340
FXUS63 KGRB 031149
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
649 AM CDT Thu Jul 3 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Continued potential for showers and thunderstorms late tonight
  into Friday (July 4th), and Saturday through Sunday. The
  greatest chance for widespread showers and thunderstorms will
  occur Saturday and Saturday night. A low-end (Marginal) severe
  threat exists through the period, and there is potential for
  heavy rainfall Saturday into Saturday night.

- Temperatures will be above normal through the holiday weekend,
  with very warm and humid conditions expected Friday (July 4th)
  and Saturday.

&&

.DISCUSSION...
Issued at 403 AM CDT Thu Jul 3 2025

A weak boundary was sagging south across the forecast area early
this morning. Along and north of the boundary, partly to mostly
cloudy skies were observed, along with isolated showers. Wherever
clearing had occurred, patchy fog was developing.

Thunderstorm Chances through the Holiday Weekend: The weak front
is expected to shift southwest of the forecast area this morning,
stall out through the evening, then lift northeast as a warm
front late tonight into Friday. After a general lull in showers
and thunderstorms (slight chance within the area of higher
instability in C WI) through this evening, elevated storms are
expected to increase as the warm front pushes northeast. SPC HREF
shows the best concentration of 40+ dBZ paintballs occurring
across the forecast area late tonight through noon Friday.
Marginal instability and weak shear (around 20 kts) does not bode
well for organized severe weather, but a couple strong storms
with small hail cannot be ruled out. The convection should start
to wane during the afternoon as an upper level ridge builds over
the region and the warm front lifts northeast. Generally dry
conditions are expected for the Friday evening fireworks displays.

Models have trended a little slower with the weekend cold frontal
passage, with dry conditions prevailing through the overnight
Friday night, and widespread showers and thunderstorms impacting
the forecast area Saturday into Saturday night. CAPE building to
1-2K j/kg and modest deep layer shear of 20-30 kts point to a
marginal severe risk Saturday afternoon and evening. PWATs
increasing to 2-2.25 inches (200 percent of normal) supports a
threat of heavy rainfall and localized urban flooding. The slower
frontal movement leads to a continued chance of showers and storms
into Sunday, especially over the southeast CWA.

Drier conditions are expected for at least the early part of the
next work week, as high pressure and much drier air arrives in
the wake of the front.

Temperatures: Above normal temperatures are expected through
Saturday, followed by near to a little below normal conditions
through the middle of next week. Very warm and muggy conditions
arrive for Friday (July 4th) and linger over eastern WI into Saturday,
with heat indices into the lower to middle 90s. The heat and
humidity will impact outdoor activities for the 4th of July, but
heat indices fall a little short of advisory criteria at this
point.

Smoke: Smoke models show elevated smoke impacting far N/NE WI
through this afternoon, so have increased sky cover a little to
account for this. There is a very small chance of near-surface
smoke in the far north (mainly Vilas County) during the late
morning and early afternoon, but confidence is too low to add to
the forecast at this time.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 639 AM CDT Thu Jul 3 2025

Isolated showers northwest of GRB were gradually dissipating early
this morning. Otherwise SCT-BKN mid-level clouds covered much of
the forecast area. Patchy fog developed where skies were clear,
but the fog was already starting to mix out.

A mix of cumulus and altocumulus clouds will impact the region
today, with prevailing VFR conditions. A stray shower or storm
could develop in central WI this afternoon and evening, but these
should not impact the TAF sites. Later tonight, an approaching
warm front should cause showers and storms to gradually increase
across the southwest half of the forecast area. Have added Prob30
groups for thunderstorms at RHI/AUW/CWA for the last few hours of
the TAF period.

Light NE-E winds will turn SE later today into tonight.

&&

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

&&

$$

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