NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 120827
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
327 AM CDT Tue May 12 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Showers (50-80% chance) and isolated thunderstorms overspread
  the region this morning, then exit mid-day. Scattered showers
  and storms redevelop later this afternoon. A few strong to
  marginally severe storms possible over mainly east central WI
  from 3-7 pm.

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

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

- Above normal temperatures expected later this week into early
  next week.

&&

.DISCUSSION...
Issued at 326 AM CDT Tue May 12 2026

High pressure and temperatures in the 30s lingered over far
eastern WI early this morning, but developing south winds and
increasing WAA combined to boost temperatures into the lower to
middle 40s farther west. Despite abundant dry below 500 mb (seen
on the 06z/Tue GRB sounding), strong WAA on the nose of a 40-50
kt LLJ and mid-level frontogenetic forcing was generating showers
and isolated thunderstorms in central and north central WI. WV
imagery showed a potent short-wave trough moving into NW MN. A
more concentrated area of storms was developing ahead of this
feature.

WAA showers and embedded elevated thunderstorms will overspread
the forecast area this morning. These showers should exit eastern
WI by around noon, followed by partial clearing, with subsequent
heating leading to modest SBCAPE of 400-800 j/kg over mainly
central and east central WI. As a cold front and the previously
mentioned short-wave move through in the mid to late afternoon,
scattered showers and storms should redevelop. Despite the
marginal instability, moderate to strong deep layer shear and
synoptic forcing should be sufficient to generate a few strong
storms capable of producing hail and gusty winds. SPC has
pushed the Marginal risk of severe storms farther north, covering
roughly the eastern two-thirds of the forecast area. This may be
a bit too far north, as temperatures over the Northwoods will
likely remain in the 50s and lower 60s, in sharp contrast to the
upper 60s and lower 70s anticipated over central and east central
WI. Winds will gust to 25 to 35 mph from the south ahead of the
cold front today, then from the northwest tonight into Wednesday.
Scattered showers linger over mainly northern WI this evening.

High pressure arrives later Wednesday into Thursday, with
associated dry conditions lngering into Thursday evening.

Another frontal system arrives Thursday night into Friday, with
showers and embedded storms expected.  After a brief dry period
Friday night into Saturday evening, a pattern change to southwest
flow aloft will commence. As this occurs, a cold front will
move slowly through the region, interacting with a surge of Gulf
moisture (PWATs of 1.25 to 1.75 inches) and instability, and
producing periods of showers and storms from late Saturday night
through Monday or Monday night. The pattern supports potential
for heavy rainfall, but models area all over the place regarding
timing and placement.

Temperatures will remain below normal over northern WI today
and across the entire forecast area on Wednesday, but are
expected to climb above normal late this week into early next
week.

&&

.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 326 AM 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.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......JLA
FIRE WEATHER...Kieckbusch