761
FXUS63 KGRB 010855
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
355 AM CDT Tue Jul 1 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Dry weather expected through Wednesday morning.

- Temperatures will be above normal through the week, with very
  warm and humid conditions arriving for the 4th of July.

- Showers and thunderstorms expected at times from Wednesday
  afternoon through much of the holiday weekend. The greatest
  rain chances occur on Saturday.

&&

.DISCUSSION...
Issued at 355 AM CDT Tue Jul 1 2025

The short-wave and associated weak surface trough that produced
scattered thunderstorms yesterday afternoon/evening have shifted
east of the region, leaving mostly clear skies across GRB CWA
early this morning. Have been watching for fog development, as
several sites in northern WI have surface RHs at or near 100
percent, but boundary layer winds of 20 to 25 knots and westerly
surface winds around 5 knots were apparently providing just enough
mixing to prevent development.

Subsidence/drying in the wake of the short-wave and the arrival
of a weak ridge of high pressure will keep the region dry today
and tonight, and likely through much of Wednesday morning.

Thunderstorm Chances Mid-Week through next Weekend: Zonal flow
will persist through Wednesday, with a weak short-wave expected to
brush through northern WI during the afternoon. A weak convergence
zone is also evident over Menominee County MI and far NE WI during
the afternoon. SBCAPE is expected to increase to 1-2K j/kg during
the afternoon, along with deep layer shear of 25-40 knots,
strongest in northern WI. SPC has outlooked much of Wisconsin
for a Marginal risk of severe, but feel that the main threat
would be across northern WI, where the better forcing and shear
are evident. Even so, think the severe threat will be isolated.
Any convection that develops should weaken as instability wanes
Wednesday evening.

A warm front is expected to lift northeast into SW WI on Thursday,
then move into the forecast area Thursday night. This front
should bring a chance of storms. A warm, muggy and unstable air
mass will reside over the forecast area by the 4th of July, but
a building upper level ridge may result in less overall coverage
of convection during the day and evening. Southwest flow, a
stronger short-wave trough and associated cold frontal passage
will likely bring a more widespread period of showers and storms
centered around the Saturday time frame. If the timing of the wave
coincides with peak heating, strong to marginally severe storms
could develop, though weaker deep layer shear of 20 to 25 kts
could be a mitigating factor. Precipitation chances should taper
off Sunday and Monday, after the front shifts east and drier air
arrives.

Temperatures: Above normal temperatures are expected through
Saturday, followed by near-normal conditions early next week.
Very warm and muggy conditions arrive for the 4th of July, with
heat indices rising into the upper 80s to middle 90s during the
afternoon.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1104 PM CDT Mon Jun 30 2025

Skies have become mostly clear in wake of the showers and storms
from earlier this evening. As temps cool overnight, some fog may
form, though it is not expected to be as dense as what occurred
last night. Only terminal that has a mention of IFR vsby is RHI.
Tuesday will feature northwest winds gusting to 15 kts and
scattered fair weather cumulus clouds with MVFR bases in the
morning, lifting to VFR in the afternoon. Skies will clear out
quickly on Tuesday evening.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......JLA