221
FXUS63 KGRB 180326
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1026 PM CDT Mon Aug 17 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Scattered showers (30 to 50% chance) and an isolated storm
  possible late tonight.

- Scattered showers and storms (30 to 60% chance) back on for
  Tuesday. Marginal risk (level 1 of 5) for severe storms over
  part of central Wisconsin, though greatest severe risk is still
  to the south.

- Rain chances return on Friday, though are not expected to be
  drought busting.

&&

.DISCUSSION...
Issued at 1200 PM CDT Mon Aug 17 2026

Tonight/Tuesday... Broken line of showers/storms on the nose of
LLJ should become scattered upon entering north-central Wisconsin
late this evening into tonight. Any remnants should diminish by
the time they reach east-central Wisconsin as they outrun axis of
better instability and LLJ shifts north.

Forecast looks back on track for conditional severe weather
threat Tuesday afternoon and evening as CAMs show a slower
progression of the front. Not quite sold on this as of yet given
the volatility of front timing over the past several days, though
as of right now, it looks like FROPA interacts with corridor of
decent instability (1,000+ J/kg) during peak heating Tuesday
afternoon. Bulk shear exceeds 40 knots during this time as well,
which warrants the slight northerly nudge of the marginal risk
into portions of central Wisconsin in SPC`s Day 2 Convective
Outlook. However, worth noting is that ML CAM viewer still doesn`t
seem that impressed with severe probs over northeast Wisconsin.
Nevertheless, main threat with any stronger storms would be gusty
winds. Hail would be a secondary but non-zero threat given
somewhat elongated hodographs. Excessive rainfall potential
continues to diminish as better moisture return remains off to our
south. Regardless, airmass behind the front doesn`t look
anomalously juicy anyway. Storm motion looks fairly progressive as
well, so wouldn`t expect much in the way of training or
backbuilding.

Extended... 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. Return
flow from departing high pressure will result in decent instability
(~1,000 to 1,200 J/kg) coinciding with PWAT max of around 1.75"
Friday evening, so could get a stronger storm or two during this
time. Regardless, seems to be more consensus among ensembles this
time around. Though storm predictability is low this far out, ML
guidance continues to paint a broad 5 to 15% prob severe, so will
monitor in the coming days as additional details come into focus.

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
such, though there are chances for rain/storms in the forecast
this week, none are expected to be drought busting. 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 06Z TAF Issuance
Issued at 1026 PM CDT Mon Aug 17 2026

Mid clouds, bases around 7-8kft will start to filter into the region
tonight ahead an approaching cold front that is spurring on a few
clustered of showers and storms in far northwest WI and eastern MN.
As the front moves into central and north-central WI overnight
scattered showers are expected, mainly across northern WI. The risk
for thunderstorms will be decreasing as these showers move into
northern WI tonight, so have excluded TSRA from RHI for now. CAMs
generally show showers drying up early Tuesday morning as they move
to the east. However, a seasonally strong upper jet overspreading
the area Tuesday will reinvigorate the showers and storms late
Tuesday morning through the afternoon. Coverage of these
showers/storms should be scattered so went with PROB30 groups at all
TAF sites for portions of Tuesday.

Calm winds are expected before the front moves through overnight and
into Tuesday morning with winds veering back to the northwest with
gusts around 15-18kts.

&&

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

&&

$$

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