Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 301137
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
637 AM CDT Fri Jul 30 2021

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 405 AM CDT Fri Jul 30 2021

Canadian high pressure will bring dry weather and partly cloudy
skies to the forecast area today. Smoke models suggest that there
will be minimal impact from smoke, so air quality and visibility
should be good. It will be significantly cooler and less humid,
especially over central and east central WI. High temperatures
should be in the middle 70s, except upper 60s and lower 70s near
Lake Michigan.

After a quiet start tonight, a cold front will bring a small
chance of showers and perhaps a storm to far northern WI late
tonight. Lows will be in the middle 50s to lower 60s.

On Saturday, the cold front will drop south through the forecast
area. The front will combine with the passage of a short-wave
trough in the afternoon to produce showers and scattered
thunderstorms. With SBCAPE of 1000-1500 j/kg, deep layer shear of
25 to 35 kts and favorable wet bulb zero heights, conditions
should be supportive of isolated strong to severe thunderstorms.
The Day 2 Marginal Risk of severe thunderstorms from SPC looks
good. Smoke models show smoke returning to the region, though it
is difficult to gauge the visibility/air quality impacts on a day
when scattered to numerous showers are anticipated. High
temperatures will be in the 75 to 80 range.

.LONG TERM...Saturday Night Through Thursday
Issued at 405 AM CDT Fri Jul 30 2021

The latest ensemble means indicate that an amplified ridge-trough
pattern across North America this weekend will deamplify next week
as the mean western ridge folds towards the Great Lakes.  Under
northwest flow, the region will see occasional thunderstorm chances
until ridging arrives towards next Thursday.  Trying to pin point
these thunderstorm chances is the main forecast concern.

Saturday night through Sunday night...A cold front will be dropping
south across central and east-central WI on Saturday evening, which
may be a tad slower than model solutions portrayed 24 hours ago. As
a result, expanded precip chances to the northwest for Saturday
evening. A scattered strong to isolated severe storm chance will
continue due to lingering instability in the 1000-1500 j/kg range,
but storms in general should be weakening with loss of heating
before the front exits.  Behind the front, breezy north winds will
bring in a colder airmass for Sunday.  Highs in the low to mid 70s
is likely.  A shortwave will be digging across the region on
Saturday night.  But with high pressure at the surface, the airmass
appears too dry for precip chances.

Rest of the forecast...After a dry Monday, there are some
indications that another cold front will drop south across the
region on Tuesday.  Not confident that models depict this front
accurately due to the inherit uncertainty in this type of weather
pattern.  Precip chances will therefore remain low.  Then high
pressure returns for Wednesday and Thursday which looks seasonable.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 633 AM CDT Fri Jul 30 2021

Canadian high pressure will bring VFR conditions to most of the
area through the TAF period. Patchy MVFR/IFR fog in northern WI
will mix out early this morning. Scattered diurnal cumulus can be
expected in the late morning and afternoon. A cold front will
bring thickening cloud cover and a chance of showers to far
northern WI late tonight.

Smoke models suggest that there will be little impact from near-
surface smoke during this TAF period, but the smoke may return on
Saturday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......Kieckbusch


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