NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 221907
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
207 PM CDT Mon Jun 22 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Next chance for widespread showers and thunder Tuesday night
  through Wednesday. Small potential for isolated severe storms Wednesday
  afternoon.

- Near to below normal temperatures most of the week, then more
  summer-like conditions arrive over the weekend.

- Severe weather potential increases beginning late this weekend.

&&

.DISCUSSION...
Issued at 207 PM CDT Mon Jun 22 2026

Near term through Tuesday...Couple areas of enhanced cu noted over
northern WI and over eastern WI closer to lake breeze. Not expecting
any showers to occur as cloud depth is quite shallow. Suppose brief
sprinkles could occur. Mid and high clouds tied to 500-300 jets
stream across tonight, then skies briefly clear out Tuesday before
inreasing again late day ahead of trough and sfc low diving into
the northern Plains.

Showers and some thunderstorms Tuesday night through Wednesday
evening...Mid-level trough over the plains results in warm/moist
advection into western Great Lakes Tuesday night. Majority of
rain should not arrive over central WI until after 7 PM. MUCAPE
and shear remain on weaker side into Wednesday morning, so severe
storms appear unlikely. PWATs rise to 1.25-1.50" through the night
so moderate, perhaps locally heavy rain, could occur. Looking at
NBM, probabilities for rainfall exceeding a half inch through
Wednesday at noon is 50-70%. Probability of exceeding an inch
is up to 20-40% as some CAM guidance begins to get incorporated.
Agree with previous shift that would expect this to represent a
reasonable locally high rainfall amount, especially given meager
MUCAPE. Still looks like a break may develop later morning into
afternoon, before showers and storms redevelop during peak
heating. Shear is sufficient for severe storms, but sfc based CAPE
may be limited by earlier showers. Using blend of ensembles (LREF)
probabilities for at least 30 kts shear and 500J/kg CAPE is closing
in on 50%, but diminishes to less than 20% when using 1000J/kg CAPE.
Overall, looks like a day that could have a few strong to severe
storms in the afternoon.

Thursday continues to have some active weather in the forecast as
well, relying largely on diurnally driven instability to produce
showers. Trough is farther east, and thus stronger mid and upper
jets are displaced away from our area. MUCAPE barely reaches
500J/kg. Trends favor less shower and storm activity than it
looked like yesterday. Trend carries over into Friday which now
looks pretty dry. However, as mid-upper flow flattens, could see a
few showers work across Friday evening into Saturday morning.

After this a pattern shift is still in the works for this weekend
and beyond as upper flow becomes more amplified and a broad trough
digs into western CONUS. Warmer, moist air will surge into the
region beginning Sunday when highs reach back into the 80s and
dewpoints increase into the 60s. The warming trend will further
increase into the first part of next week as a warm front lifts
across the area with stronger LLJ. Instabiity ramps up markedly
with even mean of LREF showing sfc CAPEs over 2000J/kg by next
Monday. Given the instability and stronger 500-300mb jets in the
region, severe weather potential will be increasing. Details far
from certain as there will no doubt be convectively driven
shortwaves roaming the upper mississippi valley given the pattern.
Machine Learning continues to show increasing percentages beginning
Sunday. Certainly will be a time to watch as we get closer.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1248 PM CDT Mon Jun 22 2026

VFR conditions through the TAF period. Scattered to broken cumulus
(035-050 AGL) this afternoon with intervals of mid and high clouds
tonight into Tuesday. NE-E winds up to 10 kts this afternoon will
become light and variable tonight into Tuesday.

Looking ahead, showers and some thunderstorms will move in from
the west on Tuesday evening. Periods of moderate rain could occur
through late Tuesday night. IFR to MVFR conditions are likely by
late Tuesday night into Wednesday morning.

&&

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

&&

$$

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