343
FXUS63 KGRB 240351
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1051 PM CDT Sun Jun 23 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Patchy fog may result in locally hazardous travel conditions
  late tonight.

- Runoff from recent rains will cause many rivers and streams to
  rise into the middle of the week. The threat of minor flooding
  will continue.

- Strong to severe thunderstorms capable of producing damaging
  winds, large hail and heavy rainfall are possible Monday night.

&&

.DISCUSSION...
Issued at 241 PM CDT Sun Jun 23 2024

Short Term...Tonight and Monday

Skies turned partly cloudy this afternoon as temperatures warmed
into the 70s. Regional radars were detecting isolated showers and
storms across portion of Upper Michigan and across northeast
Minnesota as of 2 pm. The showers and storms across Minnesota were
moving to the southeast.

For the rest of the afternoon into early this evening, an upper
level disturbance/500mb trough will swing across the area. This
feature will be catalyst for isolated/scattered showers and
thunderstorms to drop southeast across the area. Bufkit soundings
indicated 400 to 600 J/KG of CAPE with 0-6 km shear values of
40 to 50 knots. Some of the stronger storms could produce wind
gusts to 45 mph and small hail. It is not entirely out of the
possibility that a storm could go severe with damaging winds and
hail up to one inch in diameter. The showers and thunderstorm
activity should exit our southeast counties by 03z Monday.

Overnight, areas of fog will develop due to the combination of
clear skies, light winds and abundant moisture. The fog may be
locally dense in spots, especially across north-central Wisconsin.
Trended toward the cooler guidance values across the north due to
the longer duration of clear skies and light winds. Any lingering
fog will burn off quickly early Monday morning. Under partly
cloudy skies, highs should reach the upper 70s to middle 80s.

Long Term...Monday Night Through Sunday

The main forecast concerns revolve around the threat of severe
thunderstorms Monday night, and potential for heavy rainfall late
in the week.

A warm front will bring a threat of strong to severe storms into
the area Monday night. The storms should develop on the nose of a
40-45 kt LLJ, and just north of the warm front. Most models are
bring a linear/bowing MCS into our western counties late Monday
evening, then race it southeast during the overnight hours.
Even though this will be a nighttime event, models are showing
substantial instability developing over the area. Deep layer shear
will also be quite strong (35-50 kts), so severe weather looks
like a decent bet. Given the expected linear nature of the MCS,
damaging winds should be the main threat, though hail may occur
early in the event, and up to an inch of rain is also possible.
The track of the MCS is unknown, and likely dependent on the
location of the warm front, but current model consensus shows the
main threat area south of Hwy 29. Models are not showing much
redevelopment as the cold front moves through on Tuesday, but will
keep some low-end pops given lingering instability.

High pressure will bring dry conditions to the region from
Tuesday night through Thursday.

A frontal system is forecast to move through the region Friday and
Friday night. This system should have have a nice surge of Gulf
of Mexico moisture, with PWATs nearing 2 inches. Heavy rainfall
will likely be a concern, but a lack of significant instability
should limit the severe weather threat.

Aside from a very warm and humid day on Tuesday, most of the
extended period should average close to normal for temperatures.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1050 PM CDT Sun Jun 23 2024

Dry conditions are expected overnight. Continue to monitor fog
trends as some models want to bring in some lower
ceilings/visibilities, but SREF/HREF continue to show low
probabilities (under 30%) of under 3SM, so will just keep some
MVFR/IFR conditions in TEMPO groups. Ground fog may produce locally
lower visibilities as winds go variable overnight.

VFR conditions are expected on Monday with some fair weather
cumulus clouds expected, with some mid-high clouds spreading in
later in the day. A complex/line of showers and storms is
forecast to race across the region Monday evening/night, likely
after 03-06z Tuesday, but still some uncertainty as to where it
will track and how intense/widespread it will be. Have include a
TEMPO group at the end of the TAF period for AUW/CWA/RHI. Some
wind shear will also be possible Monday evening as winds aloft
increase to 35+ kts.

&&

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

&&

$$

DISCUSSION.....Eckberg/Kieckbusch
AVIATION.......Bersch