NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 120004
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
704 PM CDT Mon May 11 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Elevated fire weather conditions continue for the remainder of
  the afternoon due to low relative humidity. Low afternoon RHs
  will continue to be a concern throughout the week, though
  periods of rain and light winds will limit critical fire weather
  potential.

- Scattered showers (70 to 90% chance) arrive Tuesday morning. A
  few storms possible over east-central and far northeast
  Wisconsin Tuesday afternoon.

- Temperatures gradually warm during the middle to end of the
  week, reaching into the low 80s by the weekend. Better storm
  chances may accompany the warmer temperatures and better
  instability.

&&

.DISCUSSION...
Issued at 1232 PM CDT Mon May 11 2026

Surface high pressure continues to sit and spin over Lake Superior
this afternoon, shifting winds to the south as we get caught
under return flow. Stratus deck has been slow to erode over
northeast Wisconsin, though fair weather cu field has developed
over the past couple of hours. Lake breeze gradually began to
kick in, resulting in afternoon temperatures along the lakeshore
reading a solid ten degrees cooler than inland areas.

Rain/storm chances... Synoptic flow amplifies this week, bringing
several chances for showers/storms through the weekend. The first
of these chances arrives late tonight into early Tuesday morning
as a clipper low skirts the US/Canada border, bringing a round of
scattered showers to most of northeast Wisconsin. The brunt of the
rain should fall early Tuesday morning in conjunction with a push
of WAA and PWATs nearing one inch, coming to an end by around
18Z. However, QPF should remain on the lighter end, with HREF
probabilistic guidance showing a 40 to 70% chance for receiving
0.25" of rain, dropping off steeply to only 10 to 20% for
receiving 0.5". Best thunder chances will be associated with re-
development Tuesday afternoon as more potent shortwave energy
accompanies cold FROPA. Brief window with modest instability (~800
to 1,000 J/kg MUCAPE) and decent lapse rates (6 to 7C/km) arises
during this time, which would support at least some rumbles of thunder
mainly over portions of east-central and far northeast Wisconsin.
However, severe weather is not expected.

Southerly flow regime takes over mid-week as a warming ridge
builds over the central CONUS. As such, above normal temperatures
and instability begin to develop under the ridge through the end
of the week. Highs gradually increase into the upper 70s and even
into the low 80s by this weekend, holding steady in this range
into the beginning of next week. More robust storm chances will
accompany the warmer temperatures at the end of the week, though
it is still too early to pin down exact timing and severe threat
this far out.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 703 PM CDT Mon May 11 2026

Low pressure over southern Canada sends a warm front across WI
late tonight. A band of showers will develop after midnight over
western WI, spreading across all TAF sites by 12z on Tuesday.
Showers will shift east through the morning ending by early
afternoon (accompanied by MFVR to lower VFR cigs). Some showers
with MVFR cigs will continue at RHI in the afternoon closer to
the parent sfc low pressure tracking over Upper Michigan. VFR
cigs elsewhere and there could even be brief partial clearing.

Eventually the cold front tied to the low moves into central WI
late in the afternoon. In response, expect another round of
showers (more scattered in coverage compared to the morning) to
develop at the rest of the TAF sites. Cigs will be VFR. It appears
there will be enough instability forming ahead of the front to
produce isolated TSRA after 21z/22z over eastern WI. Have placed
a brief PROB30 group in for TSRA at GRB/ATW/MTW 22z-24z to cover
the low-end potential. If any stronger storms are present they
could produce brief gusty winds and small hail.

E-SE winds will ramp up this evening and through the overnight as
the warm front and low-level jet aloft approach from the west.
By late tonight, wind gusts will reach over 25 kts in central and
north-central WI. Winds shift to S/SW on Tuesday morning all areas,
with gusts of 25-30 kts possible into the afternoon. Winds shift
NW late and remain gusty as the front sweeps through. LLWS will
become a concern Tuesday morning as the warm front shifts
through. The LLWS will ease in the afternoon, except at MTW.

&&

.FIRE WEATHER...
Issued at 1232 PM CDT Mon May 11 2026

Elevated fire weather conditions persist this afternoon as high
pressure sits and spins over the Great Lakes. RHs have fallen
into the upper 20s to mid 30s across the sandy soil regions,
though winds remain light. A lake breeze then kicks in later this
afternoon and evening, bringing in a modified marine airmass that
will regulate humidity. Low afternoon RHs (25 to 35%) will
continue to be a concern throughout the week, though periods of
showers, light winds, and cooler temperatures should prevent
critical fire weather conditions.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......JLA
FIRE WEATHER...Goodin