843
FXUS63 KGRB 051739
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1239 PM CDT Wed Aug 5 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Scattered showers (20-30%) over east-central WI this afternoon
  as slow-moving cold front sinks south.

- Fog late tonight could be locally dense, especially across
  eastern WI.

- Rounds of showers and storms possible Friday through Monday,
  though confidence in storm timing and severity remains low.

- After today, near normal high temperatures in the low to mid 80s
  through most of next week.

&&

.DISCUSSION...
Issued at 1239 PM CDT Wed Aug 5 2026

Near term through Thursday...Main concern are chances for
scattered showers this afternoon. Already added 20-30% chances
for scattered showers this afternoon especially over east-
central WI. Peak timing will be from 2p-5p. Forcing will be
provided by shortwave over northern Iowa and weak 850-600mb
frontogenesis enhanced by right entrance of upper jet. Thunder
potential low even as shower coverage will be maximized during
peak heating as MUCAPE will be well under 500 J/kg being held in
check by current cloud cover. Limited sunshine will lead to highs
this afternoon staying in the 70s for most areas.

Risk for scattered showers ends early this evening. Once clouds
clear out, temps cooling into the upper 50s and light winds could
lead to areas of fog especially northeast and east-central WI. MOS
guidance suggests that the fog could become locally dense. After
the fog diminishes early Thursday morning, expect skies to be mostly
sunny as high pressure will be overhead. Will see scattered fair wx
cu through the afternoon. Highs will be warmer than today, with
many locations reaching the lower 80s.

Shower and thunderstorm chances beginning Friday...Weak front
drops across WI Friday afternoon through late Friday night,
interacting with ribbon of higher instability (MLCAPEs 1000+
J/kg) will allow showers and scattered storms to blossom over
northern WI. Strongest shortwave and large scale lift stays north
of Lake Superior late Friday, so expect greatest coverage of
showers to stay over northern WI into Upper Michigan through
Friday evening. This is also where smaller chances of any severe
storms will be near shear over 30 kts. Smaller chances of showers
and storms will spread over the rest of the area Friday evening as
the front shifts east/southeast.

For the weekend and into early next week, western Great Lakes
region remains on edge of western ridge/heat dome. Thus we will
stay on the gradient of steeper mid-level lapse rates over the
central Plains. Better chances of more organized convection will
remain south and west, but seasonably stronger northwest flow and
any shortwaves within the flow could kick off at least a couple
rounds of showers and storms this weekend through Monday. Overall
though given lack of stronger shortwaves and/or abundant instability
pops remain pretty low throughout. Based on LREF which is blend of
ensembles, best signal for rain (probabilities of 0.05 inch or
more) would be late Saturday night, then again Sunday night
through Monday.

In terms of severe and heavy rain potential, machine learning
guidance has increased signal for possible severe nearby both
Saturday and Sunday. Greater risks are still southwest of Wisconsin
though. ECMWF EFI points to Sunday as the greater risk day, but
even then the stronger signal remains over northern IL and southern
WI. Will continue to monitor for any severe weather potential.
Similar pattern to the risk for heavy rain, with parts of central
WI placed in a marginal risk (1 of 5) for Saturday/Saturday night
and Sunday/Sunday night. Frontal boundary over the area early next
week gradually will sag south leading to lower chances for rain
by Tuesday/Wednesday.

Temperatures/smoke...Temperatures will be near normal into next
week with highs in the lower to middle 80s. Humidity levels will
be comfortable, with dewpoints reading mainly in the upper 50s to
low 60s. Elevated smoke layer departs by this evening. Another
push of elevated smoke returns on Friday ahead of the approaching
front. No significant impacts to visibility or air quality are
expected.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1239 PM CDT Wed Aug 5 2026

A few showers may impact eastern WI TAF sites through 22z. Even
with the showers, conditions should remain VFR. Very small potential
of thunder with the showers given minimal instability and weak
forcing.

Late tonight, good signal for fog developing over eastern WI.
Visibility less than 1SM in play at GRB/ATW/MTW, with 1-3SM vsby
possible at AUW/CWA. Low-levels drying out enough at RHI today to
prohibit a repeat of the fog seen there this morning. Fog will
dissipate by 14z-15z on Thursday. Rest of day will feature FEW-SCT
VFR cu, especially over eastern WI.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion