541
FXUS63 KGRB 201055
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
555 AM CDT Sun Jul 20 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Dry weather will persist through Tuesday morning. Smoke from the
  Canadian wildfires is expected to reach the surface at times
  today and Monday.

- An active pattern will setup from Tuesday through Thursday,
  with periodic chances of showers and thunderstorms. Strong
  storms and heavy rain will be possible at times.

- Temperatures and humidity rise through the midweek. Highs in the
  90s and heat index values near 100 degrees are most likely on
  Wednesday.

&&

.DISCUSSION...
Issued at 452 AM CDT Sun Jul 20 2025

Short Term...Today...Tonight...and Monday

High pressure will bring dry conditions and light winds to the
region for the second half of the weekend and into the early part
of next week. The main concern will be focused on the smoke from
the Canadian wildfires that is expected to overspread the area
from north to south today and linger into Monday morning. The
initial surge of smoke will be aloft, the smoke is expected to
eventually reach the surface across northern Wisconsin mid-morning
and across the rest of the area by the afternoon. The smoke is
expected to last through tonight and eventually push west of the
area by late Monday morning as winds turn easterly. The smoke may
linger across far north-central Wisconsin into Monday afternoon.

Highs are expected to generally be in the upper 70s today and
Monday, with lows in the 50s tonight.

Long Term...Monday Night Through Saturday

Precipitation...Weather will likely remain dry through Tuesday
morning, then it`s the start of an active pattern Tuesday
afternoon as northeast Wisconsin resides near the northern part of
an upper ridge, with several embedded shortwaves tracking towards
the area throughout the midweek. This coincides with a slow
moving frontal system approaching from the west, an open Gulf, and
a strong low level jet feeding in plenty of moisture, as noted by
increasing dew points and PWats, particularly by Wednesday and
Thursday. Tds peak in the low to mid 70s both days, with Pwats
generally in the 1.7 to 2.0 inch range, sometimes getting as high
as 2.2 inches, which reaches the climatological max.

As previously noted, timing for rain and thunderstorms is
difficult to pin down, but there will likely be a few rounds of
thunderstorms or a thunderstorm complex. There is some agreement
that a shortwave moves through the northern Plains and across
northwest Wisconsin Tuesday afternoon and evening. CAPES build to
1-2k J/kg by the afternoon, but there is a cap to overcome
initially, and initiation may be more likely farther west, with
perhaps just waning storms getting into this area later in evening
or overnight.

Wednesday and Thursday remain the more interesting days as the
surface cold front slowly approaches and moves through the state.
There is once again a cap to overcome, but 2-4k J/kg of CAPE
otherwise. Deep shear and lapse rates are fairly modest, but given
the high CAPE the potential for severe storms exists, along with
heavy rainfall and localized flooding to due the high
moisture/pwats and possibility for training or slow-moving storms.

The surface cold front pushes through Thursday night, which will
bring drier conditions to the north Friday through the weekend.
This boundary stalls out just south of Wisconsin, which keeps a
low to medium rain and thunderstorm chance across the southern
CWA, generally south of highway 29, though the weekend.

With all that said, there will be plenty of precip-free periods
as well, and not all locations will receive every round of
rain/storms.

Temperatures...Of higher certainty is the temperatures and
humidity, particularly on Wednesday. NBM probabilities show a
50-75% chance of highs at or above 90 degrees for all but north-
central WI/Northwoods area, with dew points in the middle 70s.
This will create heat index values near 100 degrees. Temps and dew
points are slightly lower Thursday, with a 20-40% chance of
reaching 90 degrees for the same area (central into northeast and
east-central WI), but it will still feel rather humid. Heat
headlines may eventually by needed.

After the front comes through, temperatures will still trend above
normal from Friday through next weekend, but it will not feel
like oppressive humidity due to slightly lower dew points in the
60s.

KLJ.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 555 AM CDT Sun Jul 20 2025

Shallow patchy fog this morning should dissipate quickly after TAF
issuance. At this time it does not look to impact the TAF sites.
Skies should turn partly cloudy today with areas of smoke
developing during afternoon and continuing overnight. Continued
with the FU mention in this set of TAFs.

KOSH - A BKN deck of clouds around 4k ft should give way to mostly
clear skies later this morning. Elevated smoke will likely move
into the region after 15z. It`s possible that the smoke could
reach the surface at times this afternoon and tonight, but
confidence is relatively low.

&&

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

&&

$$

DISCUSSION.....Kurimski/KLJ
AVIATION.......Kurimski