042
FXUS63 KGRB 241749
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1249 PM CDT Mon Jun 24 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

 - A severe thunderstorm complex could produce damaging winds as
   it moves from northwest Wisconsin this evening to Lake
   Winnebago late tonight.

 - Conditions hazardous to small craft are possible late tonight
   and Tuesday morning along Lake Michigan.

 - Some rivers and streams will remain above bankfull into the
   middle of the week.

&&

.DISCUSSION...
Issued at 405 AM CDT Mon Jun 24 2024

Short Term...Today...Tonight...and Tuesday

Patchy ground fog should dissipate shortly after sunrise. Mostly
sunny skies and warm temperatures are expected today, with
increasing high clouds during the day.

A shortwave trough moving across Wisconsin will create upper
diffluent flow, while a strong jet at 850mb brings up warmth and
moisture. The combination of these should produce a thunderstorm
complex that could move from northwest WIsconsin this evening to
Lake Winnebago shortly after midnight. This would produce a path
of damaging winds if it does materialize. If an organized complex
does not occur, there will still be a broken line of storms that
could produce large hail and damaging winds.

The activity should exit the forecast area by daybreak Tuesday,
with clearing skies and warm temperatures by afternoon. West winds
downsloping across eastern Wisconsin should produce temperatures
in the middle to upper 80s, even at the bay and Lake Michigan
beaches.

Long Term...Tuesday Night Through Sunday

Primary period of focus for the extend forecast is Friday into
Saturday morning as a slug of gulf moisture surges into the
region ahead of an approaching low. Otherwise, mostly dry and
cooler temperatures are forecast for the middle of this week.

Tuesday night through Thursday...With an upper-level short-wave
departing the region and a ridge of high pressure building in
behind dry conditions are expected for the middle of this week.
Northerly winds Wednesday will usher in seasonally cool
temperatures with highs on Wednesday forecast to reach the middle
60s to low 70s, and overnight lows into Thursday dropping into
the middle 40s to low 50s.

Friday through Saturday...Ensembles are in general agreement that
rain will return to the region Friday as an area of isentropic
ascent over spreads the region. Periods of moderate to heavy rain
do look possible as forecast sounding show deep layer saturation
and PWAT values reaching 1.75-2.00 inches which is around the
90th percentile of climatology. Probabilistic guidance has a 35-
50% chance for greater than 0.5 inches of rain during this
period. With several area rivers expected to still be at or near
bankfull there are some minor flooding concerns. The potential
for stronger thunderstorms during this period is still unclear.
Models are showing increasing instability Friday night into
Saturday morning ahead of a trailing cold front which could
initiate scattered thunderstorms, but it`s unclear if these
storms will develop in an environment capable of producing severe
hazards.

Rest of the extended...Another cool start to the day Sunday with
early morning lows in the middle 40 to middle 50s as winds become
northerly. A building ridge should keep the remainder of the
weekend and the start of next week dry. There are some signs
anther system will traverse the northern CONUS during the middle
of next week which would keep the wet start to summer going into
July.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1249 PM CDT Mon Jun 24 2024

VFR conditions will prevail for the afternoon and most of the
evening hours before attention turns to a line of storms expected
for the late evening and overnight hours.

Storms tonight will form over Minnesota and western Wisconsin and
move east rapidly overnight. Arrival is expected in central WI
shortly after midnight and will rapidly progress eastwards. Storms
can produce damaging winds, especially in central WI and may also
briefly bring some large hail. The main uncertainty in the
forecast is whether any isolated activity develops ahead of the
main thunderstorm line, so made a mention of this in the 03Z
timeframe for AUW, CWA, and RHI. Any storm activity will end by
daybreak on Tuesday, with clearing skies expected to return not
too shortly after.

&&

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

&&

$$

DISCUSSION.....RDM/GK
AVIATION.......Uhlmann