311
FXUS63 KGRB 050004
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
704 PM CDT Thu Jul 4 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Areas of showers and embedded storms are expected this evening
  into Friday. Some storms across central Wisconsin may become
  strong to severe through early this evening, with the main
  threats being flooding, gusty winds, and small hail.

- Elevated potential for flooding this evening into Friday. River
  and stream levels will likely be on the rise, with some urban
  flooding also possible depending on where swaths of heaviest
  rain occur.

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

&&

.DISCUSSION...
Issued at 409 PM CDT Thu Jul 4 2024

Severe & Heavy Rain Threat / Precip Chances:

Area of light rain and sprinkles, along with an embedded storm or
two, will continue to track northeast across the area through the
mid and late afternoon. Some additional activity will continue to
peculate to our south and drift towards/into the southern
counties through sunset. Instability has built up to 800-1000 J/kg
despite the cloud cover, with an area of higher instability just
to our south. While widespread severe weather is not expected,
can`t rule out a strong to severe storm south of Hwy 29 through
early evening as any storm taps into this instability to our south.
A more organized area of convection will continue to develop
across southeast MN and northeast IA and work east toward our
area, as the main shortwave and surface/upper low track eastward.
This looks to push east across the southern 2-3 row of counties
later this evening. Instability will be slowly waning through the
evening, so the severe threat will lower as we head toward
midnight. Current timing has this area just to the west of the
Fox Valley around firework time, but locations to the west will
likely be impacted by these showers/storms. The shortwave/low
will slowly work across the area on Friday, keeping scattered
showers and isolated storms going for much of the day. With a
north/northeast wind kicking in, it is not looking like the best
early July day for outdoor activities. The shower/storm activity
will diminish toward sunset and end across far eastern WI by
midnight.

Complex flood threat this afternoon into Friday as areas of
convection will bring locally higher totals (0.5-1.0" per hour
rates) across parts of central and east-central WI, and locations
in the comma head will see a more steadier rain over far northern
WI. Favorable antecedent soil moisture conditions exist across
parts of central and east central WI due to recent heavy rain
events. But we have had 1.5-3+ days in between heavy rain events
which has allowed many rivers/streams to decrease. But the ground
is still pretty saturated, with flash flood guidance (FFG) still
between an inch or two in the Fox Valley, slightly lower in parts
of Brown Co. This looks to be the most vulnerable area. Parts of
central WI will need to be monitored as well with FFG between
1.5-2.5". But with the rounds/bursts of heavier rainfall expected
to be separated by a few hours and models trends for a more
progressive first round (or possibly missing some of the area),
will hold off on a flood watch but continue to highlight in the
HWO. If the heavier rain (1-2 inches) occurs across the areas with
the lower FFG this evening, some flood advisories may be needed.
Plus, the locations where the heaviest rain falls tonight will be
more susceptible to flooding on Friday.

Saturday is still looking mainly dry, aside for a few light
showers or sprinkles in the afternoon/evening, as high pressure
makes a brief stop over the western Great Lakes. A stray storm
will also be possible some instability builds through the day.
Have bumped up cloud cover as plenty of daytime cumulus are
expected as well. The pattern turns unsettled once again Sunday
into at least Tuesday as another large trough slowly rotates
across the western Great Lakes. Some bouts of heavy rain will once
again be possible with PWATs climbing back to near 1.75", possibly
creating additional flooding concerns.

Fog / Temps:

Some fog will be possible tonight as winds will stay on the light
side and recent rain. But with plenty of rain/clouds around, it
looks to not be dense. There will be additional fog chances during
the overnight and early morning hours this weekend, especially
after the heavier rain events and if/when skies clear.

A brief cool down arrives on Friday with highs stuck in the 60s
across much of northern WI and low to possibly mid 70s further
south. Temps rebound quickly to close to or slightly above normal
for the weekend and into next week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 652 PM CDT Thu Jul 4 2024

An upper level low pressure system will move slowly
from southern Minnesota to northern Wisconsin and produce periods
of showers and thunderstorms tonight and Friday.

VFR conditions will lower as the rain arrives from west to east
this evening. IFR conditions are expected from around 09z through
15z Friday west of a ESC to GRB to OSH line, with MVFR conditions
to the east. Ceilings and visibilities will improve a bit Friday
afternoon across the area.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......RDM