Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 201144

Area Forecast Discussion
National Weather Service Green Bay WI
644 AM CDT Thu Sep 20 2018

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 405 AM CDT Thu Sep 20 2018

A warm front over northern Illinois will work it`s way north
today, but will have a bit of a hard time with the cool outflow
from the convection along it. An increasingly strong low level jet
will produce showers and thunderstorms to the north of the front
as it moves north. The warm front could become the focus of
scattered strong or severe storms during the late afternoon and
early evening, as there will be strong shear, large CAPE, and low
LCL heights. Just not sure if there will be clearing to the south
of the front with resulting temperature differential helping to
produce storms. If storms do materialize, there is potential for
rotating ones with damaging winds, large hail and perhaps isolated
tornadoes. Highs today should be late in the afternoon, or even
in the early evening due to the cool stable air north of the

A surface trough will move through during the evening hours along
with gusty southwest winds. Winds in the boundary layer could be
strong enough to produce scattered wind damage with even weak
convection this evening. A cold front will arrive towards morning,
and be followed by cooler and drier air for Friday.

Rainfall of 1 to 2 inches are possible from early today through
tonight, with local higher amounts. Most of the region has had
little rainfall during the last two weeks, and could accept the
rain with no big trouble. Areas in Brown county that flooded with
localized heavy rains a couple of days ago, and the Lake Winnebago
basin could experience some problems if 2 inches of rain fall in
a short period of time.

.LONG TERM...Friday Night Through Wednesday
Issued at 405 AM CDT Thu Sep 20 2018

Frost potential Friday night into Saturday morning across
northern and parts of central Wisconsin and chances for showers
and storms early next week are the main concerns for this part of
the forecast.

Expect decreasing clouds and diminishing winds with the arrival
of surface high pressure that is forecast to move in behind the
departing cold front. This will allow temperatures to fall into
the 30s across much of the area late Friday night into early
Saturday morning, allowing areas of frost to develop in northern
and parts of central Wisconsin. Does not look like it will be
widespread, but will keep an eye on things to determine whether an
advisory will be necessary.

Return flow on the back side of the high should allow temperatures
to warm up enough to keep frost from becoming an issue through the
middle part of next week. The warmest days should be Monday and
Tuesday as south winds increase ahead of an approaching cold
front. The front will bring a chance for showers and thunderstorms
Monday night into Tuesday. The rest of the long term forecast
looks mostly dry.

.AVIATION...for 12Z TAF Issuance
Issued at 644 AM CDT Thu Sep 20 2018

Not the best day for flying today as a warm front will
be moving north across the area today, with IFR ceilings and showers
and thunderstorms. A strong low level jet could result in low level
wind shear and mechanical turbulence late this afternoon into tonight.
Winds at 2000 feet of 50 to 60 knots are possible with surface winds
around 20 knots.

The showers and thunderstorms will diminish or end late tonight.
MVFR ceilings and gusty surface winds are expected Friday, with a
chance of showers in the far north.



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