277
FXUS63 KGRB 211915
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
215 PM CDT Fri Jun 21 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Several rounds of thunderstorms with heavy rain are likely
  across central and east-central Wisconsin through Saturday
  evening. The heavy rain could result in flash flooding,
  especially in urban areas. A Flood Watch for flash flooding is
  in effect through early Saturday evening along and south of
  Highway 29.

- Strong to severe thunderstorms are possible across central and
  east-central Wisconsin Saturday afternoon and evening. Damaging
  winds, a few tornadoes and torrential rainfall will be the
  primary threats.

- Additional strong to severe thunderstorms are possible Monday
  night into Tuesday evening.

&&

.DISCUSSION...
Issued at 210 PM CDT Fri Jun 21 2024

Short Term...Tonight and Saturday

Several rounds of showers and thunderstorms are expected across
the region through Saturday as a warm front slowly lifts north
across the western Great Lakes region. Although the CAMs models
aren`t in great agreement regarding exact timing and placement of
this activity, there seems to be some consensus that another round
will track east through the area later this afternoon into early
this evening, then again Saturday morning, and yet again Saturday
afternoon. The initial rounds should not be surface based, which
will limit the severe weather potential. However, moderate to
heavy rain is possible from these rounds of rainfall into the
early part of the weekend.

Although the first rounds of convection are not expected to be
severe, the third round Saturday afternoon could be problematic
based on where the warm front ends up. There are some indications
the warm front could lift as far north as southern portions of
central and east- central Wisconsin, which would mean an increased
threat for severe weather as model soundings are quite
impressive. Specifically, SBCAPEs could be as high as 1-2 J/g
with 0-1 km SRH values of 300 to 600 and Supercell Composite
numbers of 3 to 6. There will be quite a bit of instability and
low level helicity near the warm front, which will mean an
increased threat for wind damage and tornadoes given the curved
hodographs. Large hail will not be as big of a threat given the
skinny CAPE profiles in the hail growth zone and wet-bulb zero
heights of 12-14k ft. That being said, if the warm front ends up
being further south due to the convection pushing the front
further south, the severe weather threat across our area would be
de minimis.

Long Term...Saturday Night Through Friday

The main forecast concerns revolve around thunderstorm and severe
weather threats Saturday evening and Monday night through Tuesday
evening.

Models show low pressure and an associated warm front moving
through EC WI Saturday evening, along with a potential severe
weather and heavy rainfall threat. There is some concern about the
degree of instability that will be present, as earlier convection
could hold the front just south of the area. If everything comes
together there could be a damaging wind/tornado/flooding threat in
east central WI during the early evening. Short-wave energy
moving through northern WI will also support continued showers and
isolated storms there.

Although Sunday still looks like the overall better weekend day, a
short-wave moving through during the afternoon and early evening
is expected to generate scattered showers and a few thunderstorms.

After a brief break in the precipitation Sunday night into
Monday, a warm front will bring a chance of storms back into the
area Monday night. Substantial instability will develop across the
forecast area later Monday night into Tuesday. Strong to severe
elevated storms are possible later Monday night, with surface
based storms possible ahead of a cold front Tuesday into Tuesday
evening.

Mainly low-impact weather expected for the latter half of the work
week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1158 AM CDT Fri Jun 21 2024

Periods of showers and thunderstorms are expected during the TAF
period as a warm front slowly lifts north from northern Illinois.
After this first round of thunderstorms moves through early this
afternoon, additional thunderstorm timing is problematic as CAMs
models each have a different solution. Most of the models seems to
be honing in on additional thunderstorms moving in later this
afternoon and again sometime Saturday morning. Conditions are
expected to fall to MVFR and eventually IFR as low level moisture
and showers increase across the region. Significant rain is
possible at times, with moderate to heavy showers.

&&

.HYDROLOGY...
Issued at 210 PM CDT Fri Jun 21 2024

Rainfall reports from this initial batch of thunderstorms that
moved through this morning and early this afternoon indicate that
anywhere from 0.70 to around 1 inch of rain fell from this
activity. Several more rounds of rainfall are expected later this
afternoon through Saturday, each round possibly producing 0.50 to
1 inch of rain, for a total of 1 to 3 inches with locally higher
amounts possible. The highest amounts appear to be across central
and east-central Wisconsin where the heaviest rains will likely
hit these areas several times. Therefore, will issue a Flood Watch
for central and east-central Wisconsin through Saturday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday evening for WIZ030-031-035>040-045-
048>050.
&&

$$

DISCUSSION.....Kurimski/Kieckbusch
AVIATION.......Kurimski
HYDROLOGY......Kurimski