NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 211728
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1228 PM CDT Sun Jun 21 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Next chance for widespread showers and thunder Tuesday night
  through Wednesday. Risk of severe weather or heavy rain is low.

- Near to below normal temperatures most of the week, then a
  warming trend next weekend.

&&

.DISCUSSION...
Issued at 1228 PM CDT Sun Jun 21 2026

Near term through Monday...High pressure will remain the main
weather feature as low pressure passes south across the Corn
Belt. North edge of shield of rain from this low will stay
south. Farther north, showers forming this afternoon across the
U.P. along the lake breeze could drift into northern WI. Only
looking at 10-20% chance of rain north of Rhinelander. Soundings
show meager CAPE and this staying below -10c isotherm, so lightning
chances appear quite low (less than 10%). Seasonably cool tonight,
especially central to north central where temps drop as low as
lower 40s. Northeast winds kick up some with gusts to 15-20 mph
behind the departing low. Strongest winds will be over eastern WI
and closer to the waters.

Showers and scattered storms Tuesday night through Wednesday...
Mid-level trough over western Canada reaches Manitoba/North Dakota
by late Tuesday. Warm/moist advection with LLJ brings showers and
some thunder into area Tuesday evening through Tuesday night.
Chance of seeing 0.25 inch of rain peaks at 30-40%, while chance
of over 0.50 inch of rain is less than 15%. Ensembles/models point
to there being a break/lull in showers sometime late Tuesday night
into Wednesday morning, with another peak in coverage of showers
during peak heating Wednesday afternoon. Forecasted instability
suggests a low chance of severe weather. Heavy rain potential is
also low. However, any increase in instability could open up
opportunity for isolated severe storms Wednesday given decent
shear present.

Additional mainly afternoon showers and storms Thursday/Friday...
Northwest flow with cooler mid-levels leads to more scattered
showers and storms Thursday through Friday, with peak of this
occurring Thursday afternoon into Thursday evening over northern
WI closer to mid-level low. MUCAPEs only reach 500J/kg, so risk
for severe storms stays low.

Warmer next weekend...
Upper heights bounce upward over the Great Lakes downstream of
stronger troughing in the west. It will become warmer overall with
highs back to or above normal. Readings may be reach the lower to
middle 80s by next Sunday. Low pressure will be over the northern
Plains and with increasing southwest LLJ downstream of building
instability aimed into the western Great Lakes, expect shower and
storm activity to increase through the weekend. Better chances
look to be on Sunday. Hints from Machine Learning that risk of
severe storms increases to our west, gradually shifting toward the
western Great Lakes. Will be something to watch. Overall, for those
looking for more summerlike weather, it will be at least trending
in that direction.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1228 PM CDT Sun Jun 21 2026

Scattered cumulus clouds this afternoon over northern WI. Isolated
showers are expected to remain north of RHI. Otherwise, broken
high clouds will stream across to the north of a low pressure
system crossing the corn belt. Rain with the low will only reach
as far north as southern WI. Skies clear out tonight, but no fog
is expected. Monday will feature mostly clear skies with just a
few fair weather cu around 5kft. NE winds will increase late
tonight through Monday, with gusts of 10-15 kts over northeast WI
terminals.

&&

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

&&

$$

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