813
FXUS63 KGRB 022125
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
425 PM CDT Wed Jul 2 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Ongoing thunderstorms this afternoon with an isolated,
  marginally severe threat.

- Continued potential for rain and thunderstorms from Thursday
  through Saturday, with the greatest chance for widespread
  showers and thunderstorms occurring on Saturday.

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

&&

.DISCUSSION...
Issued at 425 PM CDT Wed Jul 2 2025

Ongoing Storms...An approaching weak shortwave and daytime
heating has lead to the development of thunderstorms this
afternoon. These were originally located across northern MN this
morning, weakened, and then redeveloped across northern WI early
this afternoon. As of 2030Z/Wed this cluster of thunderstorms was
ongoing across central into east-central WI. So far, the highest
report has been for pea sized hail, with radar indications there
could be hail up to about half an inch. A gust to 43 kts (50 mph)
occurred around 3:15 PM at Mountain, but otherwise radar
indicates there could be gusts up to 40 mph within the strongest
cells. This cluster of storms will continue to track SE over the
next few hours, reaching the Green Bay area by 22Z/5PM CDT based
on the current speed. CAPE and shear are somewhat modest, with
MUCAPE up to about 1000 to 1500 J/kg across the forecast area,
with 0-6km shear around 30 kts. Large scale forcing is also weak.
This should act to mostly limit severe storm organization, however
with model soundings showing good inverted V`s with low level
lapse rates around 9-9.5 C/km, isolated severe gusts to 60 mph
remain possible within the strongest storms. Cannot rule out some
larger hail, but this is a secondary concern.

Tonight...CAMs have struggled greatly with handling today`s
precipitation, so confidence in the forecast beyond the next
couple hours is low. Most likely scenario is for this first
cluster of storms to track southeast of the area by mid-evening.
Uncertainty arises with whether another cluster of showers/storms
may develop along a weak frontal boundary moving south across WI
late tonight. Paintballs generally say yes, as do CAMs, but most
CAMs painted a dry picture this afternoon which was inaccurate.
The global models may be handling the setup better, but are split
on later development. Regardless, instability will wane by that
point, so the severe storm potential would be low. Stuck with
isolated to scattered showers and with a few thunderstorms along
the front overnight.

Rest of the Forecast...Most of Thursday is shaping up to be dry
as the overnight front moves south of WI. However, it pushes a bit
farther north during the afternoon coinciding with peak heating.
The southwest part of the forecast area, primarily central WI,
could once again see some isolated/scattered showers and storms
during the afternoon. Overall severe potential is low, but
isolated strong wind gusts and hail could occur within the
strongest cells. This front then moves farther north on Friday,
with some isolated development possible along the front again.
Similar to the previous days, localized strong gusts and hail
cannot be ruled out, but overall severe potential is low. Most
models have this moving north of the state by Friday evening,
allowing for dry weather during any evening holiday fireworks.

Forecast confidence increases on Saturday as there is higher
consensus in a shortwave and surface cold front tracking across
from NW to SE. CAPE values Saturday afternoon are around
1000-1500 J/kg, shear around 30-35kts, and pwats rising to 2.0" or
higher in spots. The main concern is the potential for heavy rain,
with perhaps another low-end severe thunderstorm threat.

Precip associated with this cold front should clear out Sunday
morning or early afternoon, followed by cooler and dryer weather
for the end of the weekend into early next week.

Temperatures...The above normal temperatures and humid conditions
will continue through Saturday, peaking Friday and Saturday with
high temperatures in the mid 80s to low 90s, and heat index values
in the upper 80s to middle 90s. While this is below the level in
which a Heat Advisory is issued, it is still recommended to
exercise heat safety by staying hydrated, wearing light clothing,
and applying sunscreen.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 107 PM CDT Wed Jul 2 2025

As of 18Z VFR conditions were noted area-wide with afternoon cu
starting to develop with bases around 4-7kft. Meanwhile, more
substantial cu and weak precip returns were noted in north-central
WI in association with a shortwave coming through. Models have
varied on the handling of afternoon precip, but given the current
development have followed the meso models which show this. A
broken line of showers and some storms will likely develop across
northern WI, and track south through the afternoon and early
evening. Included most likely timing of rain/storms in PROB30
groups, although TEMPO for KRHI where coverage will be a little
better. Dips to mainly MVFR likely within any heavier rain and
thunderstorms.

Activity clears out mid-evening, although still seeing hints at a
few widely scattered showers overnight. Likelihood too low in
include in TAFs, but a few may be around. Meanwhile, fog
development across central and north-central WI late tonight will
likely bring vsbys down to IFR levels for a couple hours.

Winds will generally be from the west around 5-10 kts through
mid- evening, and then subside to light in variable, settling to
the E/SE on Thursday. Gusts of 30-40+ knots could occur within any
thunderstorms.

&&

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

&&

$$

DISCUSSION.....KLJ
AVIATION.......KLJ