450
FXUS63 KGRB 131709
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1209 PM CDT Tue Oct 13 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A 20% chance of light rain showers exists this evening.

- Widespread rain will develop Thursday afternoon and continue
  through Friday. NBM probabilistic guidance shows a 40 to 60%
  probability of 24-hour rainfall accumulations exceeding 0.50
  inches.

- Strong northwest wind gusts of 35 to 45 mph and marine gales are
  expected Friday alongside light rain showers.

- A widespread freeze and frost are expected Friday night into
  early Saturday morning.

&&

.DISCUSSION...
Issued at 1208 PM CDT Tue Oct 13 2026

The current surface analysis shows an area of low pressure moving
east over northern Lower Michigan with a cold front extending
southwest into the central Plains. Surface high pressure centered
over the Dakotas is building eastward, driving a cold advection
regime with brisk northwest winds and widespread cloud cover
across northern Wisconsin. Upstream, a deep upper-level low is
positioned over Nevada while shortwave energy ejects across the
Central Rockies toward the Upper Midwest. Cold advection behind
the front will keep conditions mostly cloudy and seasonably cool
through Wednesday.

Light Rain And Lingering Stratus Through Wednesday: As weak
shortwave energy ejects from the western CONUS trough this
evening, a 20 percent chance of light rain showers will traverse
central and northeast Wisconsin. A pronounced mid- level dry wedge
between 5,000 and 8,000 feet will rainfall intensity, keeping NBM
90th percentile QPF under 0.05 inches area- wide. Low stratus
will surge southward overnight into Wednesday morning, getting
trapped beneath a persistent subsidence inversion. High pressure
building into the region Wednesday will maintain mostly cloudy
skies with daytime high temperatures ranging from the middle 50s
to middle 60s.

Widespread Rain Thursday Into Thursday Night: Attention then
shifts to an amplifying northern stream shortwave and associated
surface low tracking northeast across the Great Lakes Thursday
into Thursday night. Strong dynamic forcing and moisture transport
with precipitable water values reaching 180 percent of normal
will spread widespread light to moderate rain across the region
after noon Thursday. NBM probabilistic guidance reflects high
confidence in widespread measurable rain, showing a 40 to 60
percent probability of 24-hour QPF exceeding 0.50 inches. Rain
will transition to scattered showers Thursday night before the
primary low exits eastward early Friday morning.

Strong Friday Winds And Showers: Cold advection surges across the
western Great Lakes Friday morning in the wake of the departing
cyclone, dropping 850mb temperatures over western Lake Superior to
near -5 degrees C. Steep low-level lapse rates and a tight
surface pressure gradient will yield strong, gusty northwest
winds, with NBM guidance indicating a 40 to 70 percent probability
of gusts exceeding 40 mph. Over the Green Bay nearshore zones,
confidence is increasing for gale-force wind gusts. Strong thermal
instability over the lake waters will maintain scattered rain
showers through Friday afternoon before surface high pressure
builds in from the west.

Widespread Friday Night Freeze And Frost Risk: Canadian surface
high pressure settling directly over Wisconsin Friday night will
establish a very chilly airmass across the region beneath
clearing skies and decoupling winds. Overnight minimum
temperatures are forecast to plummet into the middle 20s to lower
30s across inland north- central and central Wisconsin, with
mid-30s near the Lake Michigan shore. NBM probabilistic guidance
displays high confidence in a widespread freeze, showing a 70 to
90 percent chance of minimum temperatures dropping below 32
degrees west of the Fox Valley. Rapid diurnal warming beneath
full sunshine Saturday morning will quickly burn off widespread
frost, with temperatures rebounding into the upper 50s and 60s for
the weekend.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1208 PM CDT Tue Oct 13 2026

As low pressure exits the region to the east, widespread MVFR and
IFR ceilings prevail across the region. With cold advection
occurring through the taf period, some minor improvements can be
expected through the middle of the afternoon. There may be
sufficient mixing for KGRB/KATW/KMTW to become VFR as the cloud
mass on the southern periphery breaks up somewhat. Confidence on a
return to VFR at those TAF sites is medium low.

A weak upper disturbance could bring widely scattered light
showers to the region this evening (20% chance). Impacts to the
TAF sits appear minimal.

Ceilings are expected to lower after midnight at all TAF sites.
Widespread IFR to MVFR ceilings are the expected through the end
of the TAF period.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion