494
FXUS63 KGRB 190348
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1048 PM CDT Fri Jul 18 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Showers and scattered thunderstorms expected late tonight into
  Saturday, then pleasant conditions return Saturday night through
  Monday. Smoke from Canadian wildfires returns Saturday night
  into Sunday.

- An active pattern is expected during the middle of next week,
  with periodic chances of showers and thunderstorms. Strong
  storms and heavy rain will be possible at times.

&&

.DISCUSSION...
Issued at 346 PM CDT Fri Jul 18 2025

Skies were mostly cloudy over NC WI this afternoon, while partly
cloudy conditions were observed elsewhere. A short-wave was
tracking through far northern WI, bringing a few light sprinkles
or virga to areas near the U.P. border. Temperatures were
seasonably cool; ranging from the upper 60s far north and near
Lake Michigan to the lower to middle 70s elsewhere.

Expect mainly dry conditions to prevail this evening. H8 WAA
developing ahead of an approaching cold front, and upper forcing
from a weak short-wave or jet streak, should generate showers and
scattered thunderstorms late tonight, mainly west of the Fox
Valley/lakeshore areas. MUCAPE (all elevated) is only expected to
be 300-700 j/kg, so severe weather is not expected. The cold
front will track southeast through the forecast area on Saturday,
with showers and embedded storms continuing until it shifts south
of the region late in the day. Think there may be enough cloud
cover and showers around to limit the severe threat, but CAPE of
1000-1500 j/kg across C/EC WI bears watching, as suggested by the
small sliver of a Marginal severe risk seen on the SPC Day 2
Outlook.

High pressure brings dry and pleasant conditions Saturday night
through Monday. Smoke from Canadian wildfires will push into
the forecast area Saturday night into Sunday. While the initial
surge should be aloft, there is some potential for surface-based
smoke on Sunday. As such, have increased sky cover a bit Saturday
night, and added patchy smoke to the forecast on Sunday.

Zonal flow sets up across the region for the rest of the work
week, with very warm and more humid conditions returning to the
forecast area. Timing and location of individual disturbances
(possibly convectively-induced MCVs) will be very difficult, so
specific details on pops will be initially lacking. There is some
consensus that a couple rounds of convection could develop as a
warm front lifts toward the region Tuesday into Tuesday night,
followed by a cold frontal passage sometime during the Wednesday
to Thursday time frame. During this mid-week period, CAPE is
expected to increase to 2-3K j/kg, so a period or two of severe
storms could occur. In addition, with PWATs increasing to around 2
inches and surface dew points rising into the middle 60s to
middle 70s, heavy rainfall will also be a distinct possibility.
Look for highs to reach well into the 80s, and heat indices could
get as high as the upper 80s to lower 90s in parts of C/EC WI.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1048 PM CDT Fri Jul 18 2025

The biggest change in the 06z TAFS was to delay the clearing trend
on Saturday afternoon as cyclonic flow and lingering low level
moisture should keep MVFR stratus across the area longer than the
previous forecast indicated.

Otherwise, the forecast is generally on track. Low pressure
remains expected to bring IFR/MVFR ceilings/visibilities and
scattered showers and thunderstorms late tonight through Sat
morning. Confidence is relatively low regarding the coverage of
thunderstorms and focused on central and east-central WI where the
greatest instability will be. Think the rain threat will end early
in the afternoon.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......MPC