Area Forecast Discussion

FXUS63 KGRB 142351
Area Forecast Discussion
National Weather Service Green Bay WI
551 PM CST Fri Dec 14 2018
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Saturday
Issued at 230 PM CST Fri Dec 14 2018
High pressure conditions are expected to dominate the short term
period as the upper level ridge settles into place. Skies will
remain clear into the evening hours, under a large area of
The overnight hours will bring another round of fog challenges.
A strong low level inversion coupled with little to no winds 
through the lower levels will allow for fog formation tonight. 
Moisture profiles are considerably more shallow this evening than 
the past couple nights, which will help limit dense fog and low 
stratus formation, but neither can be ruled out. Left some hints
of scattered low clouds in the forecast along with patchy fog. If
low stratus doesn't form, skies will clear aside from the fog,
which will heavily impact temperatures. Typical cool spots could
be several degrees warmer or cooler depending on the sky cover
After sunrise tomorrow, skies will rapidly clear out again for a
sunny start to the day as high pressure and subsidence remain in
the region.
Stayed close to guidance for daytime temperatures Saturday.
Dropped the temperatures a couple degrees in the northern
Wisconsin cool spots given the uncertainty for overnight sky
.LONG TERM...Saturday Night Through Friday
Issued at 230 PM CST Fri Dec 14 2018
The mean flow across the CONUS to remain progressive and split
well into next week. One southern stream system exits the eastern
CONUS late this weekend, with the next system of interest to enter
the western CONUS Sunday/Sunday night. Ahead of this system, a
downstream upper ridge to reside over the central CONUS with a
northwest flow into WI. Weather is expected to remain quiet and
mild through Tuesday before the western CONUS system arrives over
the Great Lakes and brings our next chance for precipitation
Wednesday into Thursday. Temperatures to remain above normal
through the end of next week.
The current surface ridge and weakening upper ridge will get
pushed south Saturday night as a cold front and shortwave trough
enter the western Great Lakes after midnight. Lack of moisture and
mid-level forcing will preclude the mention of any precipitation,
with only a minor increase in high clouds anticipated. Cannot rule
out some patchy fog during the night as winds are still light and
variable, but the fog should not be nearly as widespread as
previous nights. Most locations should see min temperatures in the
lower to middle 20s. The cold front/shortwave trough combination
sweep across the rest of WI Sunday morning with little more than a
few clouds and a wind shift to the west. Dry conditions remain
intact with max temperatures in the 35-40 degree range.
Upper ridging over the Plains and a surface ridge that stretches
from east of Lake Winnipeg through the Midwest to the southern
Plains, will bring a northwest flow into WI Sunday night. More
clouds are expected across northern WI due to lake effect, however
no snow is forecast as temperatures aloft are not that cold. More
wind in the forecast will also eliminate any mention of fog. Min
temperatures to range from the lower 20s central WI, to the upper
20s along Lake MI. The surface ridge axis edges closer, reaching
the Upper Midwest on Monday. While skies are forecast to be partly
cloudy, the prevailing northwest winds will chop 5 to 10 degrees
from temperatures compared to Sunday. While readings will be in
the upper 20s to around 30 degrees central WI, lower 30s for
eastern WI, these values are still a few degrees above normal for
This surface ridge slides across WI Monday night and already
reside just to our east by daybreak. Mostly clear skies to partly
cloudy skies and light winds should bring a cold night to the
region with most locations in the teens. By Tuesday, the surface
ridge shifts toward the eastern Great Lakes, while the trailing
upper ridge reaches the western Great Lakes. A return flow into WI
will bring the onset of WAA into the area, but the cold start to
the day is forecast to limit max temperatures to around 30 degrees
north, lower 30s south.
Attention turns toward the Canadian Prairie/northern Rockies where
a Pacific system to be located Tuesday night. This system to
quickly move east-southeast through the northern Plains into the
Upper MS Valley on Wednesday. There appears to be enough moisture
available to interact with the WAA to at least bring a chance of
precipitation to northeast WI on Wednesday. Max temperatures 
generally in the middle to upper 30s will likely lead to a 
rain/snow mix of some kind where precipitation does occur. 
The CMC/ECMWF still digs an upper trough over east-central NOAM
sooner than the GFS, thus a slower eastward movement which would
impact both precipitation amounts and timing of the associated
cold front's passage. May need to raise pops a bit from the
previous forecast with a chance for light snow Wednesday night.
Too many questions yet to surmise possible accumulations, but it
looks minimal right now. The entire system gradually move to the
east on Thursday with most of the precipitation chances ending by
the afternoon. The exception would be north-central WI where
northwest winds and CAA could bring lake effect snow showers into
that part of the region. Not much diurnal warming anticipated on
Thursday with max temperatures in the lower to middle 30s.
The chance for lake effect snows will continue through Thursday
night before the approach of another surface ridge would end the
lake effect threat on Friday. The rest of the region should see
mostly cloudy skies Thursday night with perhaps a little sunshine
for Friday. Temperatures are still forecast to be about 5 degrees
above normal on Friday, although there are hints of colder air
reaching WI next weekend.
.AVIATION...for 00Z TAF Issuance
Issued at 551 PM CST Fri Dec 14 2018
Big question for tonight through early Saturday is whether or
not fog will form. The fog should hold off through most of the 
evening hours but there should be some beginning after midnight 
where winds become calm and there is snow on the ground. 
Visibilities could drop below minimums for awhile late tonight 
through 15z Saturday in some places. 
Whatever fog does form should dissipate by midday Saturday with
good flying weather Saturday afternoon and evening. Fog could form
again late Saturday night but seems less likely than tonight.
SHORT TERM.....Uhlmann
LONG TERM......Kallas