382 
FXUS63 KGRB 212036
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
336 PM CDT Sat Aug 21 2021

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 335 PM CDT Sat Aug 21 2021

The main focus from this forecast period has been precipitation 
trends with the expected passing of a weak cold front. Behind this 
cold front, dry conditions and near normal temperatures are forecast 
for tonight and Sunday.

This afternoon's satellite imagery and surface observations 
indicated the cold front was positioned along a line from Iron 
Mountain to Wautoma. Meanwhile, across east-central WI, the KGRB 
radar showed an uptick of a few, very broken, bands of convection 
this afternoon. CAMs indicate this isolated to scattered convection 
will exit the region to the east by 00z this evening. While severe 
weather is not expected, marginal instability and limited deep-layer 
shear could support a storm with gusty winds. High pressure and dry 
air following the cold front will provide clear skies overnight into 
Sunday.

In addition, cooler air will spread across the area, allowing 
near normal low temperatures overnight ranging from the upper 40s 
to upper 50s inland, and the lower 60s along the lakeshore. The 
near normal temperatures will continue for Sunday afternoon with 
highs in the middle to upper 70s.

.LONG TERM...Sunday Night Through Saturday
Issued at 335 PM CDT Sat Aug 21 2021

A weak mid level PV anomaly and weak isentropic lift could bring
some showers and a few thunderstorms to north-central and central
Wisconsin late Sunday night, with eastern Wisconsin remaining dry
as the area of showers dives south Monday morning. Behind this
activity, temperatures and dew points will increase across the
western Great Lakes, pushing heat index values close to 90 during
the afternoon. Despite MLCAPE values rising to around 1500 J/kg 
during the afternoon hours on Monday, there will be a substantial 
capping inversion in place with no trigger mechanism to overcome 
the cap. Therefore, dry weather is expected on Monday per the CAMs
models.

A cold front will track through the region Tuesday afternoon into
Tuesday night as the NWP models develop a thunderstorm complex
upstream and track it through Wisconsin. The complex will have
1000 to 2000 J/kg of MUCAPEs to work with along with 30 knots of
bulk shear; therefore, there is the potential for strong to severe
storms if the complex comes through with enough instability. High
pressure will build in behind the departing cold front, which is
expected to bring dry weather by Wednesday afternoon.

The forecast becomes a bit more muddled as we head towards the end
of the work week and into the early part of next weekend as the
NWP models do not have great agreement with a series of low
pressure systems that track through the region. The overall
consensus seems to be towards a more active period in the forecast
for late in the week and into the early part of next weekend as
these systems track through. Although the threat for severe
weather at this point is too far out to determine, any
thunderstorms that develop during peak heating have the potential
to be strong to severe if the shear is also sufficient.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 100 PM CDT Sat Aug 21 2021

Scattered MVFR and low-end VFR cigs prevailed across the TAF sites
this afternoon ahead of an approaching cold front. Little to no
precipitation has fallen from these clouds; however, a few showers
and storms have popped up over Lake Michigan early this afternoon.
The main uncertainty is the extent of additional redevelopment
this afternoon and evening. Models continue to paint a few 
showers and storms developing and moving across the ATW, GRB, and
MTW TAF sites from west to east beginning around 20z. The showers
and storms would then exit the region by 00z this evening. Have
accounted for the storm potential with TEMPO groups at these TAF
sites. Clouds will clear into this evening as the cold front exits
the region to the east.

Meanwhile, the breezy west to southwest winds this afternoon will
turn northwest and decrease this evening behind the cold front, 
then turn north overnight. Winds will then increase slightly and 
turn northeast Sunday morning. The breeziest winds will impact the
east-central WI TAF sites Sunday morning.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 10 PM CDT this evening for WIZ022.
&&

$$

SHORT TERM.....Hykin
LONG TERM......Kurimski
AVIATION.......Hykin