229
FXUS63 KGRB 052354
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
654 PM CDT Sat Jul 5 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Scattered thunderstorms this afternoon and evening across the
  region. Isolated severe storms are possible that could produce
  damaging wind gusts. Torrential rainfall is also possible that
  could produce localized urban and low-lying flooding. The most
  favored time frame for strong storms is through 9 pm.

- Until storms arrive later today, it will remain very warm and
  humid with heat indices in the lower to middle 90s over east-
  central to northeast Wisconsin. Those with outdoor plans should
  take precautions for the heat.

- Gusty winds and high waves will lead to conditions hazardous to
  small craft through tonight on the Lake Michigan nearshore
  waters. Small craft should exercise caution on the Bay of Green
  Bay. Hazardous swimming conditions will also be present for the
  Lake Michigan beaches across Door, Kewaunee, and Manitowoc
  counties through tonight.

&&

.DISCUSSION...
Issued at 230 PM CDT Sat Jul 5 2025

Short Term...Tonight and Sunday

Shortwave trough crosses upper Great Lakes through tonight,
dragging a sfc cold front across the state late this evening
through the overnight hours. Strongest wave within the trough is
remnant MCV that is shifting over western Upper Michigan with tail
end of the MCV helping to kick off convection over northwest into
central and north-central WI. Though SBCAPEs have increased to
1500-2500J/kg, stronger effective shear over 30 kts staying ahead
of MCV to the north has limited storm organization thus far over
our area. However, still a risk of isolated severe storms rest of
the afternoon and into the evening given the instability and
solar insolation that has occurred so far today, especially over
east-entral and far northeast WI. PWATs near 2" with slower
effective storm motions will result in brief torrential downpours.
Where individual cells train, there will be a risk of isolated
flooding, especially if the heavy rain occurs in low-lying and
poor drainage areas. Ahead of the storms, heat index values will
remain in the mid to upper 90s, maximized across portions of the
Fox Valley and just to the west. Showers and storms will end late
evening and overnight as winds turn north.

Lingering clouds will partially clear out late tonight into Sunday
morning. Not near as warm and turning less humid behind the front.
Highs reaching the mid 70s to lower 80s, warmest across portions
of central WI. Will be a bit breezy behind the front along the Lake
Michigan shore, but winds and waves look to come up short to justify
the need for additional beach hazard statements. Those heading out
on the water should still expect choppy conditions.

Long Term...Sunday Night Through Saturday

Relatively seasonal weather can be expected during the upcoming
week. Low amplitude, zonal flow will be present across the US-
Canadian border which will send shortwave impulses across the
region on Monday night/Tuesday and also towards Friday. These
will be the time frames of higher shower and thunderstorm
chances. The potential for severe weather appears low at this
time. There are some hints that shortwave troughs crossing during
these times could be stronger. If that is the case and they time
out during peak heating, then severe weather chances would
increase.

Seasonable temperatures are forecast next week. Highs on most
days will range from the upper 70s to middle 80s. Lows each
night will range from the middle 50s to middle 60s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 654 PM CDT Sat Jul 5 2025

Scattered showers and isolated storms will continue through the
evening hours as a cold front moves across the region. Lightning
and torrential rain will be the main threats from the storms, but
the strongest storms could produce small hail and gusty winds.
Lingering showers and an isolated storm is expected overnight,
especially across eastern WI. Will utilize TEMPO groups for the
best thunder chances this evening, but hold off on any thunder
overnight as thunder chances decrease. Have lowered ceilings this
evening and overnight as majority of models have a period of IFR
clouds. Clouds will stick around into Sunday morning, with
partial clearing through the day. Some daytime cu is possible
where the clearing occurs in the late morning and afternoon.

Southwest to west winds will shift to the north behind the cold
front overnight, then to the north/northeast on Sunday. Gusts to
~20 kts are expected.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until midnight CDT tonight for WIZ022-
040-050.
&&

$$

DISCUSSION.....JLA/MPC
AVIATION.......Bersch