891
FXUS63 KGRB 251832
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
132 PM CDT Wed Sep 25 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Patchy fog may impact the early morning commute today, with
  areas of fog expected late tonight into early Thursday morning.

- Warm temperatures to prevail through the end of the work week,
  with highs running between 10 to 15 degrees above average.

- Slight chance (10-15%) for rain showers Sunday south of highway
  10, otherwise the next chance for rain comes Monday afternoon
  into Tuesday.

&&

.DISCUSSION...
Issued at 354 AM CDT Wed Sep 25 2024

Short Term...Today...Tonight...and Thursday

Precipitation associated with an upper deformation zone remained
well east of the region early this morning. Most locations had
clear skies, though low clouds coming off the bay were affecting
Door and Kewaunee counties, and some low stratus accompanied fog
over north central WI. Mid-level clouds just west of the forecast
area were associated with an upper trough axis and the remnants of
a weak front.

Any lingering fog should mix out by 14z, followed by scattered
cumulus development in the late morning and afternoon due to
daytime heating and the passage of the previously-mentioned weak
front/trough. High temperatures should reach the middle 70s in
most places.

Clear skies, light winds and a weak surface ridge will lead to
fog formation tonight. Conditions should be more favorable than
this morning, as boundary layer winds will be around 5 knots
regionwide. Areas of fog and patchy dense fog look like a good
bet, especially west of the Fox Valley/lakeshore areas. Lows will
be in the 40s and lower 50s, except 50s across Door County.

After the morning fog mixes out, plenty of sunshine is expected on
Thursday. Light south to southwest winds will bring slightly
warmer air into the region, leading to high temperatures in the
upper 70s and lower 80s. Developing onshore flow near Lake
Michigan will keep highs in the lower 70s.

Long Term...Thursday Night Through Tuesday

Models have been trending toward a drier extended forecast over the
past 24-hours. This is thanks in large part to the tropical moisture
from what will be the remnants of Hurricane Helene being shunted off
to the south by a much drier continental air mass.

Precipitation...With a rex block set up across the eastern CONUS to
end the week anticipate dry conditions Friday into the start of the
weekend across the region. The rex block is expected to starting
breaking down this weekend as a ridge moving over the eastern Great
Lakes flattens. At the same time the remnants of Helene will be
advecting north into the Ohio Valley. As moisture from Helene advects
around the norther side of the low Saturday and Sunday there will be
a slight chance (10-15%) for a few showers south of highway 10,
however, with a dry continental air mass forecast to reside over the
wester Great Lakes this weekend the better chances for precipitation
will be shunted to the south. Next chance for precipitation is
forecast to arrive during the early to middle part of next week as
an upper trough and associated cold front move across the region.
Forecast soundings don`t show much if any instability during this
time which limits any severe weather potential, however, with
relatively steep mid-level lapse rates ~ 6.5-7.0C/km there may be a
few flashed of lightning and rumbles of thunder.

Temperatures... With anomalously warm 850mb temperatures ~ 14-16C
more summer like temperatures will persist through this weekend with
highs in the middle to upper 70s expected at most locations. Height
falls and the passage of a cold front Monday into Tuesday does look
to bring seasonal to slightly below normal temperatures back to the
region for the middle part of next week. LREF probs show a 40-50%
chance for highs in the 50s next Wednesday which, except for a few
locations in far northern WI, would be the first day to fail at
reaching 60 degrees since May. Wednesday morning lows also look to
be chilly with possible widespread frost across much of the
Northwoods, and several spots potentially falling below freezing.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 131 PM CDT Wed Sep 25 2024

Scattered cloud cover around 5000 feet will stream across the
region this afternoon and into the evening before dissipating
tonight. Ground fog will be the main concern for tonight, as
cooler temperatures and clear skies allow fairly widespread fog.
The best chance for fog will be across north-central Wisconsin and
near the Lake Michigan shoreline, so the lowest visibility
forecast was included for these areas.

Wednesday will see good visibility and flying conditions returns
after sunrise.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/GK
AVIATION.......Uhlmann