NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 121840
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
140 PM CDT Tue May 12 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Scattered thunderstorms are expected to redevelop this afternoon
  and early evening. A few strong storms are possible in eastern
  Wisconsin, capable of producing small hail and wind gusts in
  excess of 40 mph.

- Windy conditions expected through Wednesday, with hazardous
  conditions for small craft on the lake and bay.

- Additional rain chances expected Late Thursday night into
  Friday, and late Saturday night through at least Monday.

- Low relative humidity (RHs 20-35%) on Wednesday and Thursday
  will result in elevated fire weather conditions.

&&

.DISCUSSION...
Issued at 140 PM CDT Tue May 12 2026

The latest RAP analysis and satellite imagery show a surface low
pressure system positioned north of Hayward, Wisconsin, early this
afternoon. An associated warm front is currently lifting across
western Wisconsin, while a trailing cold front extends into
central Minnesota. An initial round of showers and storms tied to
warm advection is currently exiting the lakeshore of northeast
Wisconsin. In its wake, clearing skies over central and western
portions of the state are allowing for significant solar
insolation. A potent shortwave is moving east across western Lake
Superior, which will serve as the primary dynamic driver for
redevelopment later today.

As the surface low and dynamic shortwave track across northern
Wisconsin this afternoon, scattered showers and thunderstorms are
forecast to redevelop after 3 pm. The highest coverage is expected
to remain north of the Highway 29 corridor where forcing is most
robust. The primary forecast uncertainty involves the degree of
destabilization; while some guidance suggests moisture pooling
could push dewpoints into the lower 50s, upstream observations in
the 40s suggest a more modest instability profile. Given the
mixing potential, storms should remain widely scattered to
scattered in nature with small hail and gusty winds as the main
threats. An isolated near- severe storm is possible over eastern Wisconsin
before activity wanes by 7 pm.

Strong cold advection will settle into the region tonight behind
the departing low. While most areas will see a decrease in
precipitation, scattered showers will likely persist across far
northern Wisconsin until late tonight. Tightening pressure
gradients will maintain breezy conditions and lead to an increase
in cloud cover overnight. These clouds will linger through
Wednesday morning before drier air and subsidence allow for
partial clearing in the afternoon. Cooler high temperatures in the
50s to middle 60s are expected for Wednesday.

The arrival of a cooler and drier airmass will lead to elevated
fire weather conditions on Wednesday and Thursday. For Wednesday,
northwest winds gusting between 30 and 35 mph will combine with
relative humidity values dropping to near 35 percent. While the
humidity is somewhat marginal, the strength of the winds will
necessitate monitoring. By Thursday, high pressure moving across
the Great Lakes will cause winds to lighten, which should
alleviate the fire weather potential despite even lower humidity
values in the 20 to 30 percent range. Patchy frost also looks
possible Wednesday night as radiational cooling allows lows to dip
into the middle to upper 30s.

Marine conditions will remain hazardous for small craft through
Wednesday evening. South winds gusting to 30 knots this afternoon
will veer northwest tonight and remain gusty through much of
Wednesday. This will maintain wave heights of 3 to 5 feet on Green
Bay and 6 to 10 feet on the Lake Michigan nearshore waters into
the evening before waves settle into the 2 to 4 ft range.
Conditions should improve by Wednesday night as high pressure
builds in.

Looking further ahead, a pattern change is expected late this week
as a ridge builds over the eastern United States. This will
transition the region into a warmer and more unstable airmass
within southwest flow. Light rain is possible late Thursday night
into Friday morning within a warm advection pattern, though
capping aloft may limit thunderstorm potential. A more significant
system is projected for the late Sunday through Monday timeframe.
As deep moisture surges into the region, with precipitable water
values potentially exceeding the 90th percentile, there will be an
increased risk for heavy rainfall and organized thunderstorms.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1206 PM CDT Tue May 12 2026

Low pressure north of Hayward will track east across northern
Wisconsin this afternoon. South winds gusting 25 to 30 kts will
veer SW-W as a cold front moves through, eventually becoming NW by
early evening. Low-level wind shear will abate early this
afternoon, though marginal LLWS returns to KRHI tonight.

Scattered showers and thunderstorms are expected to redevelop
between 20z and 01z, primarily north of Hwy 29. Small hail and
gusty winds are the main threats. While a brief severe storm is
possible, confidence in severe storm occurrence is low.

Ceilings will deteriorate to MVFR from northwest to southeast
this evening behind the front. These MVFR decks (015-030 AGL) will
persist through Wednesday morning. Scattered light showers may
linger over far northern WI through the evening. Some improvement
toward VFR is expected after 15z Wednesday, though NW winds will
remain breezy with gusts to 25 kts.

&&

.FIRE WEATHER...
Issued at 140 PM CDT Tue May 12 2026

Pine fuels have reached their peak volatility and fine fuels have
still not greened up over northern WI, so upcoming dry and windy
weather on Wednesday and low relative humidity (RHs 20-30%) on
Thursday will result in elevated fire weather conditions. Will
also need to monitor the fire weather potential on Saturday.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC
FIRE WEATHER...MPC