395 
FXUS63 KGRB 061111
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
511 AM CST Wed Dec 6 2023

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Well above normal temps (10-20 degrees), but below records, are
  likely on Friday.

- Low probabilities (10-20%) of significant winter weather
  continue on Saturday and Saturday night over northeast and 
  north-central Wisconsin.

&&

.DISCUSSION...
Issued at 250 AM CST Wed Dec 6 2023

SHORT TERM...Today...Tonight...and Thursday

High pressure over the western Great Lakes will slide east today,
allowing a warm front to lift north over the region. The warm
front will turn winds from a west to northwest direction to a
south to southwest direction by this afternoon. Despite the
passage of a warm front, clouds are expected to remain across the
region with very shallow mixing heights as the warm air advection
will mainly be aloft. Therefore, highs are only expected to rise
into the 30s this afternoon. There will be some weak isentropic
lift associated with the warm front this afternoon; however,
model soundings show quite a bit of dry air in the column. Given
the dry air and weak lift only a few flurries or sprinkles are
possible as the warm front lifts north today. Winds will increase
behind the warm front this afternoon and this evening, with
southwest winds gusting to 25 to 35 mph at times, particularly
across east-central Wisconsin and the lakeshore.

Weak ridging will then slide through the western Great Lakes
region tonight, which is expected to keep the area dry. The ridge
will also cause winds across east-central Wisconsin and the
lakeshore to ease throughout the overnight hours. Although there
be some partial clearing at times tonight, surface winds should
keep temperatures from plummeting too much across the area. Lows
tonight are expected to range from the middle 20s across the
north, with around 30 across east-central Wisconsin and the
lakeshore.

The ridge will slide off to the east on Thursday, allowing surface
winds to once again turn south to southeast throughout the day.
Despite southerly winds, model soundings once again show a steep
low level inversion and shallow mixing height only to around 1000
kt AGL. Therefore, highs on Thursday will be a bit cooler than
expected with a southerly wind as the warm air advection will once
again mainly be aloft. Highs on Thursday are expected to mainly be
in the lower to middle 40s.

LONG TERM...Thursday Night Through Tuesday

Thursday night through Friday night...Low pressure will be traveling 
northeast from North Dakota to northern Ontario during this time 
period.  The airmass south of the low track will be very dry through 
Friday and therefore no precip is expected.  Highs on Friday remain 
expected to range from 10 to 20 degrees above normal.

On Friday night, gulf moisture will be surging north and into the 
region ahead of a developing cyclone.  Forecast soundings indicate 
the chance of drizzle or light showers increasing through the night 
as the gulf moisture arrives.  Thermal profiles suggest most precip 
will consist of liquid, except for far north-central WI where temps 
will be close to freezing.  Little to no accumulations are expected 
by 6 am Saturday.

Saturday through Tuesday...Model differences remain large regarding 
a strengthening cyclone forecast to cross the region Saturday into 
Sunday.  In general, there has been a slight slowing trend of the 
deep trough over the central Plains on Saturday, while the surface 
low track has shifted to the northwest.  The probabilities for 
greater than 0.25 precip has increased over northeast Wisconsin, 
while the probabilities for greater than 2 inches of snow has 
shifted west from northeast to north-central WI, which makes sense 
given the surface low trends.

With that said, however, the GFS seems to be an outlier compared to 
other operational/ensemble model systems.  A positively tilted 
trough would argue for a more progressive, suppressed, and weaker 
cyclone passing across the upper midwest than the GFS depicts.  This 
would favor more of an ECMWF/Canadian solution.

Given the large model spread and large run-to-run changes of the 
operational models, awfully difficult to get a handle on the 
potential for hazardous weather.  The strong dynamics with this 
system would argue for low probabilities (20-30%) of significant 
snow accumulations in the Saturday to Saturday night time period. 
Confidence is low where these hazards will occur however.

Colder air will filter into the region behind the system for early 
next week.  Still indications of clipper energy moving through the 
region at some point early next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 511 AM CST Wed Dec 6 2023

A mix of VFR and MVFR cigs prevailed across the area early this
morning as observations show the MVFR cigs across central and 
north-central WI slowly eroding. Meanwhile, VFR cigs were filling
in across east-central and northeast Wisconsin where clouds had
previously cleared. Overhead some mid to high level clouds were
also noted moving over the TAF sites. Any lower clouds that clear
out this morning should fill back in this afternoon, with bases
expected to be mainly VFR in the afternoon. Low and mid clouds
should then dissipate tonight, leaving only high clouds during the
overnight hours.

Light west winds will turn southwest and increase this afternoon,
with gusts of 15 to 25 kts, as high pressure gradually shifts 
eastward. In addition, a period of LLWS, with westerly winds to 40
kts, is expected late this afternoon into the evening. Winds will
then die down late tonight as a ridge of high pressure moves back
over the region.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Kurimski/MPC
AVIATION.......Kurimski