Area Forecast Discussion
Issued by NWS Green Bay, WI

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422
FXUS63 KGRB 280324
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1024 PM CDT TUE SEP 27 2016

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 239 PM CDT Tue Sep 27 2016

Precipitation trends will continue to be the main forecast focus
tonight into Wednesday as a large nearly vertically-stacked system
slowly drops south through the Western Great Lakes.

The 19z MSAS surface analysis showed a strong area of low pressure
over eastern sections of Lake Superior with areas of high pressure
with over the Northern Plains or stretched from the Central Plains
east-northeast along the Ohio River Valley. Plenty of clouds
engulfed the Great Lakes as the radar mosaic picked up on a large
band of rain showers over northern sections of Minnesota and
Wisconsin, along with most of Upper Michigan.

As upper ridging builds from the Northern Plains northeast into
Western Ontario, this will force the nearly vertically-stacked
system to drop south from Lake Superior to southern sections of
Lake Michigan tonight. Even with the loss of daytime heating and
weaker instability, the strong cyclonic flow with individual
shortwaves rotating around the upper low, should keep fairly high
pops in the forecast through at least this evening. Do expect the
rain showers to become more scattered or isolated overnight,
especially from central to far northeast Wisconsin as the system
starts to move away. North-Central Wisconsin could see likely pops
through the night as winds veer from northeast to north and adds
lake enhancement to the synoptic conditions. Plenty of clouds
expected tonight, thus temperatures should be fairly uniform
throughout northeast Wisconsin. Look for readings to only drop
into the middle 40s far north, middle to upper 40s central/far
northeast Wisconsin and upper 40s to around 50 degrees east-
central WI.

This large system is progged to slowly move south-southeast into
northern sections of Indiana on Wednesday, thereby bringing a
weakening cyclonic flow to the forecast area. In addition, winds
are forecast to veer more to the northeast which would limit the
potential impact of lake effect across northern Wisconsin. While
the cloud cover is expected to stick around through much of the
day, anticipate precipitation chances to gradually diminish from
west to east with east-central WI holding on to a chance of
showers the longest. The pressure gradient will tighten once again
as the surface low pulls away, thus breezy conditions are expected
near the bay and Lake Michigan where gusts could approach 30
knots. Max temperatures are forecast to be a couple of degrees
either side of 60 which a little below normal for late September.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 239 PM CDT Tue Sep 27 2016

The upper system is forecast to move into the Ohio Valley Wednesday
night, taking any showers with it. A large surface high over southern
Canada should make it far enough south to make for dry weather
Thursday and Friday. The models both move the weakening upper
system from Kentucky to lower Michigan at the end of the week,
though the ECMWF continues to be the furthest west. This would
bring showers back to the forecast area for Saturday and part of
Sunday. Temperatures will be near normal tonight and Wednesday but
then average about five degrees above normal after that.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1016 PM CDT Tue Sep 27 2016

The main band of showers shifted south of the region this evening,
but another batch of lake-enhanced showers was moving into far
northern WI. Aside from the far north, expect only scattered
showers and patchy drizzle to persist across the area through
Wednesday morning.

Ceilings are generally expected to reside in the MVFR range
overnight into Wednesday as a large surface/upper low slowly
drops south from the Upper Peninsula into the Ohio Valley.
Ceilings are forecast to be in the IFR/LIFR range in north central
WI tonight into early Wednesday. A gradual improvement is expected
during the day on Wednesday, with VFR conditions possible by mid
to late afternoon. Partial clearing should occur Wednesday
evening.

Gusty northeast winds will develop on Wednesday, especially in
the Fox Valley and Lakeshore areas.
&&

.MARINE...
Issued at 239 PM CDT Tue Sep 27 2016

Conditions still exist for the potential of waterspouts Wednesday
morning due to the cold air aloft and cyclonic flow, thus have
continued this mention in the marine grids.

Another small craft advisory will probably be necessary on
Wednesday as winds increase from the northeast when the cyclone
shifts south of the area.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......RDM
AVIATION.......Kieckbusch
MARINE.........Kallas



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