925
FXUS63 KGRB 022353
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
653 PM CDT Tue Jul 2 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Another round of showers and embedded storms will push across
  mainly central and eastern WI late this afternoon and evening.
  Highest rain totals are expected across east-central WI, where
  some locations could see over an inch. The rain could lead to
  minor river and stream flooding, along with urban flooding and
  ponding on roads.

- Conditions will be hazardous to mariners and beachgoers on the
  bay and Lake Michigan through early Wednesday due to gusty
  winds and high waves.

- There is a 50-percent chance to get measurable rain in central
  Wisconsin sometimes Thursday afternoon and evening, with around
  a 25-percent chance in far northeast WI during the same time.
  The better chance for rain and a few thunderstorms arrives
  Friday.

&&

.DISCUSSION...
Issued at 345 PM CDT Tue Jul 2 2024

Short Term...Tonight and Wednesday

This Afternoon into Tonight:

The lull in the heavier/widespread shower activity will continue
early this afternoon, but come to a quick end as another large
area of showers and embedded storms will push northeast across
mainly central and eastern WI. The showers/storms will be
associated with a shortwave trough swinging across the western
Great Lakes, along with an approaching weak front, weak LLJ and
the RRQ of an upper jet. PWATs around 2" will favor some heavier
rain through the evening, with the heaviest swath of rain expected
to be across east-central WI, where some totals could top one
inch. Overall flood threat looks low as the rivers have had a
chance to come down and this area of rain will be moving through
pretty quickly, but some minor low-land flooding and ponding on
roads will be possible where the heaviest rain falls/training
storms occur. The activity will end overnight with clouds slowly
towards/after sunrise on Wednesday. The gusty south winds will
slowly weaken through the late afternoon and evening hours. It
will be a relatively warm and humid night, with lows mainly in the
60s expected.

Wednesday:

Dry conditions are expected for most of the day. However, some of
the latest CAMs (especially the HRRR) are showing some showers
developing in the heat of the day as a weak boundary drops across
the area. If we can get some showers to pop, could be enough
instability (up to 1000 J/kg) to get a rumble of thunder as well.
Have added some low chance PoPs to account for this chance. West
winds look to gust to 25-35 mph. Highs will be in the 80s for
most spots, with humidity levels remaining high across central and
east-central WI as dewpoints remain in the 60s.

Long Term...Wednesday Night Through Tuesday

Focus is on the July 4th forecast and the potential for any rain
and thunderstorms, along with temperatures.

Wednesday night through Thursday night...Upper level pattern
shows broad troughing across the Northern Plains and into the
western Great Lakes, with multiple embedded shortwaves rotating
into Wisconsin which will lead to opportunities for precipitation.
The best chance will be Friday when the associated surface low
also moves through Wisconsin.

Good consensus that conditions will be dry Wednesday night through
Thursday morning, but there is more variable when the first wave
will impact central and northwest Wisconsin later Thursday, which
impacts when any rain would begin. Some models show scattered rain
activity as early as 11AM/Thurs, while other hold off until after
midnight. NBM probability of precipitation greater than 0.01
inches before 1AM/Fri is right around 50-percent across all of
central Wisconsin, and gradually decreases towards the east, with
the Fox Valley anywhere from 25 to 45 percent, and less than
25-percent in far northeast WI and along Lake Michigan.
Increasing precipitation to 0.10 inches the percentages decrease
significantly, with around a 25-percent chance of getting this
much rain by 1AM/Fri in central WI. All this to say, there could
be some rain Thursday afternoon and evening, especially in central
WI, but amounts will be rather light and scattered, with more
widespread rain chances holding off until Friday associated with
the low. Thunderstorms are also possible, but with instability in
the 300 to 600 J/kg range and lapse rates around 5.5 C/km do not
currently expect severe thunderstorms.

High temps on Thursday will be AOA normal from the upper 70s to
low 80s.

Friday...Rain becomes more widespread. Again, some thunderstorms
are possible within the rain, but rain will be the main focus. The
rain and clouds will lead to a cooler day, with highs in the mid
60s to low 70s.

Saturday through early next week...Surface low moves east leading
to mainly dry conditions and temps rebounding into the mid to
upper 70s on Saturday. With some lingering moisture and small bits
of mid-level energy would not be surprised to see a few brief
showers. The overall upper troughing pattern continues into early
next week with shortwaves and fronts bringing on and off chances
for showers and thunderstorms.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 642 PM CDT Tue Jul 2 2024

A large swath of moderate to heavy rain showers and a few
embedded storms will impact the forecast area this evening,
then pull out of eastern WI overnight. The best chance of storms
should occur at the eastern TAF sites this evening, as a low-
level jet strengthens there this evening.

Widespread MVFR/IFR conditions will deteriorate to IFR/LIFR
later this evening and overnight. Increasing west winds should
cause ceilings to rise slightly late tonight, 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 acknowledge these in
the TAFs at this time.

LLWS will impact the eastern TAF sites (GRB/ATW/MTW) this evening
and into the early overnight period, then weaken late tonight.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through Wednesday morning for WIZ022-040-
050.
&&

$$

DISCUSSION.....Bersch/KLJ
AVIATION.......Kieckbusch