Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 092345

Area Forecast Discussion
National Weather Service Green Bay WI
645 PM CDT Wed Aug 9 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 202 PM CDT Wed Aug 9 2017

Primary challenge during this period is timing the passage of a
short wave trough and frontal system with associated convection
across the area through Thursday.

SB and MU capes indicate the most unstable air positioned over
north central Wisconsin into Upper Michigan early this afternoon.
Isolated convection continues to develop in this area and drift
northeastward. Anticipate this will be the trend for much of the
remainder of the afternoon and into early evening with isolated
convection developing in the warm air advection over central and
north central Wisconsin. Both morning raobs from GRB and MSP
indicate plenty of dry air in the mid levels, which is holding the
convection in check this afternoon. Better region of isent lift
with a weak looking MCV type system was working into far west
central Wisconsin early this afternoon. Short range progs indicate
this feature to lift over the northwest third of the state
through tonight including parts of north central Wisconsin and
then into upper Michigan overnight. The rest of the area will
have lower end pops starting late but will eventually get more
into warm air advection sector.

Then the next round of convection associated with the main upper
short wave with cold front to track over the area Thursday. This
upper system was still centered over northern North Dakota early
Wednesday afternoon. Lightning data this Wednesday afternoon
indicated storms were mostly concentrated near the upper system
over North Dakota, and in the stronger warm air advection over
northwest Wisconsin.  Although off to a slow start, progs drive
this upper system over the area Friday with the cold front
sliding over at least central and north central Wisconsin in the
afternoon and approaching eastern sections late afternoon. Best
instability was noted in the afternoon hours before tapering off
late in the day.

.LONG TERM...Thursday Night Through Wednesday
Issued at 202 PM CDT Wed Aug 9 2017

Showers and isolated storms will be on the decrease Thursday night
from west to east as an upper trough axis and surface low
pressure system depart east of the region.

Isolated showers and clouds may linger Friday in the cyclonic
flow, otherwise an overall drier and quiet stretch of weather is
expected for the weekend and into much of next week. Surface high
pressure settles into the Western Great Lakes Saturday into
Sunday. There are small chances for showers later Sunday as a
weak upper short wave trough drops into the area. For the start of
next week, another surface high pressure region drops into the
area as an upper ridge builds over the Plains. Progs divert a bit
with another short wave trough dropping over the area toward next
tuesday for another chance of showers.

Cooler temperatures expected Friday with anticipated clouds.
Temperatures at or slightly below normal for the rest of the

.AVIATION...for 00Z TAF Issuance
Issued at 633 PM CDT Wed Aug 9 2017

Showers will become more numerous from west to east tonight
into early Thursday. Instability will be weak, so only isolated
thunderstorms are anticipated. Ceilings are expected to lower to
MVFR and IFR over north central and parts of central Wisconsin,
especially after the showers taper off late tonight into early
Thursday. A strong upper level disturbance and associated cold
front will move through the area during the afternoon, and will
bring an increased chance of thunderstorms to all of the TAF
sites. Some storms may be strong, with small hail, gusty winds and
heavy rainfall.



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