090
FXUS63 KGRB 180915
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
415 AM CDT Tue Jun 18 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Hot and humid weather is expected today, with heat indices in
  the low to mid 90s in most places. A few places in the Fox
  Valley and west of the bay could have heat indices in the upper
  90s. It will be considerably cooler near the Lake Michigan
  shore.

- Gusty south winds could create large waves and strong currents
  at Lake Michigan beaches this afternoon and tonight. A Beach
  Hazard Statement has been issued.

- The gusty south winds will also create conditions hazardous to
  small craft on the lake and bay today and tonight.

- Thunderstorms are likely in central and northcentral Wisconsin
  tonight, and in eastern Wisconsin Wednesday. Some storms could
  produce strong winds and torrential rains.

&&

.DISCUSSION...
Issued at 413 AM CDT Tue Jun 18 2024

Short Term...Today...Tonight...and Wednesday

The surface warm front was approaching the Michigan border at
09z. Wisconsin will be in the warm sector of the surface low
lifting north across the Plains states today. The models really do
not show any significant upper air or surface feature to trigger
thunderstorms today, though there is plenty of warmth and moisture
in the atmosphere. There could be isolated storms this afternoon,
perhaps along a lake breeze, but left them out due to low
probability.

Hot and humid weather is expected today, except near the lakeshore.
Heat indices will be mostly in the low to mid 90s away from the
lake, with a few places in the Fox Valley and west of the bay
reaching the upper 90s. It will be much cooler near the Lake Michigan
shore, with highs in the lower 70s but with a gusty wind.

Thunderstorms will move into central and northcentral Wisconsin
tonight as the cold front moves into northwest Wisconsin. A few
storms with strong winds and torrential rain are possible. High
dewpoints and clouds will make for a very mild night, with lows in
the 70s in most places. Thunderstorms will arrive in eastern
Wisconsin Wednesday as the cold front moves slow across the
state. Highs will range from the middle 70s in northcentral
Wisconsin to the low 80s in the Fox Valley.

Long Term...Wednesday Night Through Monday

 An unsettled pattern is forecast to persist through much of the
extended period with low to middle end PoPs (30-70%) progged for
each day through Sunday. With the chance for successive rounds of
showers and storms and anomalously high available moisture, minor
flooding as well as rising levels on area rivers and streams
looks to be the main impact through the extended period.

Wednesday night through Sunday...A few showers and thunderstorms
may linger across east-central WI into Wednesday night as a cold
front departs the region. Expect mostly dry conditions across the
rest of the region overnight into Thursday morning as cold air
advection behind the front brings an area of widespread
subsidence. This dry spell looks to be rather short lived as
models show return flow bringing a surge of warm moist advection
into the upper-Midwest. An upper-level right rear jet quad is
progged to provided additional synoptic scale ascent during this
period. The severe weather potential during this period looks
rather low given weak instability and the lack of a more robust
forcing mechanism.

A developing low-level jet overnight Thursday into Friday morning
may be able to sustain some isolated to scattered showers, but
with nocturnal stabilization this may be another period during
which the region could see a lull in the precipitation. The
chances for widespread rain with embedded thunderstorms then
increase Friday with another surge of warm moist air out ahead of
a developing low pressure system. With PWATs forecast to approach
1.75-2 inches (near 99th percentile of climatology) periods of
heavy rain fall will be possible, particularly along warm front
which is forecast to set up across northern WI. The severe
weather potential does increase Friday afternoon and evening
compared to Thursday, especially across central WI where SBCAPE
are forecast to reach 1000-1500 J/kg and effect shear values
range from 25-30 kts. However, with widespread cloud cover
expected and a lack of a clear cut forcing mechanism there are
pitfalls that may hinder storm development during this period.

As the axis of anomalously high available moisture and low
pressure system continue to propagate across the region through
Saturday periods of heavy rain are expected to continue. The best
chance for severe weather during the extended period may come
Saturday afternoon and evening as the attendant cold front sweeps
across the region. There is a high level of uncertainly with the
severe potential during this period, but currently long range
guidance is showing upwards of 2000 J/kg MUCAPE and effect shear
of 20-30 kts which could support some stronger to severe storms.
Behind the cold front perception should become more scattered
with areas of showers lingering into Sunday as the region remains
in the cyclonic flow, but the threat to any severe weather Sunday
looks minimal at this time.

In terms of the flooding potential, long range ensembles are
forecasting about 2-2.5 inches of QPF from Wednesday night
through Sunday across the region. Locally higher amounts may be
possible if heavier rainfall hits the same area multiple times.
WPC has introduced a slight risk (15%) for excessive rainfall
across northern WI and a marginal risk (5%) across central and
east-central WI both Friday and Saturday.

Rest of the extended...Long range ensembles are in decent
agreement with a broad low amplitude ridging moving over the
region Monday. Expect this ridge to bring a more prolonged period
of dry and seasonal weather to start next week.

Temperatures...While temperatures may trend a few degrees above
normal each day during the extended there is only a minor risk of
heat related impacts.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1152 PM CDT Mon Jun 17 2024

VFR conditions prevailed across the area late this evening, as
the evening showers/storms exited/weakened. Mainly VFR conditions
are expected tonight, with some lower MVFR ceilings impacting
northern WI (RHI) during the early overnight hours. A brief shower
or storm will remain possible overnight as well, locally lowering
flying conditions. A broken line of showers and storms will
approach from the west after 00z Wednesday, likely reaching the
Fox Valley and lake shore after 06z Wednesday. Instability will
be waning, so thunder chances will also be decreasing through the
evening hours. Will not include any thunder mention this far out.

Surface winds will remain under ~10 kts overnight, with LLWS
expected as winds at 2000 ft increase to around 30kts. It will be
a hot and humid Tuesday, with VFR conditions expected most of the
day. Breezy south winds are expected, gusting to 30 kts. A few
higher gusts are possible during peak mixing. Another period of
low-end LLWS is expected Tuesday evening if/where surface winds
stop gusting.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 10 AM CDT this morning through
Wednesday morning for WIZ022-040-050.
&&

$$

DISCUSSION.....RDM/GK
AVIATION.......Bersch