545
FXUS63 KGRB 182332
AFDGRB

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

Updated aviation portion for 00Z 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 00Z TAF Issuance
Issued at 631 PM CDT Fri Jul 18 2025

No significant changes to the previous forecast, just shifted
hours slightly late tonight into Saturday morning.

In general, a wave of low pressure will be tracking along a weak
cold front and across the region from late tonight through
Saturday morning. The low will bring an influx of moisture and
instability, which will lead to a lowering of cloud bases to
IFR/MVFR. Model show probabilities of IFR conditions will be
greater than 50% north of a Merrill (KRRL) to Iron Mountain line
(KIMT) from about 13z thru 18z Sat. However, scattered rain
showers and thunderstorms could will likely impact the area after
09z Sat which could bring down vsbys/ceilings to IFR prior to that
time frame, particularly over north-central and central WI.

The shower activity will mostly depart by late Sat morning or
early afternoon. Then improving flight conditions should take
place for the rest of Sat afternoon.

&&

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

&&

$$

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