420
FXUS63 KGRB 162340
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
640 PM CDT Sun Aug 16 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Isolated to scattered showers (10 to 30% chance) possible
  mainly along the Door peninsula this afternoon.

- Shower and storm chances (20 to 50%) return late Monday night,
  continuing through Tuesday. Potential for excessive rainfall
  and severe weather have decreased.

- Drought conditions expected to worsen due to rainfall deficit
  and little to no chances for wetting rain in the forecast.

&&

.DISCUSSION...
Issued at 1200 PM CDT Sun Aug 16 2026

This afternoon... Brief shower chances remain possible through
this afternoon mainly along the Door peninsula as weak frontal
boundary gradually shifts east. With little to no upper support
and limited instability due to cloud cover, have for the most part
kept thunder out of the forecast. Increasing gradient winds behind
the front may result in 20 mph gusts across the area through this
afternoon.

Minimal shower/storm chances... Better chances for scattered
showers and embedded thunder come Monday through Tuesday as stout
northwest flow brings another front through the upper Mississippi
Valley. Most recent suite of model runs retain the trend of
quicker and earlier FROPA late Monday night into Tuesday morning;
as such, excessive rainfall and severe potential have gone down.
Regardless, airmass behind the front doesn`t look particularly
juicy, with better moisture transport from the Gulf remaining to
our southwest anyway. WPC has thus shunted both the slight and
marginal ERO to the south, though marginal risk remains
along/south of Hwy 10. Any excessive rain potential would likely
come with training storms or repeated showers. Cannot rule out the
possibility of a diurnal storm or two, possibly on the stronger
side, as modest instability (500 to 700 J/kg) coincides with 40+
knots of bulk shear during peak heating.

Cooler and more stable air filters in behind the front on
Wednesday, with temperatures steadying out in the upper 70s to low
80s. Next period of concern would then be Friday into Saturday as
potent shortwave and attendant front traverse the Midwest. Though
storm predictability is low this far out, ML guidance paints a
broad 5 to 15% prob severe, so will continue to monitor.

Worsening drought conditions... Forecast concerns gradually shift
to worsening drought conditions due to the lack of wetting rain
we`ve received recently. Additionally, little to no relief is in
sight as better jet dynamics remain to our north with greater
moisture return/instability reserve holed up to our south. As of
August 11th, the majority of Wisconsin sits in D1 drought status
(Moderate), with pockets of D2 (Severe) drought across northwest
and north-central Wisconsin where they have received only 25 to
50% of normal precip over the past 30 days. If current dry spell
continues, fire weather concerns could come into play during late
summer/early fall due to low afternoon RHs and drying fuels.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 640 PM CDT Sun Aug 16 2026

A mix of VFR and MVFR cigs over the forecast area this evening as an
area of stratocumulus cumulus clouds continues to hang over the
region. As drier air continues to filter into the region this
evening expect these clouds to continue slowly scattering out. As
skies clear out over the Wisconsin River Valley areas of patchy
fog/low status may develop overnight. However, not confidence enough
this will impact RHI, AUW, or CWA so have left any IFR conditions
out of the TAFs for now.

Monday a few MVFR status clouds may linger into the morning, but
cigs should rise quickly through the morning leaving VFR conditions
for the afternoon.

Winds will gradually subside this evening with mostly calm
conditions overnight. Monday winds will start northwesterly and
gradually veer around to the southwest with peak gusts around 15kts
during the afternoon.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......GK

NWS GRB Office Area Forecast Discussion