999
FXUS63 KGRB 050335
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1035 PM CDT Tue Jun 4 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Gusty southwest to west winds up to 35 mph are expected on
  Wednesday. Brief higher gusts in excess of 40 mph will be
  possible in any strong showers and storms in the afternoon and
  early evening.

- Conditions hazardous to small craft will be possible at times
  from Wednesday through Friday.

&&

.DISCUSSION...
Issued at 200 PM CDT Tue Jun 4 2024

Short Term...Tonight and Wednesday

Showers and thunderstorms will continue to develop through this
evening as instability builds across the region and the region
reaches its convective temperature. The best chance will be
across central and north- central Wisconsin where instability is
more robust; however, east- central and northeast Wisconsin could
also see activity as these areas continue to destabilize. SBCAPE
values have soared to around 3 J/g this afternoon; however, bulk
shear values are only 10 to 20 knots. Some of the stronger storms
could approach severe weather criteria, but most of the storms
should only produce heavy rain, gusty winds, and small hail.

A cold front will bring a line of showers and a few thunderstorms
through the area from west to east later tonight into Wednesday
morning. Instability by the time these storms roll through the
area should be fairly meager, with this activity expected to
remain below severe limits.

After the showers and storms exit the region Wednesday morning,
the rest of the morning should be dry. Another round of showers
and thunderstorms are expected Wednesday afternoon as a shortwave
tracks through the western Great Lakes region as modest
instability builds across the region. CAPE profiles are fairly
shallow, with the equilibrium level topping out at 16-19k ft and
an inverted V sounding near the surface. There isn`t much CAPE in
the hail growth zone given the shallow nature of the CAPE
profiles, with the HGZ in the very top of the sounding. Although
bulk shear soars to around 40 knots on Wednesday, effective bulk
shear is half of that at, around 20 knots, with SBCAPE values of
400 to 700 J/kg. Therefore, the strongest storms could produce
gusty winds with not much hail to speak of or pea size if any does
form.

Lows tonight will stay fairly warm; ranging from the middle to
upper 50s across north-central Wisconsin to the middle 60s across
the Fox Valley. Highs on Wednesday are expected to mainly be in
the middle to upper 70s, with a few 80 degree readings possible.
Most notable on Wednesday will be the lower dew points, as dew
points tumble into the 50s from west to east.

Long Term...Wednesday Night Through Tuesday

Behind a departing short-wave Wednesday night the dominate
feature of the extended period will be a cut-off low that is
forecast to stall out over the eastern Great Lakes/SE Ontario
through the beginning of next week.

Wednesday night through Thursday morning...Thunderstorms will
likely be on-going into the Wednesday night period as a fast
moving short-wave and attendant cold front move across the
region. Instability will be modest by this time with MUCAPEs
forecast to range from 500-700 J/kg, highest in north-central WI.
Deep- layer wind shear is expected to be decent with values
ranging form 40-45 kts, however, the effective shear looks to be
about half that with values forecast to range from 20- 25 kts.
Additionally, inverted-v soundings support a marginally severe-
wind threat with any storms that developed as winds at 850mb are
forecast to reach 30-40kt during this period. Any storms that do
develop may also produce small hail and heavy rain, however, given
the speed at which these storms are expected to be moving (east
around 30-35 kts) the flash flooding risk looks low, even given
PWATs around or slightly below 1". Thunderstorm activity should be
out of the region just after midnight Thursday morning.

Rest of the extended...Ensemble models have consistently been
showing a slow-moving trough dropping south out of central Canada
Thursday. This trough is then forecast to develop into a cut-off
low pressure system as it stalls out over the eastern Great
Lakes/SE Ontario. A round of showers and storms are expected
Thursday afternoon and evening as the trough initially moves
across the region, but rainfall amounts look light with most
locations seeing just a few hundreths up to a tench of an inch.
Areas near the UP boarder may see slightly higher amounts,
although the probability of greater than 0.25" is only 20-30%.
After that initial round of rain Thursday, framing out any
additional periods of precipitation Friday through Monday becomes
difficult as confidence is low with the details. In general,
expect periods of light on and off showers and storms Friday
through this weekend with generally party cloudy skies.

The cut-off low will stick the area in a northwest flow pattern
which will bring near to or just slightly below normal
temperatures Thursday through Monday with highs ranging form the
low 60s to middle 70s each day.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1034 PM CDT Tue Jun 4 2024

Showers and thunderstorms will become likely overnight as a cold
front approaches from the west. MVFR/IFR conditions will accompany
the thunderstorms. Surface wind gusts to 35 knots are possible
with some of the storms.

The activity will end from west to east Wednesday morning, with
clearing skies by midday. An upper level disturbance is expected
to produce scattered thunderstorms late Wednesday afternoon and
early evening. These thunderstorms will have high bases, with dry
air below. This could produce local strong downdrafts below the
cloud bases, and possible strong surface winds.

&&

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

&&

$$

DISCUSSION.....Kurimski/GK
AVIATION.......RDM