593
FXUS63 KGRB 181155
AFDGRB

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

Updated aviation portion for 12Z TAF 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 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 12Z TAF Issuance
Issued at 640 AM CDT Mon May 18 2026

Showers and isolated storms will impact mainly the southeast half
of the forecast area this morning. This should be followed by a
lull in precipitation as capping suppresses convective
development. Showers and storms will increase again later in the
evening and overnight as a low pressure system and cold front
arrive. The greatest threat of storms and possible severe weather
is expected across central, north central and far northeast WI
between 11 pm and 4 am.

Areas of fog and very low stratus will improve as a warm front
lifts north this morning. The low clouds will be most persistent
in northern WI, where the warm front may stall out in the
afternoon. Models suggest that low clouds will return in the
evening and overnight hours.

Winds will become southerly and a bit gusty as a warm front lifts
north today. Winds will turn SW-W late tonight as the front moves
through. There may be periods of LLWS at the eastern TAF sites
after midnight tonight.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion