616
FXUS63 KGRB 060400
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1100 PM CDT Sat Jul 5 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Isolated thunderstorms with torrential rainfall are possible
  overnight which may produce localized urban and low-lying
  flooding.

&&

.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 06Z TAF Issuance
Issued at 1058 PM CDT Sat Jul 5 2025

Showers and isolated storms will continue through the late
evening and overnight hours, especially across eastern WI, as a
cold front moves across the region. Lightning and torrential rain
will be the main threats from the storms. MVFR and possibly IFR
ceilings are expected overnight into Sunday morning, with partial
clearing through the day. Some daytime cu is possible where the
clearing occurs in the late morning and afternoon. If any clearing
occurs overnight, some fog would likely develop.

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

&&

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

&&

$$

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