915
FXUS63 KGRB 030847
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
347 AM CDT Wed Jul 3 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Some rivers and streams over portions of east central Wisconsin
  will continue to run above bankfull due to the heavy rain that
  occurred on Tuesday evening.

- Rain/storm chances will arrive from the west Thursday afternoon,
  becoming more widespread overnight. This has the potential to
  impact fireworks displays the night of the 4th, especially
  across central and north-central Wisconsin.

- On and off chances for rain/storms continue through early next
  week as upper-level flow remains unsettled.

&&

.DISCUSSION...
Issued at 347 AM CDT Wed Jul 3 2024

Short Term...Today...Tonight...and Thursday

Today and tonight...Most showers have exited northeast WI early
this morning. Main impact left from the heavy rain that occurred
on Tuesday evening (2-3 inches of rain in last 24 hours in good
portion of Winnebago and Calumet counties) will be smaller rivers
and streams running above bankfull before slowly dropping this
afternoon and tonight. Fog early that is most dense over central
WI will fade by daybreak as dry air aloft moves across and winds
shift more westerly. Expect a much warmer day across the board
with highs well into the 80s. Forecast soundings and MOS guidance
signal breezy winds developing early to mid afternoon with gusts
reaching 30 mph at times over central WI.

No big changes from previous forecast in terms of rain chances
today. Still a small chance of pop-up showers this afternoon into
early evening. CAMS are quite spotty in coverage, but all show
some hint at some showers due to lower convective temps (75-78F)
being achieved rather easily along with steeper low-level lapse
rates and sfc dewpoints still mainly in the 60s giving at least
500J/kg of MLCAPE. Though a rumble of thunder could occur, very
low chance, so just went with the shower mention. Rest of tonight
looks quiet with min temps as low as mid 50s north and as warm as
mid 60s for Fox Valley to the lakeshore.

4th of July...The holiday starts out dry but then becomes more
unsettled as the day progresses. Main culprit is shortwave trough
tracking from the plains to the upper mississippi valley by late
in the day. Small chance of showers through midday from the
southwest as elevated instability will be shifting toward WI and
warm/moist advection will be increasing even as low-level jet
remains tame. As we have seen multiple times, sometimes these
elevated showers will outpace the greater instability and expand
farther east than you expect. That could happen again during the
morning as some models show. At the least, should see thickening
clouds (highs will still touch the lower 80s for most locations)
but again could also see some light elevated showers from this
regime. Better chances for showers and possible rumbles of thunder
on track for the afternoon, again spreading in from the southwest
as shortwave trough draws closer and a warm front works into
southwest WI. Chances for rain will start to eclipse 55-60 percent
after 4-5 pm west of a line from Wausau to Waupaca to Wautoma
with chances increasing further from west to east as we work into
the evening of the 4th. SPC does have our far southwest CWA within
a marginal risk for severe, but at this point even though MLCAPES
will be near 1000J/kg, strongest low- level and mid- level winds
(effective shear) stay well to the southwest across IA, so think
the severe risk over central WI will stay on the lower side.

Long Term...Thursday Night Through Tuesday

Focus for the extended will be on rain/storm chances the evening
of the 4th as a robust shortwave drags a surface low across the
northern Plains. Rain is expected to arrive from the west Thursday
afternoon before becoming more widespread overnight, potentially
impacting fireworks displays especially across central and north-
central Wisconsin. An unsettled pattern containing several
shortwaves and accompanying chances for rain will then remain in
place through early next week.

Thursday evening through Saturday rain/storm chances... Closed
upper-level energy will dig across the northern Plains mid-week
before spinning up a surface low over the upper Mississippi Valley
Thursday evening. Warm air advection precip will then spread west
to east Thursday evening through Friday morning, bringing
additional chances for heavy rain to the forecast area. Current
ensemble guidance shows a 30 to 50 percent signal for exceeding 1
inch of rainfall in central Wisconsin through Friday evening.
While storm potential doesn`t look too impressive, cannot rule
out some rumbles of thunder given modest instability (700 to 900
J/kg) Thursday evening. This being said, better storm potential
looks to be Saturday afternoon with wrap-around shower activity as
the surface low departs to the east. Coverage will likely be
spotty given the absence of any surface features, although
surface dewpoints in the mid 60s and resultant CAPEs nearing 1,500
J/kg may be enough to generate some thunderstorms during peak
heating.

Rest of the extended... On and off chances for showers will
continue through early next week as agitated mid-level flow
persists. After dropping into the mid 60s to low 70s following
Friday`s precip, temperatures will then rebound heading into the
weekend before plateauing in the upper 70s to low 80s to start the
week. Expect temperatures during this time to run right around
average for this time of year.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1001 PM CDT Tue Jul 2 2024

Showers will taper off from west to east overnight, with dry
conditions expected Wednesday into Wednesday night. LLWS will
continue for the first couple hours of the TAF period at MTW,
then end.

Widespread IFR/LIFR ceilings will continue overnight. Increasing
west winds could cause ceilings to rise slightly around daybreak,
followed by a clearing trend early Wednesday morning. Gusty west
winds will occur during the day on Wednesday, and scattered
cumulus clouds are expected to develop. There is a small chance of
afternoon showers, but confidence is not high enough to mention
in the TAFs.

&&

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

&&

$$

DISCUSSION.....JLA/Goodin
AVIATION.......Kieckbusch