134
FXUS63 KGRB 120405
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1105 PM CDT Mon May 11 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Low afternoon RHs will remain a concern the rest of this 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 06Z TAF Issuance
Issued at 1102 PM CDT Mon May 11 2026

Low pressure over south central Canada sends a warm front across
WI late tonight. A band of showers will develop late tonight over
western WI, spreading across all TAF sites by 12z-13z 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. Appears
there will be enough instability ahead of the front to produce
isolated TSRA after 21z/22z over eastern WI. Have kept PROB30
groups for TSRA at GRB/ATW/MTW 21z-24z to cover this low-end
potential that is supported by some CAMS. Any stronger storm could
produce brief gusty winds and small hail. Not enough confidence to
place that in the PROB30 groups though.

E-SE winds ramp up through the overnight as the warm front and
low-level jet aloft approach from the west. 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 Tuesday
and remain gusty as the front sweeps through on into Tuesday night.
LLWS will become a concern Tuesday morning as the warm front
shifts through. The LLWS will end by afternoon, except at MTW
where it persists until around 00z.

&&

.FIRE WEATHER...
Issued at 1102 PM CDT Mon May 11 2026

Low afternoon RHs (25 to 35%) will continue to be a concern
this week, though periods of showers, light winds, and cooler
temperatures should prevent critical fire weather conditions most
times.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion