188
FXUS63 KGRB 272336
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
636 PM CDT Fri Jun 27 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Periodic shower/storm chances through the weekend with the
  highest chances (50-80%) Sunday afternoon, when a few severe
  storms are possible.

- Temperatures and humidity will trend back above average
  through the weekend, with near to above average temps
  continuing into next week.

&&

.DISCUSSION...
Issued at 225 PM CDT Fri Jun 27 2025

Thunderstorm Potential this Weekend...

Transient high pressure will work across the area tonight as a short
wave trough and associated surface low trek into eastern Canada.
Light surface flow and a cool, moist boundary layer may lead to
some fog development overnight, particularly over central into
north-central Wisconsin.

Meanwhile, a few rounds of storms will impact parts of the northern
plains into the Great Lakes through the weekend. Storms forming well
west late this afternoon/tonight may spread towards Wisconsin
Saturday morning, although with instability holding mostly west of
the area into Saturday, anything that approaches likely will be
weakening, and may hold farther south and west within the unstable
air.

Additional storms should form later Saturday and Saturday night
across Minnesota into western/northern Wisconsin. The details
of this convective evolution remain unclear at this time, with
remnant outflow potentially impacting storm initiation as a
low-level jet focuses across northern Wisconsin overnight.
With the plume of instability building eastward into Wisconsin,
stronger storms could not be ruled out, especially over central
Wisconsin.

The most likely window for any severe storms comes later Sunday
as a cold front approaches. Any storms that persist from
Saturday night could impact the environment on Sunday, so there
is uncertainty how potential storm initiation may unfold. In
general, though, assuming no substantial impacts from prior
storms, expect a very warm, humid day with moderate to strong
destabilization occurring in advance of the front. Forcing does
not look overly strong and wind shear is modest. This overall
suggests scattered storms, possibly more multicell in nature.

The synoptic signal for heavy rainfall is not as pronounced as it
was in prior days with the NBM showing 24-hour probabilities for at
least an inch less than 25% across northern Wisconsin Saturday night
into Sunday. However, seasonably high atmospheric moisture (NAEFS
precipitable water exceeding the 90th percentile), rather deep
>3.5km warm cloud depths and plentiful instability suggest the
potential for localized heavier rain amounts, dependent on storm
evolution and whether particular areas are subject to repetitive
storms.

Next Week...

A mid-level trough will swing across the Great Lakes early in the
week. A few showers or storms, mainly diurnal in nature, may develop
in the vicinity of the trough with some destabilization beneath
cooler mid-level temps.

The mid-level flow transitions northwest through mid-week with
indications of some broad ridging spreading eastward towards the end
of the week. In the wake of the early week trough, there is no clear
signal for impactful precip through mid-week, however
predictability in details of the flow, including
timing/placement of any embedded shortwave troughs, decreases
through the week. In general, though, as high pressure shifts
east through the week, southerly flow/moisture is forecast to
begin to increase with some increase in shower/storm potential.
Temps generally look to be fairly seasonable heading into early
July with ensembles showing somewhat larger spread later in the
week given uncertainty in flow evolution.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 635 PM CDT Fri Jun 27 2025

MVFR CIGS will grudgingly scatter out by midnight with mostly
clear skies overnight. The clearing skies and light winds will
result in areas of fog developing after 08z-09z, especially over
central and north-central WI. IFR to LIFR conditions are expected
in the fog. Any fog will diminish after 12z with scattered mainly
VFR cu late morning into the afternoon. Scattered to broken high
clouds may move across as showers and storms diminish while moving
into western WI. There is a 20% chance that a few of the lingering
showers may reach central and north-central WI 15z-18z. Winds on
Saturday will become more southerly, but will remain less than
10-15 kts.

&&

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

&&

$$

DISCUSSION.....JM
AVIATION.......JLA