094
FXUS63 KGRB 110920
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
420 AM CDT Thu Jul 11 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Small chances (30% or less) for showers and storms this
  afternoon/evening this afternoon and Friday. Severe weather not
  expected low, but storms could produce locally heavy downpours.

- Warmer and more humid conditions arrive this weekend through
  early next week. Heat index values in the 90s are expected over
  central, east central and parts of far NE WI Sunday into Monday.
  Heat indices could approach advisory criteria over the southern
  CWA on Sunday, unless thunderstorm development occurs.

- Increasing moisture and instability, combined with a couple
  short-waves and cold frontal passages, could lead to a few
  rounds of strong to severe storms this weekend into early next
  week.

&&

.DISCUSSION...
Issued at 418 AM CDT Thu Jul 11 2024

Short Term...Today...Tonight...and Friday

Main forecast concerns will be where to include small shower/storm
chances, fog potential and cloud trends.

Shower/Storm Chances & Cloud Trends:

Dry conditions are expected to start the day, with some low clouds
and fog over the north and mid and high clouds over the south. The
mid and high clouds will linger over the south into the late
morning and early afternoon, with the low clouds over the north
mixing out this morning. The more widespread shower/storm activity
will be well to our south today, closer to the stronger shortwave
energy and deeper moisture. But a weaker piece of shortwave
energy will track across the area today within the broad upper
level trough over the region. Combined with daytime heating
producing SBCAPEs up to 1000 J/kg, isolated showers and storms
will again be possible, mainly over the southern CWA. The Lake
Michigan lake breeze could also help kick off or enhance any
activity. Severe weather is not expected, but a brief heavy
downpours is possible (PWATs around an inch). Soundings showing an
inverted-V, but just not much wind to mix into. Any wind would
have to come for a storm that can pulse up and generate some brief
wind of its own (microburst). Any shower/storm activity will
decrease in the late afternoon and evening as instability weakens
and the focus shifts south. Further north, the influence of the
weak surface high pressure, less moisture and a weak cap looks to
keep things dry. But can`t rule out a sprinkle or a shower near
the MI border along the Lake Superior lake breeze. A lingering/
stray shower is possible tonight, but expect most/all will stay
dry. Models advertising another weak shortwave on Friday that
could touch off an isolated shower or possible storm. But some
uncertainty if the boundary layer will be a little too dry and if
the cap will hold down any activity.

Fog Potential & Temps:

Fog is trying to expand and thicken across parts of central and
northern WI, just north of the thicker mid/high clouds, but it
seems to be struggling so far. There should be some expansion of
the fog through sunrise across central and northern WI, then it
will lift/burn off through mid-morning. Fog will be possible
again tonight as winds will remain light, skies will be mostly
clear and another sharp low-level inversion setting up. Will
carry some patchy fog overnight into early Friday, mainly
northwest of the Fox Valley where the HREF and SREF are
highlighting the best chances.

Temps will be at or slightly above normal today into Friday, with
highs mainly in the low to mid 80s and lows in the 50s across the
north and in the lower half of the 60s across most of central WI
and the Fox Valley. Temps near Lake Michigan will remain slightly
cooler. Dewpoints in the low 60s will keep a touch of humidity in
the air across the Fox Valley, but the Northwoods looks to mix out
today with dewpoints in the 50s, possibly some 40s in the sandy
soil areas. Heat indices should remain in the 80s on Friday as we
ease into a period of higher heat and humidity.

Long Term...Friday Night Through Wednesday

The main concerns in the extended will be the growing storm
concern for the weekend and early next week as warm and moist
airmass moves into the region.

Heat...A warmer and more moist airmass will push into the
western Great Lakes Friday night through Saturday. This will bring
daytime high temperatures well into the 80s by Saturday and keep
them there Sunday and Monday as well. Depending on active weather,
portions of the area may even hit the low 90s. At the same time,
dewpoints will be on the increase by Saturday, pushing into the
middle to upper 60s and low 70s by Saturday night. Suffice to say
it will be hot. Whether we get to heat advisory remains in low
confidence, as precipitation may disrupt the better heating, but
the best chance will still be on Sunday.

The heat will depart towards the middle of next week after a cold
front crosses the region early in the week.

Precipitation...

The influx of warmth and moisture will also generate ample
instability in the region each afternoon Saturday through Monday.
Each day will see a chance for storms, but there is plenty of
uncertainty in terms of timing and strength.

Saturday...Saturday appears to have the weakest capping in place,
so some isolated convection will be possible in the afternoon.
The better threat will be later in the day however, as a shortwave
crosses the better instability axis to our west. Any storms that
form there may organize and come west late Saturday, crossing the
region in the early to mid overnight hours. Bulk shear Saturday is
still modest, around 20 to 30 knots but mid-level lapse rates
will be decent around 7-8 C/km. This modest upper support coupled
with the low level instability would support at least isolated
severe wind and hail Saturday and Saturday night.

Sunday...The first challenge for Sunday will be resolving any
potential active weather from Saturday, which could stabilize the
region a bit, especially further north. Sunday also has much
stronger capping in the mid-levels, which may further inhibit any
storm development, at least for the afternoon. Finally, a
shortwave crosses sometime late Sunday, which may be sufficient to
break the cap, especially as bulk shear values quickly increase
over the course of the day. If storms form, would currently place
the best bet to be across central to southern WI, where the
instability axis is at its greatest.

Monday...Finally, a cold front is expected early next week, which
will serve as the next chance for organizing precipitation in the
area. If this occurs in the late afternoon and evening, this would
favor another round of strong to severe storms across the region.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 939 PM CDT Wed Jul 10 2024

Mostly clear skies are expected tonight. Some ground fog is possible
late tonight mainly north of a RRL to IMT line. Any fog that forms
should dissipate by 13z Thursday. Mostly sunny skies are forecast
Thursday, with isolated showers possible in the afternoon.

&&

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

&&

$$

DISCUSSION.....Bersch/Uhlmann
AVIATION.......RDM