Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 250359
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1059 PM CDT SAT SEP 24 2016

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 255 PM CDT Sat Sep 24 2016

Main forecast concern to be the rainfall amounts associated with
the next weather system mainly on Sunday. Plenty of moisture to be
available and with saturated grounds and rivers running high over
central WI, flooding could be a problem.

The 19z MSAS surface analysis showed an area of high pressure
stretched from eastern Ontario south-southwest across Lower MI. An
area of low pressure was located over southwest ND with a cold
front arcing southward over the Plains. Radar mosaic picked up on
showers and thunderstorms just ahead of the cold front. Influx of
drier air had eaten away at the clouds over eastern WI this
afternoon with more clouds just to the west.

Generally quiet conditions are expected for the bulk of tonight as
the high pressure edges eastward into the Eastern Great Lakes.
Focus then quickly shifts to the west where a strong shortwave
trough to move into the Plains and will be preceded by the cold
front that is forecast to reach western sections of MN and IA by
12z Sunday. Southerly winds ahead of this system will pull gulf
moisture northward with PW values climbing into the 1.25 to 1.75
inch range. Showers, with embedded thunderstorms, are forecast to
to move ahead of the frontal boundary and be on the verge of
reaching central WI toward daybreak. Min temperatures to range
from the lower 50s far northeast WI, to around 60 degrees south.

The mid-level trough will push into the Upper Midwest on Sunday,
while the cold front moves into Western WI by 00z Monday. Expect
to see a band of showers to precede the front across the forecast
area and with PW values at 1.5 to 2.0 inches (or 250 percent of
normal), there could be some locally heavy rain possible.
Instability is marginal, but with 0-6km bulk shear at 25-30 knots,
anticipate at least a chance of thunderstorms across northeast WI,
which would add to the precipitation totals. After collaboration
with ARX and MKX, have decided to issue a flash flood watch for
Wood, Portage and Waushara counties on Sunday due to heavier rains
from earlier in the week. This band of showers is progressive in
nature, however with grounds saturated and rivers still high, it
would not take much rain to generate flooding. Sunday could also
be a bit breezy, especially over eastern WI before the
precipitation arrives. Max temperatures are expected to be in the
middle to upper 60s north-central, lower 70s east-central WI.

.LONG TERM...Sunday Night Through Saturday
Issued at 255 PM CDT Sat Sep 24 2016

The models forecast the upper trough that moves into northern
Wisconsin and Upper Michigan late Sunday night to deepen and
become a closed upper low near Sault Sainte Marie by Monday night.
It then slowly drops south across lower Michigan Wednesday. As it
does so, a fairly strong surface low moves from east of Lake Winnipeg
towards Lake Huron. This should result in windy and cool conditions
Monday and Tuesday with scattered showers and even some lake
enhanced showers over far northern Wisconsin. Dry weather should
return Wednesday and probably last through at least Saturday.
Temperatures will start out around five degrees below normal
Monday and Tuesday but rise to seasonal normals by the end of the
week.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1055 PM CDT Sat Sep 24 2016

MVFR conditions were spreading back into central and north central
WI late this evening, and are expected to push into eastern WI
later tonight into early Sunday. Flight conditions will deteriorate
to IFR/LIFR in central and north central WI late tonight, as deeper
moisture and precipitation arrives.

A cold front and upper level trough will impact the Western Great
Lakes overnight through Sunday. Look for showers and a few
thunderstorms to move from west to east across the region, with
the heaviest rainfall occurring over central and north central WI
in the late morning to mid-afternoon, and over eastern WI from
mid-afternoon through early evening.

Flight conditions should improve after the cold front moves
through in the late afternoon and early evening. Gusty south winds
in advance of the front will become southwest to west after the
frontal passage.
&&

.MARINE...
Issued at 255 PM CDT Sat Sep 24 2016

Gusty west to northwest winds are expected Monday into Tuesday.
Gale force gusts are possible at times Monday afternoon into
Tuesday morning across the coastal waters of northern Door County.
Winds should begin to decrease later Tuesday afternoon and Tuesday
night.
&&

.HYDROLOGY...
Issued at 255 PM CDT Sat Sep 24 2016

Another round of showers, with some embedded thunderstorms, can be
expected late tonight through Sunday as a cold front moves through
the region. Even though rainfall amounts are forecast to be under
an inch with this system, parts of central Wisconsin are still
recovering from very heavy rains from earlier in the week. PW
values are forecast to approach 2.0 inches which is nearly off the
charts for late September, thus locally heavy rainfall is possible
on Sunday. Therefore, a Flash Flood Watch has been posted for
Wood, Portage and Waushara counties.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 4 AM CDT Sunday through Sunday evening
FOR WIZ035-036-045.
&&

$$

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



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