Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191133

Area Forecast Discussion
National Weather Service Green Bay WI
633 AM CDT Tue Oct 19 2021

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 333 AM CDT Tue Oct 19 2021

A ridge of high pressure will track east of the area today,
allowing southerly winds to provide warm air advection across the
region. Some mid and high clouds are expected at times; otherwise,
mostly sunny skies are expected. Well above normal temperatures
will continue as highs range from the upper 60s across the north,
with lower 70s across central and east-central Wisconsin.

A low pressure system will develop across the Plains tonight and
approach the upper Mississippi Valley. Although some models to
bring some light precipitation in across the region late tonight,
model soundings show quite a bit of dry air in the lower levels.
Therefore will keep the weather dry through tonight. Lows tonight
are expected to generally be in the 40s.

The aforementioned low pressure system will track over the upper
Mississippi Valley region on Thursday with the warm front from the
low extending east over central Wisconsin. Isentropic lift ahead
of the warm front will likely lead to showers and a few
thunderstorms across the region during the day on Wednesday, with
the best chance for precipitation during the afternoon hours when
isentropic lift is greatest. Although thunderstorms are possible
on Wednesday, the region is expected to be north of the warm
front; keeping the best instability to the south with only
elevated storms across northeast Wisconsin. Highs on Thursday are
expected to range from the middle 50s across the north, with lower
to middle 60s across central and east-central Wisconsin.

.LONG TERM...Wednesday Night Through Monday
Issued at 333 AM CDT Tue Oct 19 2021

The continuation of a low pressure system tracking across the region
Wednesday night into Thursday is the main focus from this forecast
period. Cooler air is expected to spread across the region following
this system, which will keep temperatures slightly below or
near normal.

Wednesday night through Thursday...Over the course of Wednesday
night into Thursday morning, a surface low pressure system will
track across the southern half of WI. Scattered showers are expected
to continue across the forecast area during this time, with a few
thunderstorms mainly south of Highway 29 Wednesday evening. The bulk
of the precipitation looks to stay focused ahead of the system`s
warm front, which puts almost the entire forecast area right in the
line of fire for the axis of heaviest precipitation. The showers
will taper off from northwest to southeast Thursday morning and end
during the afternoon. Additional rainfall amounts of 0.25 to 0.50
inches, mainly south of Highway 8, are forecast from Wednesday
evening to Thursday afternoon. The passing surface low will also
cause winds to shift to the north and increase across the forecast
area late Wednesday night through Thursday. These gusty winds will
create hazardous conditions for small craft on both the Bay and on
Lake Michigan. Much cooler air will fill in behind the surface low
for Thursday bringing high temperatures slightly below normal with
readings ranging from the middle 40s to low 50s.

Rest of the extended...For Friday and Saturday, model guidance is in
decent agreement with the forecast area remaining under an upper-
level northwest flow due to a closed low dancing over the
Ontario/Quebec border. Previous runs had this closed low dancing
further west, which brought a better opportunity for lake-effect
showers from the Great Lakes, but with the latest guidance`s
eastward trend, the lake-effect shower chances have decreased. This
is partly due to an upper-level ridge racing across the Northern
Plains on Saturday. Since the ridge`s evolution is not completely
clear yet, it is too early to determine the finer details of the
weekend`s forecast. However, it is still clear there will be a
period of cooler temperatures for Friday and Saturday with highs
ranging from the middle 40s to low 50s, and low temperatures ranging
from the middle 20s to middle 30s.

.AVIATION...for 12Z TAF Issuance
Issued at 633 AM CDT Tue Oct 19 2021

Mostly clear skies, excellent visibility and light surface winds
are expected through tonight. Marginal wind shear may develop
tonight across the central and north-central sites (AUW, CWA,
RHI). Otherwise, an approaching low pressure system will bring
showers and IFR conditions by Wednesday afternoon over most of the



SHORT TERM.....Kurimski
LONG TERM......Hykin
AVIATION.......Kurimski is the U.S. government's official web portal to all federal, state and local government web resources and services.