednesday Jan 28 2015

Model forecast soundings look pretty favorable for fzdz when ascent
increases in the late evening. But just not sure how much precipitation will
occur. Nothing noted on nearby surface observation now...though some fzdz
likely occurring back in eastern ND. Middle-level returns also increasing some
on kdlh radar...which may indicate a little more potential for
seeding with ice crystals than the forecast soundings would suggest.
Will continue to monitor the sitn this evening...and am prepared to
issue a headline if/when it becomes apparent that a sufficent
amnts of precipitation will fall as fzdz. Will continue to handle with Special Weather Statement until
that point.

Short term...tonight and Thursday
issued at 232 PM CST Wednesday Jan 28 2015

Plenty to deal with over the next 12 to 18 hours as a modest
system moves across the region and brings the potential for a
mixed precipitation event to NE WI. Main forecast issue are trying to determine
the precipitation type and then extent of any icing that would warrant a

The 20z msas surface analysis indicated a pair of weak low pressure areas
over the northern plains connected by a cold front that extended southward into
the Southern Plains. Hi pressure was situated over the eastern Great Lakes. A
broad southerly wind between these systems brought mild air into
WI with above normal readings for late January. Vsbl satellite imagery
showed plenty of middle/hi clouds over NE WI as the low clouds from
this morning had mainly dissipated.

After a quiet start to the night...forecast to become quite complicated
from late evening forward as the surface cold front/mid-level shortwave
trough push across WI. The big problem is a lack of saturation in
the mid-levels...thus a lack of ice being introduced and leading
to supercooled water drops reaching toward the surface. There is also
a dry wedge of air forecast by the models around 7h that has to be
overcome. Based on the new data...expect to see freezing drizzle
being the primary forecast type before gradually changing over to all
snow late tonight behind the cold front as cold air advection takes over. Not confident
enough about quantitative precipitation forecast amounts to issue a headline at this time...thus will
issue a Special Weather Statement stating the potential for slick roads for the morning
commute. Temperatures should not drop off much tonight as warm air advection continues to push
into WI ahead of the cold front. Look for mins to mainly be in the middle
to upper 20s.

Freezing drizzle/light snow to linger into Thursday morning until the
shortwave trough departs the area. The bigger concern for Thursday will be
the lake effect potential across north-central WI as cold air advection sends 800 mb temperatures
down to almost -20c over Western Lake Superior and trajs become
favorable. The only real negative looks to be a low-level
inversion which would limit snow accumulations. Have raised probability of precipitation
to likely for northwest sections of Vilas County...but kept accumulations
less than an inch for now. Maximum temperatures to still be reasonably mild
(mainly due to the warm start to the day) with readings in the upper
20s north...middle 30s E-cntrl. These maximum temperatures could top out around
midday before slowly falling in the afternoon as the colder air
settles in over the region.

Long term...Thursday night through Wednesday
issued at 232 PM CST Wednesday Jan 28 2015

Lake effect snow showers are likely across north central WI
Thursday night...with Delta T/S around 20...favorable north-northwest
trajectories...and low level moisture in place. Raised probability of precipitation over
far north central WI and increased snow totals slightly...however
accumulations should remain under an inch for most locations. Any
lake effect activity will diminish Friday morning as winds become
more westerly...keeping any snow showers over Upper Michigan.
Otherwise...dry conditions are expected Thursday night and Friday
as high pressure slides over the region.

A weak clipper system will push across the northern Great Lakes
Friday night...however most of the snow should stay north of
state...closer to the main shortwave energy. However...cannot rule
out some flurries across much of the will mention a
small chance of light snow across the area...with little to no
accumulations. Winds become northwest behind the clipper...triggering
another shot at lake effect snow Saturday night into Sunday.

Attention then turns to the system for the weekend. It was looking
like a good chance for some kind of storm to develop/move across
the Ohio Valley and bring accumulating south to at least southern
WI Saturday night into Sunday. 12z European model (ecmwf) completely jumped ship and
now shows a more progressive system with little to no snow for WI.
This idea is supported by the GFS...although it brings some light
snow to the southern half of WI. Gem is still on board with a more
wrapped up system and deeper upper trough digging across the Ohio
Valley. This would bring more significant snowfall to the state...
and linger the snow into Monday morning. Will let the models try
to get on the same Page...and continue with chance probability of precipitation across
the southern half of the County Warning Area...closer to whatever system
materializes...and confine the probability of precipitation to Sunday. Some lake effect
activity is again possible late in the weekend and into next week.
Otherwise...dry conditions are expected as high pressure builds
in. Next chance for precipitation will be late Monday into Tuesday as a
weak system crosses the Great Lakes.

Saturday looks to be the warmest day of the much
colder air will be ushered into the region behind the systems on
Sunday/Monday and next week. Highs on Sunday and Monday will range
from the upper single digits to middle teens...with lows below
zero across central and north central WI Sunday night and Monday

Aviation...for 06z taf issuance
issued at 1028 PM CST Wednesday Jan 28 2015

Ceilings in the west now MVFR...and expect further lowering there as well
as across the east...eventually into the the IFR/LIFR categories. Soundings
look favorable for least until surface trough shifts east of the
area and middle-level moisture increases. Conditions should bounce
back into the MVFR category Thursday in cold air advection regime.

Grb watches/warnings/advisories...
Freezing Rain Advisory until 8 am CST Thursday for wiz013-021-

Freezing Rain Advisory until 6 am CST Thursday for wiz005-


short term.....Kallas
long term......bersch

National Weather Service Glossary of Abbreviations