244
FXUS63 KGRB 201153
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
653 AM CDT Thu Aug 20 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Shower/storm chances (20-50%) arrive this afternoon across
  north-central WI, spreading across the entire area tonight
  (40-75%). Isolated-scattered showers/storms on Friday.

- While a few stronger storms could produce brief gusty winds,
  small hail and brief heavy downpours, widespread severe weather
  is not expected. A drought busting rain is not expected.

- Near seasonable temps expected into next week, although some
  cool nights are expected over the north.

&&

.DISCUSSION...
Issued at 138 AM CDT Thu Aug 20 2026

Today through Friday...A dry start to the day with only a few mid
and high clouds around. Clouds will increase through the day,
with a 20-50% chance of mainly light showers, with a stray storm
also possible, arriving across north-central WI this afternoon as
a shortwave and push of WAA approach. Most CAMs have this area
waning as it heads southeast, away from the better moisture and
forcing. Anticipate additional shower and isolated storm
development this evening into tonight as the shortwave and cold
front move across northern WI. Prospects for severe weather are
low this afternoon into tonight, with the better pool of instability
to our west and the better dynamics not arriving until tonight.
MUCAPE does climb up to 1000 J/kg, so a strong storm is possible
with some gusty winds and small hail, especially if activity can
get organized to our west and make it in central or north-central
WI.

On Friday, the area of showers and isolated storms will exit
to our east early in the day, with only some isolated activity
behind it through the morning hours. Then, as the cold front
arrives in the late morning and afternoon, another round of
isolated to scattered showers and storms is expected, especially
across eastern WI. South/southwest winds will usher in better
moisture, with dewpoints climbing into the mid-upper 60s over the
east. If we are able to get some sunshine, SBCAPEs would climb up
to 1500-2000 J/kg. Bulk shear does seem to be lacking though,
with 0-6km shear only around 15-20 kts, along with a weak capping
inversion in place, which would limit organization/strength of any
storm. So a pulsy type stronger storm will be possible, mainly
over eastern WI in the afternoon. While brief heavy downpours are
possible in any storm (PWATs up to 1.5"), widespread heavy
rainfall is not expected. High temps in the 70s are expected over
northern WI, with some low 80s expected further south. Temps
tonight will not be as cold with lows mainly in the mid 50s to mid
60s.

This Weekend...northwest flow will prevail across the Great Lakes.
A weak trough and area of increased moisture will move across the
area on Saturday, bringing the chance (20-45%) for some showers,
especially across eastern WI. Dry conditions are expected on
Sunday as high pressure spreads across the western Great Lakes.
High temps are forecast be near or slightly below seasonal norms,
with a couple chilly nights over the north with lows in the 40s.

Next Week...dry conditions continue into Monday with the next
chance of showers and storms arriving Tuesday or Wednesday with
another shortwave and frontal boundary. Unfortunately, rainfall
totals over the next week are not expected to help the drought
conditions across the area, and most likely make them worse in
spots. Temps will remain pretty steady next week, with highs in
the mid 70s to low 80s most days and lows in the mid 40s to low 60s.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 653 AM CDT Thu Aug 20 2026

VFR conditions will continue into this evening with mid and high
clouds spreading across the region. Flying conditions will
deteriorate overnight into Friday morning as clouds lower and
thicken, and showers and a few storms move across the area. As the
activity moves east, chances for thunder will decrease due to
waning instability, so will not include thunder at GRB/ATW/MTW.
Will use PROB30s for the thunder chances at RHI/AUW/CWA (though
these will likely need to be made TEMPO groups if the latest CAMs
continue to agree on the timing/extent of thunder) and then use
some TEMPO groups late tonight as some lingering showers along
with lower ceilings will be possible.

Light and variable winds this morning will become south/southwest
5-15 kts later this morning and afternoon and remaining mainly
under 10 kts tonight. Winds at MTW will turn to the S/SE later
this morning and afternoon.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......Bersch

NWS GRB Office Area Forecast Discussion