702 
FXUS63 KGRB 260802
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
302 AM CDT Wed Jul 26 2023

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 301 AM CDT Wed Jul 26 2023

Main forecast concerns center around convective trends this
morning and again on Thursday, as well as how warm to take
temperatures on Thursday.

The 07Z MSAS surface analysis showed weak high pressure over the
eastern Great Lakes, a weakening boundary over Upper MI and a warm
front that extended from the northern Plains into the Midwest. The
radar mosaic indicated several clusters of strong to severe
thunderstorms over much of the Upper MS Valley. Temperatures were
quite warm early this morning with readings in the lower 70s
across east-central WI.

One strong MCS over west-central WI is forecast to track east-
southeast across parts of central and east-central WI this
morning. Other weaker storms will move across other parts of
northeast WI as well. Despite a typical time when storms tend to
weaken, this MCS will still have morning MUCAPES around 1K J/KG
and 30-35 knots of bulk shear at its disposal. Anticipate strong
winds to be the primary threat as these storms roll through,
especially from Hwy 10 south. In addition to the wind threat, PW
values of 1.5 to 2.0 inches will support locally heavy downpours
with a potential of a quick 1-2 inches of rain. Once the MCS
departs with the mid-level shortwave trough, subsidence should
allow for some clearing to begin from west to east. Max
temperatures for today will range from near 80 degrees near Lake
MI, to the middle 80s over central WI.

Weak area of high pressure to move across WI tonight and at least
bring mostly clear to partly cloudy skies and light winds to
northeast WI. As an upper-level high pressure builds across the
central CONUS, upper heights rise over WI through the night.
Another ripple riding around the top of the upper high may bring
the next thunderstorm complex toward northern sections of the
Great Lakes after midnight. An increase in clouds over north-
central WI later tonight with the leading edge of showers/storms
approaching toward daybreak. In addition, anticipate fog to
develop overnight which may become locally dense at some
locations. Min temperatures for tonight to range from the upper
50s to lower 60s north, middle to upper 60s east-central WI.

This thunderstorm complex is progged to weaken as it moves across
northern WI Thursday morning. However, shower and thunderstorm
activity is forecast to pick up once again in the afternoon as a
cold front drops southeast into an unstable air mass. MUCAPES over
northern WI could reach 2K J/KG, mid-level lapse rates push 7.0
C/KM and bulk shear at around 30 knots. There are also hints at a
diffluent flow aloft. Expect to see the next round of
thunderstorms to develop by mid-afternoon and push across northern
and parts of central WI by late afternoon. SPC has placed all of
the forecast area under a marginal risk of severe storms that
would continue into Thursday night, so stay tuned. Thursday still
looks like the warmest day of the week with max temperatures in
the middle 80s near Lake MI, upper 80s to around 90 degrees north
and lower to middle 90s south. Heat indices appear to be only a
couple of degrees above the air temperature, thus do not
anticipate a need for any heat advisories at this time.
Nevertheless, precautions should be taken to prevent any heat
related illnesses.

.LONG TERM...Thursday Night Through Tuesday
Issued at 301 AM CDT Wed Jul 26 2023

Weather Summary...

 - Thunderstorm chances appear highest during the Thursday night
   through Friday night period though timing and severity remain
   uncertain. A severe threat may materialize at some point 
   during this period. Confidence is modestly higher for severe 
   potential on Thursday evening compared to Friday or Friday 
   night.

 - Potential for very warm temps will remain over central and
   east-central WI on Friday, though cloud cover and precip 
   chances lead to high spread in forecast temps.

 - High pressure will bring cooler and less humid air into the 
   region this weekend.


Thursday night through Friday night...Shortwave energy, moving east 
across Canada, will push a slow moving cold front south across the 
Upper Peninsula and northern WI on Thursday night. Instability is 
looking more impressive ahead of the boundary than last night, 
ranging from 1000-2000 j/kg.  While convergence along the front 
remains modest and upper support is lacking, the forcing should be 
sufficient for strong to severe thunderstorms to develop late in the 
afternoon into the evening hours.  Deep layer shear is higher north 
of the boundary, but above normal 700-500mb flow will lead to 30-35 
kts of deep layer shear that could lead to storm organization and a 
hail/wind threat.  A heavy rainfall signal is also present with 
cloud layer winds parallel to the boundary, but storms should be 
sagging south which will limit flooding potential somewhat.

The front will continue to slide south on Friday with models 
generally painting a picture of cloud cover and light precip at 
times through the day.  Severe parameters are more focused over the 
southern half of Wisconsin where better insolation will be present, 
but central and east-central WI will be on the northern fringe of 
the higher instability.  Looks like a conditional severe threat 
shaping up pending upon cloud cover and precip.  Rain chances will 
then diminish on Friday night from north to south.

Rest of the forecast...Canadian high pressure will build in behind 
the front for the weekend.  Cooler and less humid air will offer a 
reprieve from the very warm conditions.  Precip chances will 
increase again early next week when warmer air will try to surge 
into the region once again.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1032 PM CDT Tue Jul 25 2023

An upper level disturbance is expected to produce a an area of 
thunderstorms as it moves across Minnesota tonight and Wisconsin 
Wednesday morning. It will likely be accompanied with MVFR 
ceilings and periods of IFR conditions. Wind gusts to 35 knots are
possible Wednesday morning at the leading edge of the 
thunderstorms. The showers and thunderstorms should exit the area 
during the afternoon, with improving flying conditions. Clearing 
skies are expected Wednesday night, but areas of dense ground fog 
could form towards daybreak Thursday. 

.OSH...VFR conditions are expected overnight. A thunderstorm
complex is expected to arrive Wednesday morning and bring showers
and thunderstorms and MVFR conditions. IFR conditions are possible
for a few hours. Winds may gust to 35 knots along the leading 
edge of the thunderstorms. Conditions will improve Wednesday 
afternoon, with VFR conditions likely by evening. Areas of dense 
ground fog are possible around daybreak Thursday.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......MPC
AVIATION.......RDM