442
FXUS63 KGRB 141557 AAA
AFDGRB

Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
Issued by National Weather Service Milwaukee/Sullivan WI
1057 AM CDT Wed May 14 2025

.KEY MESSAGES...

- Marine Dense Fog Advisory for the nearshore areas of Lake
  Michigan through Thursday.

- There is a chance (25-40%) for thunderstorms this afternoon
  for central WI with small hail possible.

- Showers and storms are most likely (50-80% chance) Thursday
  afternoon and evening. Some severe storms are likely with the
  passage of a cold front. All hazards possible over central WI
  and large hail possible over eastern WI.

&&

.DISCUSSION...

UPDATE...Issued at 1057 AM CDT Wed May 14 2025

The fog quickly dissipated this morning and there is now a large
area of clear skies. The clouds are bubbling over central WI
where there is a little bit of mid level vorticity. The
northwest half of WI is in a more favorable position for
diurnally driven thunderstorms this afternoon due to that weak
vorticity, which includes the western fringe of our forecast
area (Eagle River to Stevens Point and west). The shear is very
weak, so it only looks like a small hail threat. However, most
of the area west of the Fox Valley should become fairly unstable
due to the sunshine, so showers (lower chance for thunder due to
no shear) are possible for most areas this afternoon.

Expecting another round of dense fog tonight, although it should
remain more confined to lakeshore counties and the Fox Valley
rather than surging all the way into central WI.

Cronce

Issued at 418 AM CDT Wed May 14 2025

Dense fog of 1/2 mile visibility or less has pushed inland from
Lake Michigan but has also begun to develop inland as well.
Dense fog was originally tracked from the lake but has begin to
develop elsewhere further inland than originally expected. A
Dense Fog Advisory is in effect for Marinette, Oconto,
Menominee, Shawano, Waupaca, Winnebago Counties and east through
10 AM CDT Wednesday. The visibilities have largely started to
fall across the CWA with low ceilings mixing in as well. There
has not been much signal for how this will play out early this
morning but given the worsening conditions I have continued to
spread the Dense Fog Advisory further west as obs continue to
show lower visibilities. It does seem to have a patchy nature
to it as some locations are showing up and down visibilities.
However, later this morning as the sun rises we will start to
see the fog and low clouds dissipate as we warm up. Advisory is
slated to end at 15z be may be able to be ended earlier
depending on how quickly this dissipates.

Another round of pop-up showers and storms is possible this
afternoon, primarily toward central WI away from the lake due to
more stable air. Surface based CAPE increases to 500 to 1000
J/kg from central to north- central WI but with basically no
deep layer shear any storms will remain unorganized. There is
not much out there to force storms at all either outside of just
your typical diurnal heating and maybe a some weak PVA aloft but
if we can get a few storms the outflows from dying storms may
be enough to bring more scattered storm activity. Once the sun
goes down activity will likely dissipate fairly quickly

Into Thursday we may see a fairly significant severe weather
setup for the region as an EML will be building into Wisconsin
starting Thursday morning, as a warm front surges north across
the region. This will keep us capped in the morning hours but
will feature steep 700-500mb lapse rates around 7.5-8.5 deg
C/km. The cap will be located around 800-700mb and will be
fairly significant at first. A few showers/storms may be
ongoing along the leading edge of the EML early Thursday, mainly
across the northern portions of the state, but for the most
part the strong cap should limit shower/thunderstorm activity
through at least early afternoon. The latest CAMs generally show
little to no activity Thursday morning, which will mean plenty
of sun to warm things up ahead into the afternoon. At the
surface, southeast winds will allow for warmer temps away from
the lake, with upper 70s to low 80s over the central and
northern portions of the state. Expect cooler temperatures
closer to the lake. Surface dewpoints are expected to rise into
the upper 50s to mid 60s, highest further south. This is
expected to result in a large band of 2000+ J/KG of MLCAPE
across much of the state by early afternoon, gradually sliding
eastward.

An upper low centered over South Dakota will swing a band of
PVA into western WI into the afternoon hours. In addition,
a cold front at the surface will be swinging through as well.
Thus, the forcing is expected to be plentiful and will help with
overcoming the capping inversion from the EML. We will also
start to see increasing flow aloft overspreading the area from
the west, resulting in 40-50 kt of deep layer shear across the
region. The greatest uncertainty with the forecast remains the
dry midlevel air due to the EML. Most models have storms at
this point especially across northern WI with the capping
inversion largely eroded by the mid afternoon. Even if we do not
fully erode the cap the forcing is still enough to bring some
elevated supercells with large hail. But if we can become
surface based the concern for all hazards increases. The
question then turns to what the mode will be.

Initially discrete supercells may be likely and while it could
get a bit messy (less-discrete) fairly quickly you could easily
see this remain mostly individual cells. The NAM 3km is very
much a model that trends toward producing a line of storms but
even this model keeps things rather discrete and cellular in
nature. Eventually it may become more linear later on but this
is definitely something to note. Any individual cells will have
access to great low level helicity profiles with very large hail
and even some tornadoes (possibly strong) will be possible. One
thing to note is that further north cells become less fully
discrete which could cause storms to injest rain-cooled air
around it but this also could be a positive if it helps lower
the LCLs which may be somewhat high with this event. Since
frontal and upper level forcing will be stronger across the
northern half of the state it remains likely that at some point
these storms will become more linear in mode. The risk for
straight line winds will increase with any linear segments,
along with a continued hail and a QLCS tornado risk.

As this pushes east the lake will come into play again with
southeast flow and lake breeze circulation potentially causing
storms to go elevated. Storms are likely to move quicker than
expected with most of the severe risk out of the area by the
early to mid evening hours.

Friday through Wednesday:

Upper level trough pivots across the western Great Lakes on Friday
with another shortwave crossing during peak heating ahead of
secondary cold front. The forcing and surge of CAPE over 500J/kg
may result in another round of showers and some thunderstorms
especially over east-central WI in the afternoon. Soundings show
well mixed boundary layer with inverted-V profile, so there is
a potential for strong and gusty winds with stronger storms.
Really though, even besides possible convection, it will be a
warm and breezy day as 850mb winds of 40-50 kts support peak
gusts of 35-45 mph in the afternoon, strongest from the Fox
Valley to the lakeshore. Highs will reach around 80 east-central
and well into the 70s elsewhere.

Cold front sweeps through Friday night as low pressure tracks
across LakeSuperior. Cooler temps, arrive for Saturday as highs
range from the mid 50s north, to around 60 in central WI and
into the mid 60s for the Fox Valley to the lakeshore. Still
could be scattered showers over northern WI in the cold air
behind the low.

High pressure then settles from Manitoba to Ontario later in the
weekend bringing dry weather. Temps could drop into the mid 30s
north Saturday night and/or Sunday night. NBM probabilities of
min temps less than 35 are around 40 percent Saturday night over
Vilas County, but increase and expand to 40-65 percent on
Sunday night over much of northern Wisconsin. If winds become
light, some frost could occur one or both of these nights.

Broad troughing over the western CONUS late this weekend shifts
east early next week, bringing the next chance of showers and
storms to the area Monday night into Tuesday. Early, but machine
learning progs do show at least a small chance (5-15%) that
stronger storms could occur.

Kuroski

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...

UPDATE... Issued at 1057 AM CDT Wed May 14 2025

The fog and low clouds cleared quickly this morning. Diurnal
cumulus clouds are developing, with more agitated cu toward
central WI. Centra WI has the better chance for scattered
thunderstorms this afternoon, including the possibility for
small hail. Other areas west of the Fox Valley have a chance for
showers and lower chance for lightning.

It looks like a rinse and repeat situation for fog and low
clouds again tonight. Although the dense fog smay remain more
confined to lakeshore areas rather than surging all the way into
central WI.

Cronce

Issued at 626 AM CDT Wed May 14 2025

Fog remains scattered across northern WI with the denser fog
more so patchy across the area. In addition this somewhat
follows with the VLIFR CIGS. Gradually with the sun coming out
we expect to see fog and even the low CIGS break up and
eventually clear out later this morning across the area with
some spots being quicker than others. VFR conditions later today
though there will be chances for a few weak storms though they
will mostly be located further west toward central WI. Into
tonight we will again see chances for fog, possibly dense and
low CIGS to push in from the lake. It looks likely to be less
widespread than this morning but should at least impact areas
closer to the Lake/Bay.

Kuroski

&&

.MARINE...
Issued at 1057 AM CDT Wed May 14 2025

Given that the enviroment will continue to remain favorable
(moist air over the cool open waters) for dense fog until this
pattern breaks, we extended the Marine Dense Fog advisory until
7PM Thursday. We may be able to expire that a little earlier on
Thursday as southerly winds kick in, so there is uncertainty in
the end time. This includes the Bay area, although we may see
less foggy conditions during the daylight hours there.

Cronce

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until noon CDT today for WIZ022.
MARINE...Dense Fog Advisory until 7 PM CDT Thursday for LMZ521-522-
     541>543.

&&

$$

DISCUSSION...
AVIATION...
MARINE...