755
FXUS63 KGRB 142314
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
614 PM CDT Sun Jul 14 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Small chance (less than 20%) that northern end of storm complex
   could impact the southern Fox Valley this evening. Gusty winds
   and locally heavy rain will be the primary threats.

 - One or two rounds of strong to severe storms are possible
   Monday into Monday evening as a strong cold front crosses the
   region. Slight risk of severe (level 2/5) for areas south of a
   line from Wausau to Green Bay. Primary hazard with stronger
   storms is damaging winds, although hail and an isolated tornado
   cannot be ruled out with any discrete cells.

 - Heat index values in the low to mid 90s on Monday from the Fox
   Valley to the lakeshore.

 - 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 246 PM CDT Sun Jul 14 2024

Short Term...Tonight and Monday

Focus for the short-term continues to revolve around severe
weather potential, mainly for tomorrow. However, there are still
some questions with storm evolution this afternoon and evening.
Some strong to severe storms may be possible along and south of
the Highway 10 corridor, although forecast confidence remains on
the low end due to the recent mishandling of CAMs in regard to
MCS activity.

Convective trends... As remnant showers/storms exited to the
southeast throughout the morning, attention then turns to a
storm complex that several CAMs are advertising across southern
Wisconsin this evening. Convection looks to ride in along a weak
shortwave this afternoon before really igniting during the
evening. Biggest concern will be whether or not the northern edge
of this MCS makes it up into our southern counties that are
currently vulnerable to flash flooding due to recent heavy rain
and ongoing flooding from previous convection. However, there is
evidence to suggest that most of the action will stay to our
south. Confluent mid-level flow will set up a convergent zone
across southern Wisconsin as moderate warm air advection and moist
inflow maximize instability (3,000+ J/kg CAPE) during peak
heating. However, any slight shift northward would be problematic
for the southern Fox Valley where 1-hour flash flood guidance has
lowered to less than one inch. Definitely warrants keeping an eye
on, especially given the recent history of CAM underperformance.
Additional shower/storm activity will then be possible across the
north later this afternoon where northwest flow off of Lake
Superior may be enough to generate some pulse storms.

Monday severe weather potential... To no surprise, CAMs still
showing several different scenarios that could unfold tomorrow.
Several models (ARW and FV3) are showing a more wind-driven,
bow echo-type solution given favorable deep layer shear of 50+
knots. This would likely result in a widespread damaging wind
threat, depending on how convection earlier in the day behaves and
where the bow echo develops later in the afternoon. This being
said, increasing low-level SRH out ahead of the cold front would
introduce the possibility for some discrete cells to pop up during
peak heating. If any mature cells were to develop and tap into
abundant low-level moisture, instability, and SRH, rotating storms
capable of producing tornadoes would be within the realm of
possibility. This scenario would likely result from a quicker exit
to convection earlier in the morning, allowing for a longer
recovery time for instability to build back up and convective
ingredients to organize. In this case, isolated damaging winds,
hail, and localized flooding would be the main threats.
Regardless, will be hard to pin down storm mode for tomorrow until
the first round of storms moves through tomorrow morning.

Fog/smoke... RAP/HRRR guidance continues to show wildfire smoke
being a concern through the beginning of the week. A plume of
thick near surface smoke will make its way across the US/Canada
border and spread over Lake Superior tonight through tomorrow
morning, potentially making its way into northern Wisconsin.
Visibility and health concerns would likely come into play during
this time, especially with the combined influence of elevated
smoke from western CONUS wildfires.

Fog once again seems likely tomorrow morning given light winds,
recent rainfall, and a low-level inversion trapping moisture near
the surface. Unsure where exactly it will develop, so opted to
retain patchy fog across most of the forecast area. Will continue
to monitor for potentially dense lake fog tomorrow morning with
sustained water temperatures in the mid 60s and increasing
dewpoints.

Long Term...Monday Night Through Sunday

Storms along and just ahead of cold front shift east across the
lakeshore zones and quickly on the east Monday evening. Given the
extent of effective shear/helicity and instability along and
ahead of the front, storms even first thing in the evening could
be severe. Drying out late Monday night as subsidence and dry air
build in in wake of the strong shortwave and cold front. Next
chance of some showers arrives late Tuesday night or more so
Wednesday as southern edge of sharp mid-level trough crosses the
upper Great Lakes. Just low-end chance pops now, but probably
will be some scattered showers and isolated thunderstorm during
peak heating on Wednesday. Highs on Wednesday will be on the
cooler side of normal, with readings not cracking 70 over northern
WI while reaching the mid 70s for the rest of the area. This could
be followed up with some chilly min temps in the 40s on Wednesday
night over the north.

Broad and large area of seasonably strong high pressure expanding
from south central Canada to the northern Plains may finally bring
what many have been looking forward to for a long while in our
region; a multi day period of dry weather. Looks like the time
frame favored would be from Thursday through Saturday. Sure looks
like that right now, but we have thought that before, so we`ll
cautiously wait and see and enjoy it if it indeed comes to fruition.
Temperatures will be rising back to around normal these days with
80 north and low to mid 80s for the rest of the area. A reinforcing
trough and cold front could bring another chance of showers back to
the region later next weekend.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 614 PM CDT Sun Jul 14 2024

Mainly dry conditions are expected through tonight. However, a
stray shower or storm may make it up into the southern Fox Valley
this evening, mainly affecting ATW and MTW. Storms are also
expected across the far north, but should stay north of RHI.
Storm activity would likely remain elevated, so expect mainly VFR
conditions. Models continue to show elevated smoke across the
region as well, enough to create hazy conditions. Winds should
be light and variable tonight. 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 tomorrow morning given water
temperatures in the low to mid 60s. Showers could then track
through the area Monday afternoon across northern Wisconsin along
with some thunderstorms. Confidence in this activity is currently
low enough to leave out thunderstorms, but will include showers in
this set of TAFs for the afternoon. Despite the activity
conditions are expected to remain VFR.

&&

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

&&

$$

DISCUSSION.....Goodin/JLA
AVIATION.......Kurimski