859
FXUS63 KGRB 181658
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1158 AM CDT Wed Sep 18 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Near-record high temperatures expected to continue today and
  Thursday.

- Locally dense fog is possible across eastern WI early this
  morning and again late tonight into early Thursday.

- Much needed rain associated with non severe thunderstorms are
  expected (50 to 80% chance) in central WI on Thursday night/
  Friday morning.

- A pattern shift is expected this weekend, with highs dropping
  closer to normal Sunday through the middle of next week.
  Confidence on the timing/location and rainfall amounts amounts
  are low early next week.

&&

.DISCUSSION...
Issued at 333 AM CDT Wed Sep 18 2024

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

Summer-like conditions continue into Thursday. Only weather
concerns will be fog trends early this morning and again
tonight/early Thursday, how warm we get and the arrival of
shower/storm chances on Thursday.

Fog Trends:

Light southeast winds, clear skies, a low-level inversion and a
little extra moisture from Lake Michigan has led to some fog
development across mainly eastern WI. Satellite and webcams
showing mainly patchy ground fog so far, but may need a SPS if the
fog continues to expand. Similar set up for tonight into early
Thursday, so will continue/increase fog coverage across much of
eastern WI, with some dense fog possible, especially inland of the
bay/lake. A little more wind just off of the surface across
central and north central WI looks to keep fog chances lower, but
some patchy ground fog will be possible.

Temperatures / Humidity:

Will lean toward the warmer/better guidance today (NBM/CMCnhBC)
keeping highs in the low to mid 80s for most locations, with
mainly 70s near Lake Michigan. Highs on Thursday look to be close
or just slightly cooler than today. Record highs look to be safe
as most are in the upper 80s to low 90s. Dewpoints look to stay in
the upper 40s and 50s for most of the area, with some near 60
closer to Lake Michigan, keeping the heat index near the actual
temp. That said, the area will remain in the "yellow" category
for the HeatRisk...which indicates a "Minor" level of heat-induced
impacts. This level of heat affects primary those individuals
extremely sensitive to heat, especially when outdoors without
effective cooling and/or adequate hydration.

With the clear skies, lows dipped into the upper 40s and 50s
across much of the area early this morning. Looking pretty
similar for tonight, but with a few more upper clouds and some
fog, should keep most lows in the 50s to around 60.

Shower/Storm Chances:

Dry conditions will prevail today and tonight as weak high
pressure pushes across the Great Lakes. On Thursday, a vertically
stacked low pressure system will slowly move from western ND into
southern Canada, with a cold front and shortwave advancing toward
the region during the day. Looking like the majority of the
activity will stay to our west during the daylight hours, but a
stray shower or storm will possible across central or north
central WI Thursday afternoon.

Long Term...Thursday Night Through Tuesday

The big story during this period will be the chance for much
needed rain across the area Thursday night into Friday. Rainfall
amounts at Green Bay, Wausau and Rhinelander are running between
0.20 and 0.40 inches for the month through the 18th (expected to
be dry again today).

500mb ridging across the western Great Lakes will flatten by the
weekend, resulting in temperatures returning closer to normal
Sunday into the middle of next week. On Thursday night, the upper
level disturbance and weak surface cold front will move into and
across the area. Showers and thunderstorms will develop along the
cold front Thursday afternoon across Minnesota and western
Wisconsin and then move east into the area during the evening and
overnight. Based on bufkit soundings, the activity should weaken
some as the evening progresses as the storms move into our area.
Some dry air aloft will also inhibit the potential for stronger
storms. On Friday, the boundary pushes into far eastern Wisconsin.
The combination of daytime heating and increasing CAPE values
could support for a strong storm or two if the boundary is still
lurking across eastern Wisconsin. For Friday night, models have
caught onto a dry forecast which the models began this trend
yesterday. A weak impulse could bring a shower or two to the area
on Saturday. Beyond Saturday, the details of the forecast become
muddled thus confidence is low in the chances of rain on Sunday
through Tuesday. The warmest weather will continue into Friday,
then temperatures will return closer to normal and most likely
will remain at or slightly above normal for the first half of
next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1158 AM CDT Wed Sep 18 2024

Good flying conditions remain expected through the taf period,
except for ground fog late tonight into Thursday morning.

Scattered high clouds will push in from the west at times through
the end of the taf period. These clouds shouldn`t be sufficiently
thick to impact temps. Therefore, mostly clear skies, light
onshore, southeast winds and a low- level inversion will lead to
more fog late tonight into Thursday morning. Models favor areas
over far northeast WI west of Marinette and Oconto, and also
lakeshore areas south of Sturgeon Bay for the highest
probabilities of dense fog.

The fog should burn off from 8 to 9 am on Thursday. Scattered VFR
convective clouds should develop by late morning over central to
north-central WI.

&&

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

&&

$$

DISCUSSION.....Bersch/Eckberg
AVIATION.......MPC