644
FXUS63 KGRB 190004
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
704 PM CDT Mon May 18 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Isolated severe storms possible through tonight. Greatest
  coverage of storms northwest part of the area late this evening
  and overnight.

- Drier and cooler mid to late week. Frost or freeze headlines may
  be needed Tuesday night and Wednesday night.

- Warmer by next weekend with return of rain chances.

&&

.DISCUSSION...
Issued at 142 PM CDT Mon May 18 2026

Main concern is chance of severe storms through tonight ahead of
an approaching cold front. Modified warm front is working through
the area from the south. It is running into affects from earlier
storms to south and southeast. Subsidence to west of storms over
Michigan is resulting in minimal re-development of showers and
storms thus far. Decent cu field is blossoming over western WI
into central WI, but capping is noted on forecast soundings in
these areas rest of the day. Lowered pops to slight chance all
areas through 5p. An warm and certainly more humid day by recent
standards.

Primary convective development this afternoon into early evening
will be well to the south over the central Plains. As the warm
front lifts north, it could be enough to overcome the capping for
a few storms to develop, especially northern WI. Isolated strong
storm is possible with MUCAPE up to 1000J/kg and effective shear
of 30-40 kts. Severe threat will be higher if a storm could
become truly surfaced based and occur near the front. Wave to
north of this convection over the plains along with approaching
sfc low looks to bring best chance of a line of storms late this
evening into the overnight hours for central and north-central WI.
Main hazard with these storms will be gusty winds and heavy rain.
Isolated damaging wind gust could occur if line remains more
organized as it moves into the area. Overall the chance for severe
weather this afternoon through tonight has trended downward as SPC
has trimmed the Slight Risk out of all our forecast area.

Leftovers of this overnight line of storms shift by late tonight.
A few showers or storms may linger through the morning over eastern
WI, just ahead of cold front. The front sweeps through by early
afternoon, shifting southwest winds to northwest. Winds will be
gusty up to 30 mph. Highs could touch 70 over eastern WI, but will
be in the 60s for most, with even some 50s over north-central WI.

Beyond Tuesday, rest of the week looks generally dry. Canadian
high shifts across late Tuesday through Wednesday night. Frost or
freeze headlines may be needed Tuesday night and Wednesday night,
especially northern WI. Greatest risk is Wednesday night with
high overhead and PWATs less than 0.5 inch. Min RH will be low Wed
through Fri afternoon`s. Return flow kicks in late this week into
next weekend with highs steadily returning to at or above normal.
Chances for rain and perhaps some thunder increase by next weekend.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 704 PM CDT Mon May 18 2026

Continued dry weather and VFR flying conditions are expected
through most of the evening (through ~05Z). A few showers could
pop up earlier at KRHI, and fog off Lake Michigan will impact vsby
at KMTW.

A line of rain and thunderstorms is expected to move into central
and north-central WI around 04-05Z. This will be accompanied by
lowering cigs to MVFR/IFR along with lower vsbys during periods of
heavy rain. A brief window of strong to severe storms exists from
~05-09Z in central and north-central WI (including KAUW, KCWA,
and KRHI) with wind gusts to 60 mph and small hail possible.
Otherwise, main impacts will be lightning, brief heavy rain, and
stronger wind gusts. By the time this line gets to eastern WI it
will likely weaken significantly. Included PROB30 groups for east-
central WI TAF sites as confidence in any thunderstorms reaching
these locations is low. Showers linger through ~13-14Z Tuesday
morning, then dry weather is expected for the rest of the day.
IFR/MVFR cigs are forecast through Tuesday morning in the wake of
the precipitation, with improvements to MVFR/VFR in the afternoon.

South winds veer southwest overnight, and then veer to the west-
northwest Tuesday behind the cold front, along with wind gusts to
25 kts.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......KLJ

NWS GRB Office Area Forecast Discussion