632
FXUS63 KGRB 012346
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
646 PM CDT Sat Jun 1 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Scattered showers/isolated thunderstorms into early this
  evening. No severe storms anticipated.

- Areas/patchy fog expected to develop late this evening through
  daybreak Sunday. Some of this fog may become locally dense,
  mainly across central and north-central Wisconsin.

- Rain and storms are possible Monday afternoon. While storms are
  not expected to be severe, an isolated strong gust up to 35 to
  40 mph with any storms is still possible.

- A better chance for strong storms arrives later in the day Tuesday.
  These storms may also be accompanied by heavy rainfall.

&&

.DISCUSSION...
Issued at 215 PM CDT Sat Jun 1 2024

Short Term...Tonight and Sunday

Main forecast concerns to be on precipitation trends through this
evening, potential for locally dense fog later tonight and how
warm to take temperatures on Sunday.

The 19Z MSAS surface analysis showed a weak cold front that
extended from northeast MN south through far western WI into
east-central IA. High pressure was situated over the Dakotas.
Latest radar imagery indicated a band of light showers over
eastern WI and scattered showers over central WI. Temperatures
were being held in check by thick cloud cover and precipitation
with readings in the 60s.

The chance of showers/few thunderstorms will carry over into the
evening over parts of the forecast area as the weakening cold
front slides across the region and a mid-level shortwave trough
lifts northeast into the Great Lakes. While the precipitation
diminishes/ends later this evening, lingering low-level moisture
coupled with light/variable winds are expected to generate fog
overnight. This fog may become locally dense, especially over
central WI where heavier rains fell earlier in the week. This fog
may extend into the Bay and Lake MI as well, especially the lake
where the higher dew points are moving over cooler lake waters.
Min temperatures to be in the upper 40s to around 50 degrees
north, lower to middle 50s south.

The weak area of high pressure over the Dakotas will move into the
Great Lakes on Sunday, thus once any fog dissipates, look for
mostly sunny skies to prevail. Max temperatures to range from
around 70 degrees near Lake MI, middle 70s to around 80 degrees
inland.

Long Term...Sunday Night Through Saturday

An active weather pattern will continue for the first part of the
work week, with chances for light rain at times late into the week
into next weekend.

A low pressure system developing across the Plains will bring the
first chance for rain late Sunday night through Monday night as it
tracks through the western Great Lakes region. Despite decent
dynamics, instability with this system is not all that impressive,
with MUCAPEs of 300 to 800 J/kg. The muted instability is due to
the cloud cover that is expected to move into the region late
Sunday night and continue through Monday night, which will prevent
instability from getting out of hand. Therefore, severe weather is
not expected from this first round of showers and thunderstorms.

Behind this departing system Monday night, another system will be
hot on its heels as another system developing over the Plains
tracks through the western Great Lakes Tuesday and Tuesday night.
Instability will be a lot higher with this second system, as
MUCAPEs rise to 1000 to 2000 J/kg; however, bulk shear will only
be around 20 knots. There could be some strong storms Tuesday
afternoon and evening given the high instability, but severe
weather is not expected given the relatively meager shear;
however, this period in the forecast will bear watching for
changes in these parameters.

The low associated with this system will cut off and spin over
southern Manitoba during the middle part of the week then move
slowly east through the northern Great Lakes region through early
next weekend. As this low meanders through the Great Lakes,
several additional rounds of light rain are expected at times to
end the work week and into next weekend. This low will also bring
an end to the above normal temperatures experienced earlier in
the week, as temperatures fall below or around normal for the late
part of the week into next weekend.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 645 PM CDT Sat Jun 1 2024

Any light showers are expected to come to an end early this
evening. However, lingering low-level moisture, light winds, and
partial clearing will create favorable conditions for fog
development this evening and overnight. Visibilities are expected
to drop to at least MVFR at most TAF sites, with some IFR and
potentially LIFR visbys possible at CWA and AUW where clearing
skies are expected. IFR visbys may also be possible at MTW given
assistance from low-level lake moisture. A brief period of LIFR
visbys may occur, although confidence was too low to include in
the TAF.

After fog burns away Sunday morning, expect VFR conditions at all
sites as weak high pressure moves across the region. Some
scattered daytime cumulus may develop during peak heating early
Sunday afternoon and linger through the evening, although cigs are
expected to remain VFR.

&&

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

&&

$$

DISCUSSION.....Kurimski/Kallas
AVIATION.......Goodin