444
FXUS63 KGRB 180742
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
242 AM CDT Mon May 18 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Strong to severe storms and locally heavy rainfall possible at
  times through tonight. The greatest coverage of storms will
  occur across the northwest half of the forecast area early this
  morning, and again in the late evening and overnight hours
  tonight.

- Drier and cooler weather returns mid to late week. Frost or
  freeze headlines may be needed over mainly northern WI Tuesday
  night and Wednesday night.

&&

.DISCUSSION...
Issued at 239 AM CDT Mon May 18 2026

A cluster of strong thunderstorms was ongoing over north central
WI early this morning, in advance of a short-wave trough. This
activity had marginal instability (MUCAPE 1000-1500) and strong
deep layer shear (45-50 kts) to work with, and a few storms were
pulsing to near-severe levels and exhibiting mid-level rotation at
times. A marginal severe threat will continue over north central
and perhaps far northeast WI through about 5 am. Otherwise, low
clouds and areas of fog (locally dense) covered much of the
region, and temperatures were stuck in the upper 40s to middle
50s. A warm front was situated across southern WI, where
temperatures were in the lower to middle 70s.

The warm front will lift north today, but there is some question
if it will reach northern WI this afternoon. As the front lifts
north and daytime heating commences, the foggy conditions should
improve this morning. Have lowered max temperatures several
degrees, especially over northern WI. Still expecting decreased
coverage of storms today due to cloud cover, capping, a weakening
low-level jet and weak mid to upper level ridging. Decreasing deep
layer shear should also result in a lesser threat of severe storms
during the day. Will keep slight chance to chance pops through
the day and into the early evening hours.

A surface wave will lift into north central WI later this evening,
followed by a cold frontal passage during the overnight hours.
CAMs show an uptick in thunderstorms over central and north
central WI later in the evening, with a linear MCS moving through
mainly north central and far northeast WI during the overnight
hours. The late night timing of this is not especially favorable
for severe storms, though MUCAPE of 1000-1500 j/kg and deep layer
shear increasing to 35-50 kts supports severe potential.

The cold front sweeps through eastern WI Tuesday morning with
lingering showers and a few storms, but dry weather returns by
afternoon. Tuesday will be a windy day with west to northwest
winds gusting to 25 to 35 mph. Temps over eastern WI will remain
above normal with highs in the low to mid 70s, but cooler readings
in the 50s and 60s are expected farther west.

High pressure will bring dry and cooler conditions for the middle
of the week, with potential for frost or freeze headlines Tuesday
night and Wednesday night. Warmer temperatures and small
precipitation chances return for the weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1238 AM CDT Mon May 18 2026

Scattered to widespread rain and thunderstorms are expected
overnight as a line of convection moves in from the west. Isolated
severe storms are possible in central and north-central WI within
this line through ~09Z, with hail and wind gusts of 40 to 60 mph.
However, the threat for severe storms at any one location is low.
The more likely hazard is brief, heavy rain. Timed out best
window for TSRA at each TAF site and included PROB30 groups.
Meanwhile, mainly LIFR conditions are expected through the night
due to low clouds and fog. Some improvement from south to north
late tonight as a warm front lifts north.

Thunderstorm potential should diminish by ~12Z Monday morning,
with some lingering showers through mid-morning. Uncertainties
arise after this, but the general consensus shows a cap in place
for Monday which would limit any thunderstorm develop during the
afternoon and evening, along with MVFR and VFR flying conditions.
There is a greater threat for storms after 03Z/Tue as another
line develops to the west and moves into the area.

LLWS develops continues overnight and diminishes around 12-13Z.
Easterly surface winds will veer to the south overnight, becoming
southwest on Monday. Gusts up to 25 kts are possible at times.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......KLJ

NWS GRB Office Area Forecast Discussion