415
FXUS63 KGRB 111923
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
223 PM CDT Mon Aug 11 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Good chance of thunderstorms Tuesday afternoon over northeast
  and east-central Wisconsin, with a Marginal Risk (level 1 of 5)
  of severe storms. Primary hazards will be damaging winds and
  hail.

- Dry weather and more comfortable humidity arrive mid-week. Hot
  and humid conditions then return toward the end of the week,
  accompanying additional rain/storm chances over the weekend.

- Wildfire smoke from Canada may impact air quality mainly over
  central and northern Wisconsin. An Air Quality Advisory is
  currently in effect through 3 PM Tuesday.

&&

.DISCUSSION...
Issued at 221 PM CDT Mon Aug 11 2025

Short Term...Tonight and Tuesday

Weak cold front, generally lowering the humidity levels (as seen
by the upper 50s dewpoints now over northern WI), moves through
this afternoon, only to be followed by another cold front that
could generate some storms on Tuesday. A few of the storms could
be strong to severe. Other issue is wildfire smoke that may impact
air quality through Tuesday afternoon.

Precipitation and Thunderstorms: Two main chances of showers and
storms through Tuesday night. First arrives late tonight as
shortwave causing some showers and storms over the central Plains
this afternoon lifts east-northeast into the western Great Lakes.
Southeast forecast area will be along and north of the wave so at
least a few showers will result very late tonight through Tuesday
morning. Elevated instability of at least 500j/kg will support the
mention of non-severe storms. HREF 1hr QPF indicates greatest
coverage will stay south and southeast. Almost appears the bigger
impact from this morning convection may be to leave decent amount
of mid clouds across the area into Tuesday afternoon, which could
hold down instability compared to if we had full insolation to begin
the day.

MLCAPEs by early afternoon were forecast recently to increase to
over 1000 j/kg if not 1500 j/kg, but given the morning convection
from the plains wave, think that may end up being on the higher
side. Dynamics remain decent though with stronger cold front
approaching, shortwave trough, and right entrance region of upper
jet which all combine to boost shear to at least 35 kts. SPC has
retained Marginal Risk, but extent of instability will likely hold
key for how many strong to severe storms occur. Machine learning
progs and HREF paintballs for 40+ dbz point to 1-7 PM remaining
most likely window for severe weather if it were to occur. Area
most favored is northeast WI across Door County into east-central
WI. Damaging wind gusts and hail are the primary hazards. Mean
storm motion will be from west to east. Showers and storms exit
quickly Tuesday evening as drier air arrives behind the cold front.

Smoke/Air Quality: Smoke is evident over MN this afternoon per
GeoColor satellite with sfc obs showing many sites with vsby less
than 5 miles and haze. RAP and HRRR are underdoing extent of sfc
based smoke over MN, but extrapolating those forecasts some of the
sfc smoke will graze, especially across northern WI later tonight
into Tuesday morning. Farther south and east, only patchy smoke
will occur. An Air Quality Advisory is in effect until 3 PM on
Tuesday for all but Manitowoc, Calumet and Winnebago counties.

Long Term...Tuesday Night Through Monday

Long-term leg of the forecast mainly sees a continuation of the
currently active pattern. This being said, we may be afforded a
brief reprieve from rain/storm chances Wednesday and Thursday as
Canadian high pressure encroaches on the Great Lakes from the
north. Isolated to scattered showers associated with a mid-level
shortwave will then be possible over northern Wisconsin Thursday
afternoon, though any instability will be holed up along a cold
front to the west.

Noteworthy of mentioning is the potential for more robust rain/storm
chances that arrive over the weekend. Yet another slow-moving
cold front is progged to drop south across Wisconsin on Saturday,
possibly becoming pseudo-stationary into next week. Though much
too soon to discern any finer details, initial impression from
long-range guidance paints a picture for at least another heavy
rain threat as PWATs reach the 90th+ percentile relative to climo.
Instability likewise builds within moisture reserve along of and
ahead of the cold front during peak heating. As it stands now,
CSU machine learning algorithm highlights 15 to 30% severe probs
over central and east-central Wisconsin Saturday afternoon.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1251 PM CDT Mon Aug 11 2025

Scattered to broken MVFR-VFR cu this afternoon. VFR conditions
through the night, though some broken MVFR stratus may try to
form late at RHI. At this point, not as much as chance of low
stratus and/or fog as we have seen the last two nights.

A weak upper disturbance will bring the chance of showers and
possibly an isolated storm to east central WI toward sunrise and
on through Tuesday morning. Mix of MVFR and VFR CIGS with this
activity. Additional storms may occur on Tuesday afternoon over
northeast and east-central Wisconsin. Potential these could
impact GRB/ATW/MTW.

&&

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

&&

$$

DISCUSSION.....JLA/Goodin
AVIATION.......JLA