Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 190014
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
714 PM CDT Mon Sep 18 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 243 PM CDT Mon Sep 18 2017

A northeast to southwest area of showers moved into north central
Wisconsin this afternoon. Mid level short wave energy and
isentropic lift due to warm advection appear to be the main
reasons for the showers. Models were showing measurable rainfall
in much of the forecast area this afternoon and evening, with
little or nothing later tonight or Tuesday morning.

Strong warm advection should bring much above normal temperatures
to the area on Tuesday. Highs away from Lake Michigan will he
mainly in the lower to middle 70s.

.LONG TERM...Tuesday Night Through Monday
Issued at 243 PM CDT Mon Sep 18 2017

A warm front lifting north through the western Great Lakes region
will bring showers and thunderstorms to the area Tuesday night
into Wednesday morning. Instability will be fairly marginal
during this initial band of precipitation so severe weather is not
expected.

Later Wednesday afternoon and evening a cold front will sweep
through the western Great Lakes region. This front will have 2 to
3 J/g of MUCAPE available to it along with 30 to 40 knots of bulk
shear and 1.5 to 1.75 inches of PWAT. Despite the instability and
shear, dynamics are expected to be fairly weak with the main
shortwave tracking northeast away from the region as the cold
front passes through. However the timing of the cold front, during
the afternoon and evening hours, will be favorable for showers
and thunderstorm development as it moves through the area. Given
the instability, shear, and moisture any thunderstorms that form
ahead of the cold front will have a marginal risk to be severe,
with gusty winds, large hail, and heavy rain being the main
threats.

The cold front will fizzle out as it tracks through the region
Wednesday night and linger across the region through the end of
the week. This will keep the chance for showers and thunderstorms
across the area as high temperatures soar into the middle to upper
80s across the region on Friday. Ridging will keep these warm
temperatures in place across the western Great Lakes during the
weekend, with fairly dry weather expected across most of the cwa.
An area of low pressure will stall out over the upper Mississippi
Valley during this period, with some showers and thunderstorms
possibly spilling over into extreme northwestern sections of
north-central Wisconsin.

This low will eventually slowly track east next Monday as the
upper level ridging moves east, bringing showers and thunderstorms
back to the region as high temperatures fall back into the 70s
under mostly cloudy skies.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 713 PM CDT Mon Sep 18 2017

Band of mainly light showers moving across central Wisconsin early
this evening. Radar trends last few hours has indicated intensity
of shower activity has been diminishing steadily. Short-term
model guidance suggests only isolated light showers or sprinkles
will remain by the time the activity gets into eastern Wisconsin
around midnight as weak upper-level impulse moves away from the
area. Although ceilings will generally remain in the VFR category,
some areas of MVFR cigs are possible especially over central
Wisconsin where light precipitation has been a bit more
widespread. However, confidence was not high enough to go below
VFR after midnight for this issuance given current rapid decay of
light precipitation. Generally VFR conditions on Tuesday as weak
upper ridging commences downstream of robust shortwave trough
approaching the intermountain west.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Kurimski
AVIATION.......ESB



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