Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 201738
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1238 PM CDT TUE SEP 20 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 350 AM CDT Tue Sep 20 2016

Recent rainfall combined with clear skies and light winds has led
to dense fog across much of central and east central wisconsin
during the early morning hours. Farther north conditions were much
better given these areas did not get a secondary push of rainfall
during the evening hours. To the east a bit higher winds have
kept the fog at bay, however patchy dense fog is still possible at
times but this should be transient in nature. The dense fog is
expected to impact the morning commute, before dissipating later
this morning by 9 am as sunrise causes mixing in the lower layers
of the atmosphere as high pressure tracks through the western
Great Lakes. This high will provide dry weather with a few clouds
and above normal temperatures during the daytime hours.

Later tonight a warm front is slated to move north into southern
Wisconsin, causing showers and thunderstorms to develop north of
the boundary across central and east central Wisconsin. This
frontal boundary will remain stationary across southern Wisconsin
into Wednesday, with a continued chance for showers and
thunderstorms across the entire area. Rain chances look better on
Wednesday as instability values climb to around 2 J/g across
central and east central Wisconsin Wednesday afternoon as PWAT
values climb to 1.5 to 1.75 inches, increasing the threat for
heavy rain.

.LONG TERM...Wednesday Night Through Monday
Issued at 350 AM CDT Tue Sep 20 2016

It appears that a heavy rain event is setting up this week as a
front stall across the state. Complexes of thunderstorms moving
along the front may actually push the front further south than the
models indicate tonight, thus some uncertain exists with the axis
of heavy rain will set up later this week. It still appears that
portions of central/north-central into northeast Wisconsin could
see 1 to 3 inches of rain, with amounts over 4 inches possible
towards Wood, Portage and Marathon Counties. Will continue the ESF
product for now. Coordinated with NWS La Crosse on holding off
on a Flood/Flash Flood watch. Could be some stronger storms
Wednesday evening and possibly on Thursday if there is a break in
the clouds.

The front should sag south late Thursday night and Friday and may
give a brief break in the rate. The front is expected to head
north as a warm front later Friday night and Saturday. Beyond
that, there could be a break in the chances of rain for a period
of time Saturday night into Sunday until cold front approaches
from the west. Some significant differences Sunday night and
Monday with timing of the cold front moves across the region. Will
follow previous forecast for these two periods. Above normal
temperatures early in the period should return close to normal
this weekend.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1238 PM CDT Tue Sep 20 2016

VFR conditions are expected this afternoon through the evening
with surface high pressure over Wisconsin moving east. Not great
confidence in the forecast for the latter half of the TAF valid
period due to model differences in their precipitation forecasts.
The 12Z NAM QPF seemed overdone, though onset of rain may not be
too bad. An attempt was made to use a compromise among the NAM,
GFS, ECMWF, UKMET, and Canadian. Still, mainly VFR tonight except
lower visibilities in any showers/thunderstorms. Expect MVFR
visibilities in fog during the morning. There are also some rain
chances for central and north central Wisconsin.
&&

.HYDROLOGY...
Issued at 350 AM CDT Tue Sep 20 2016

Periods of heavy rain are likely from late Tuesday night through
Thursday night, especially across central/north-central into
portions of east-central and northeast Wisconsin. Latest model
runs continue to show differences in where the axis of heavy rain
will set up, but it appears the greatest of risk for heavy rain
and potential flooding would be across central Wisconsin including
Marathon, Wood, and Portage Counties. WPC graphics continue to
show 3 & 5 day rainfall totals over 4 inches in this region.
Decided to hold off on flash flood/flood watch due to the
transient nature in where the axis of heavy precipitation will set
up. It is possible the later rounds of storms could produce heavy
rains further south than what the models indicate.

with
additional chances of rain from Friday into early next week.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......MG
HYDROLOGY......Eckberg



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