676
FXUS63 KGRB 150921
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
421 AM CDT Mon Jul 15 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Isolated to scattered storms expected this afternoon and
  evening. Some storms could be severe. Primary hazards are
  damaging winds and hail.

- Heat index values in the upper 80s to middle 90s across central
  and east central WI.

- Mainly dry weather expected mid-late week into next weekend.
  Temps drop below normal Wednesday, but will be around normal
  rest of the time.

&&

.DISCUSSION...
Issued at 421 AM CDT Mon Jul 15 2024

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

Main forecast concerns will be determining shower/storm potential
today and if the severe weather risk. Last day of the heat and
humidity with max heat indices in the mid 80s to mid 90s. Some
possible dense fog and smoke impacts as well.

Convective Trends & Severe Wx/Flooding Chances:

A dry start to the day is on tap for the area as one large MCS
tracks into MI and the OH Valley and another one pushes across
MN. Quite a bit of debris clouds from the MCS to our west is
expected, which will likely limit surface heating for a time this
morning (and if the HRRR is right could bring a few sprinkles this
far east), with additional clouds developing later in the day
possibly further holding down instability. This, along with the
exact placement of each shortwave, will lead to some uncertainty
on how this afternoon will play out. The more organized severe
weather event (an eventual MCS) is forecast to be to our south
with the southern shortwave/outflow boundary, but severe storms
will still be possible in our area after 18z ahead of the cold
front and lake breeze dropping south, as bulk/effective shear
increases to 30-50 kts and lapse rates increase, supporting the
wind/hail threats. There is still some uncertainty how widespread
the storms will be, as just how unstable we will get and if some
dry air and capping will inhibit storm development. CAMs in decent
agreement (especially compared to previous days/events) showing
isolated to scattered activity in the afternoon and early evening,
with some bowing segments as the event unfolds. So expecting at
least isolated coverage. Moisture will be a concern over the far
north as dewpoints may not get into the mid 60s. Inverted-V
soundings will support winds being transported to the surface.
The tornado threat is very low, with LCL heights over 1000 ft and
questions regarding instability and low level moisture. But the
tornado chance peaks in central WI in the mid to late afternoon
when LCL heights slightly lower and SRH maxes out, and if any
discrete cells can form and become well organized. SPC has kept
most of the area in a marginal risk for severe weather, with the
slight clipping the southern counties.

With the isolated/scattered nature of the storm activity, the
overall flood threat will be low/reduced. Plus, most of the
activity looks to have decent forward speed. However, favorable
heavy rain environment with PWATs around 1.5" would support
heavy rain producers. If any storms that can align and move over
the same location, it could bring a flooding threat, especially in
areas that saw recent heavy rain (specifically parts of the Fox
Valley where 1-hour flash flood guidance remains around one inch).

While most of Tuesday is looking dry, models hinting at some
isolated shower activity in the mid morning through mid afternoon
as a weak front crosses the area and an upper trough drops in the
Great Lakes. GFS is advertising stronger cold front pushing, with
more widespread shower activity. Suspect we might need to increase
PoPs during the day.

Heat & Humidity:

One more day of warm and humid conditions today. Will stick close
to the best performing guidance from yesterday (BCONSALL) which
has highs in the 80s for most of the area. Could get a 90 if we
get a little more sun than expected in/just west of the Fox Valley
as 925mb temps support low 90s. A little relief is expected near
the shores of Lake Michigan as onshore winds are expected this
afternoon. Dewpoints off to a higher start compared to the
previous mornings with low to mid 70s across much of central and
east central WI. These look to remain in place for most of the
day, producing heat index values in the low to mid 90s. Drier air
will arrive in tonight. with CAA will ushering in cooler air for
Tuesday with highs in the 70s across north-central WI and in the
low 80s over the south.

Fog / Smoke Trends:

With clear skies, light winds, a steep low-level inversion,
dewpoints in the 60s to mid 70s and recent rains, fog developed
across much of the area overnight, mainly across central and
northern WI. The patchy fog, locally dense, should continue to
expand through around sunrise then will lift/burn off. Can`t rule
out a little patchy fog late tonight into Tuesday morning, but
stronger winds just off the surface and slowly lowering dewpoints
should limit fog formation. Still no fog on Lake Michigan, but
will continue to monitor as winds turn south this morning and the
highest dewpoints arrive with water temps still in the 60s.
Northern buoy is reported 68/68 so would imagine we are not far
away from some fog forming...just need a little more moisture.

In between the areas of convection across northern and southern
WI yesterday, GOES GeoColor showed areas of wildfire smoke across
Lake Superior, Upper MI and WI. HRRR/RAP showing the smoke, some
near or at the surface, continuing across Lake Superior, Upper MI
and northern/eastern WI. Have added some haze to the sky grids
today to account for this. A separate area of mainly elevated
smoke will approach from the west through the day and spread
across the region into Tuesday. Could have some air quality issues
at times, along with possibly some visibility reductions if the
thicker/lower smoke makes it here.

Long Term...Tuesday Night Through Sunday

The upper pattern will shift in the extended, bringing a broad
upper ridge just west of Wisconsin, extending over most of
western and central CONUS. This will set up a period of strong
northwesterly flow for our region, bringing in drier and cooler
conditions for the middle of the week through early next weekend.
This is not to say we will be completely dry, as a few shortwaves
may yet bring some isolated to scattered convection, but no
widespread rainfall or severe weather is anticipated. High
temperatures during this time will drop into the 70s for Wednesday
before gradually moderating back towards the upper 70s to middle
80s by next weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1037 PM CDT Sun Jul 14 2024

Mainly dry conditions are expected through Monday morning. Models
continue to show elevated smoke across the region as well, enough
to create hazy conditions. Winds should be light and variable
tonight, then increase to 10 to 15 knots from the southwest Monday
afternoon. Some ground fog will be possible early Monday morning
given light winds, recent rainfall, and a low- level inversion.
Will continue to monitor for potentially dense fog on Lake
Michigan through Monday morning given water temperatures in the
low to mid 60s. Showers could then track through the area Monday
afternoon and evening across northern Wisconsin along with some
thunderstorms as a cold front sweeps through the region.
Confidence in this activity is currently low enough to leave out
thunderstorms, but will keep the showers in for Monday afternoon
and evening. Despite the activity, conditions are expected to
remain VFR.

&&

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

&&

$$

DISCUSSION.....Bersch/Uhlmann
AVIATION.......Kurimski