120
FXUS63 KGRB 021822
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
122 PM CDT Sun Aug 2 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Other than patchy ground fog early Monday morning, quiet and
  seasonable weather is expected through Monday night.

- Hazardous boating and swimming conditions south of Sturgeon Bay
  will abate this evening.

- Rain chances have diminished to 20-30% on Tuesday, but have
  increased to 60% over northeast Wisconsin on Wednesday morning.
  The severe weather risk is low on Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 122 PM CDT Sun Aug 2 2026

The latest RAP analysis and satellite/radar imagery show an
elongated area of surface low pressure stretching from Lake Erie
down into the Ohio Valley. Cyclonic flow around this system
continues to maintain low stratus along the Lake Michigan
shoreline, while fair-weather cumulus has developed inland with
afternoon heating and residual low-level moisture over northeast
Wisconsin. Meanwhile, a surface high-pressure ridge centered over
Ontario is expanding southward into the Upper Mississippi Valley
and western Great Lakes. Across the broader national picture, an
upper-level shortwave trough over the Northern High Plains will
track eastward over the next 24 to 48 hours, serving as the
catalyst for our next system mid-week.

Tonight Through Monday Night...
As high pressure continues to push into Wisconsin this afternoon
and evening, drier low-level air will advect into the state.
Heating and dry advection will lift cloud bases before skies clear
early this evening as the center of the surface high settles
directly over the area. Excellent radiational cooling conditions
under clear skies and light winds will favor ground fog
development after midnight through 8 to 9 AM Monday. While
operational model guidance continues to underplay fog potential,
upstream surface observations across northeast Minnesota and the
western Upper Peninsula showed widespread ground fog early this
morning under similar conditions. Have maintained patchy to areas
of fog in the forecast for north-central and far northeast
Wisconsin late tonight. Any fog will burn off rapidly after
sunrise Monday, giving way to abundant sunshine and comfortable
humidity. Afternoon high temperatures on Monday will reach the low
to mid 80s inland, holding in the mid to upper 70s near Lake
Michigan. Dry and quiet conditions persist Monday night under high
pressure.

Tuesday Through Wednesday Morning...
The upper-level flow pattern transitions to nearly zonal across
the northern tier of the CONUS, with flattened troughing over the
northern Plains. A cold front will approach from the west on
Tuesday, bringing the next widespread chance of showers and
thunderstorms. Frontal convergence appears to weaken as the
boundary moves into central and eastern Wisconsin late Tuesday
morning and afternoon. Forecast soundings show a stout capping
inversion in the 800 to 700 mb layer, suggesting much of the
precipitation through Tuesday evening will be post-frontal or
elevated. Modest instability with Most Unstable CAPE values of 500
to 1000 J/kg and deep-layer shear peaking around 25 to 30 knots
support only a marginal threat for an isolated severe storm.

A more impactful scenario appears to be setting up late Tuesday
night into Wednesday morning. Models show a stronger consensus on
mid-level frontogenesis strengthening on the nose of a developing
low-level jet over Iowa. This is expected to organize a mesoscale
convective complex that tracks northeastward directly across
northeast Wisconsin. While severe weather parameters remain
modest, heavy rainfall looks to be the main threat. Precipitable
water values of 140 to 150 percent of normal combined with deep-
layer flow parallel to the boundary raise the potential for
localized training and a low risk of urban or small-stream
flooding. Rain chances will diminish from west to east Wednesday
afternoon as the complex exits.

Thursday Through Sunday...
Predictability decreases significantly heading into the late week
and weekend. The slow-moving, flattened upper-level trough will
gradually slide across the Great Lakes region from Friday through
Sunday. Periodic shortwaves embedded in the flow will generate
shower and thunderstorm opportunities, though exact timing remains
uncertain this far out. Temperatures and humidity levels are
expected to hover right around normal seasonal benchmarks through
the extended period, with daily highs in the upper 70s to mid 80s
and overnight lows in the 50s to low 60s.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Sun Aug 2 2026

MVFR stratus continues along the Lake Michigan shoreline and
primarily impacting MTW late this morning. With onshore flow and
further heating, scattered to broken MVFR fair weather cumulus
has also popped over the Fox Valley that is impacting GRB and
ATW. More widely scattered and higher based cumulus has also
popped over central to north-central WI with cloud bases 4-5 kft.

As high pressure builds in from the north, advection of dry air
will gradually lift cloud bases this afternoon. MTW will be
slowest to rise to VFR, but that should occur early to mid
afternoon or by 20Z. The dry air will lead to clearing skies late
this afternoon or early this evening, which will leave mainly
clear skies for the rest of the TAF period.

The lone exception will be over north-central WI where conditions
will be favorable for ground fog development. Because fog was
noted upstream this morning, confidence is sufficiently high to
add a tempo for LIFR conditions at RHI from from 08-12Z Mon.

Breezy north winds will gust 15-20 kts over eastern WI through the
afternoon. These winds will subside this evening, resulting in
light winds through the rest of the TAF period.

&&

.MARINE...
Issued at 122 PM CDT Sun Aug 2 2026

The latest observations and forecast data continue to support
northeast winds of 15 to 20 knots and waves of 3 to 5 feet along
the Lake Michigan shoreline through early evening. Will therefore
maintain the Small Craft Advisory along the Lake Michigan
nearshore waters south of Sturgeon Bay through early this evening,
along with a high risk of rip currents on Manitowoc County
beaches. Winds and waves will gradually subside late tonight as
the pressure gradient relaxes with the incoming surface high.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 7 PM CDT this evening for WIZ050.
&&

$$

DISCUSSION.....MPC
AVIATION.......MPC
MARINE.........MPC

NWS GRB Office Area Forecast Discussion