NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 240612
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
112 AM CDT Wed Jun 24 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Chances for showers and storms at times through Thursday
  afternoon. A few of the storms this afternoon and evening may
  become strong or severe, producing gusty winds and hail.

- Near to below normal temperatures rest of this week, trending
  above normal and humid by early next week. Periodic chances for
  thunderstorms are also possible early next week, with the
  potential for severe weather.

&&

.DISCUSSION...
Issued at 108 AM CDT Wed Jun 24 2026

Precipitation/Thunder Chances...Radar early this morning shows
cluster of showers and thunder from southern MN into southern WI
closely tied to sfc-925mb front. Majority of lightning is downstream
of highest MUCAPE along nose of LLJ. Farther into our area, earlier
area of showers that moved into central WI faded fast, with just
some light showers and sprinkles left shifting toward the Fox
Valley and far northeast WI. Still think southern Fox Valley to
lakeshore will see expansion of showers and perhaps some thunder
late tonight through mid morning as main frontal zone is impinged
on by increasing LLJ. Beyond this, a bit murky how much additional
showers and storms form through the rest of the morning as warm
front tries to lift in from the south. Could be the wave causing
more organized area of showers and storms over central MN (well
beyond the peak of the diurnal cycle) that will serve as the
mechanism to keep a few showers and storms going for the morning
as some models show.

Better agreement that once clouds scatter out and some insolation
is realized, another batch of showers and some storms will
develop this afternoon (per HREF paintballs of 40+ dbz echoes and
higher probs of 1hr qpf >= 0.01") with the approach of main mid-
level low and sfc low. Stronger storms will be capable of hail,
gusty winds with wbzero heights 7-8kft and sufficient effective
shear. One other thing that could have to be watched is our area
being in favorable spot for non-supercell spin ups or funnel
clouds with the low overhead increasing sfc vorticity and with
steeper low-level lapse rates nearby this afternoon. Shower
chances will then slowly wane this evening as the parent trough
slides across the upper Great Lakes. Some fog could occur late
tonight, with best chances of sharply reduced visibility over
northern WI and maybe closer to Lake Michigan. Agreement on this
is not great though.

Next round of showers and some thunder will come during peak heating
on Thursday. There is a hint of a stronger wave on the west side
of the departing trough which would enhance at least the coverage
of the SHRA/TSRA. Severe weather not expected through as probabilities
of sufficient cape/shear for organized storms is pretty low (<20%).

After a quiet start to the weekend, rather abrupt switch to a much
warmer, humid and potentially stormy pattern occurs late this weekend
into early next week. After struggling to build much instability
into the region for a while, there will be no shortage of high
instability to fuel strong to severe thunderstorms by this time.
One subtle trend that shows up in ensemble data for Sunday into
Monday is far a stronger and farther west mid-level ridge over the
western Great Lakes. Result is potential to be capped at times
as strongest 500mb and 850mb jets are aimed north and west of WI,
from the northern Plains to north of Lake Superior. This type of
pattern can yield ridge rider MCSs that can at least temporarily
crash the capping as storms build into the highest instability.
Details far from certain, but modeled QPF fields are showing some
hints of this idea starting up as early as Sunday night and lasting
through early next week. Once the ridge axis shifts farther east
by mid week, could be dealing with additional convection as capping
would not be as restricting. A lot to sort out. Main takeaway at
this point is to plan on a much more active weather pattern
developing, with storm potential not tied exclusively to peak
heating of the day.

Temperatures...Below normal temperatures in the low to mid 70s
and generally comfortable humidity levels will continue through
Friday. Temperatures then warm to normal on Saturday, then surge
well above normal Sunday through early next week with the ridging
pattern change. How much the temperatures are above normal is
still a question as NBM guidance is depicting maxes that are on
the top end of all guidance for especially Monday and Tuesday.
MEX guidance (extended GFS) is aligned closer with NBM values,
but ECX (extended ECMWF) not so much. Thunderstorm coverage and
impact on effective frontal boundaries will have a big impact on
how warm we can get. Dew points will be on the rise as well by
early next week, at least into the upper 60s and perhaps into the
low to mid 70s. If the hotter and more humid idea verifies we
would be looking at a couple day stretch of heat-related impacts.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1153 PM CDT Tue Jun 23 2026

Initial batch of showers faded as it moved into central WI. A few
light showers or sprinkles could occur before daybreak, with
better chance of showers with some moderate rain from southern Fox
Valley to lakeshore toward daybreak. Based on evening trends,
have removed mention of thunder at MTW late tonight as think best
chances for thunder will remain south. Cigs will be VFR initially,
but will drop to IFR/MVFR by Wednesday morning. Visibility may
drop to MVFR where heavier showers occur late tonight.

Scattered showers may linger on Wednesday morning as a warm front
lifts through, then a brief lull occurs late morning into early
afternoon. Addditional scattered showers and some thunderstorms
then develop by late afternoon (after 20z). Greatest probabilities
(>60%) for showers will be from central to north-central WI. Not
as certain on where thunderstorms will be though, so continue to
use PROB30 groups for now (CWA/AUW) and kept with only shower
mention elsehwhere. Where storms occur, an isolated strong to severe
storm is possible with gusty winds and hail.

&&

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

&&

$$

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