NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 181811
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
111 PM CDT Thu Jun 18 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Scattered showers and isolated thunderstorms this afternoon
  and evening may produce small hail and gusty winds, primarily
  north of Highway 29.

- Scattered rain showers and thunderstorms will bring a 50-70%
  chance of rain Friday night, with a few storms also developing
  on Saturday afternoon.

- Near to below normal temperatures and comfortable humidity will
  prevail through next week.

&&

.DISCUSSION...
Issued at 110 PM CDT Thu Jun 18 2026

The latest RAP analysis and satellite/radar imagery show
flattened troughing in the upper levels across the northern Plains
and Great Lakes. Northwest winds have been breezy so far today
with gusts to 25 mph. Lingering strato-cu from the overnight
period in cyclonic flow has evolved into a widespread fair weather
cumulus field across northeast Wisconsin. The first showers may
be developing over north-central WI at 1 PM. With further warming
this afternoon and help from a weak shortwave impulse over
northern Minnesota, widely scattered showers and a few storms are
expected to develop from 1-3 pm over north-central WI before
moving southeast through about mid-evening. Showers will be most
concentrated north of Highway 29. With surface based instability
up to 800 J/kg, there is a 10% chance that a storm could produce
brief gusty winds to 30 or 35 mph and small hail, but organized
severe weather is not expected. The shower activity should exit or
diminish by late evening, which should set up a mostly clear and
cool overnight period with low temperatures falling into the mid
40s to lower 50s.

On Friday, a mostly sunny start to the day will give way to
increasing clouds as a strong shortwave currently over Alberta
tracks towards the northern Mississippi Valley in the afternoon.
Showers and thunderstorms will likely be impacting Minnesota
during the afternoon before approaching north-central WI by late
afternoon into the evening. The combination of instability,
position of the low level jet, and HREF updraft helicity tracks
indicate that the primary severe risk will likely remain west to
southwest of the region. However, a few clusters of storms could
move into central and north-central WI after 5 pm. There are some
indications that these storms could contain gusty winds and small
hail with surface based CAPE of 500-800 J/kg and deep layer shear
up to 30 kts. More favorable parameters for severe weather will
likely set up over southwest WI. Highs on Friday will recover into
the low to mid 70s.

Long Term...Friday Night through Wednesday

Persistent upper troughing will encompass the Great Lakes to New
England region over the next week. With northwest flow aloft, this
weather pattern will favor near to below normal temperatures and
comfortable humidity levels. Daily maximum temperatures through
the weekend and into early next week will generally range from the
upper 60s to upper 70s, with overnight minimums consistently
dipping into the mid 40s to mid 50s.

The northwest flow will remain energetic, however, as several low
amplitude shortwaves will provide periodic rain chances from this
weekend into the middle of next week. Rain chances have increased
to 50-70% across the entire area on Friday night as the primary
shortwave tracks through, bringing a good chance of thunderstorms,
particularly over north-central WI. Other pop up storms are
possible over far northeast WI on Saturday afternoon primarily
driven by diurnal instability. Another broad upper level trough
will settle over the area from Tuesday through Thursday, bringing
more periodic shower and storm chances. Severe thunderstorm
chances will remain low throughout the extended period, however,
as the reservoir of significant instability will be suppressed
well south of the region. Overall precipitation amounts look to be
below normal despite the multiple distinct chances for rain.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1226 PM CDT Thu Jun 18 2026

An unsettled weather pattern will continue for the rest of the
day, with cumulus clouds building through the afternoon. A weak
upper disturbance could generate a widely scattered showers and a
few storms between 3 and 8 PM roughly. Maintained the prob30 group
for showers at RHI and added a prob30 to GRB and ATW. Otherwise,
high end MVFR to low end VFR ceilings early this afternoon will
rise to 4-5 kft.

Clearing skies late this evening before clouds (VFR) build with
daytime heating late Friday morning.

Gusty northwest winds to 20 kts at midday will continue through
the afternoon before subsiding. Gusts to 15 kts are likely on
Friday.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC