Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211135
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
635 AM CDT WED SEP 21 2016

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 342 AM CDT Wed Sep 21 2016

Many forecast concerns with this forecast package including
heavy rain the risk for severe storms.

Several rounds of showers and thunderstorms are expected during
the next 36 hours as a warm front slowly lifts north then stalls
across Wisconsin. This front will take advantage of deep moisture
as PWAT values climb to 1.5 to 2 inches across much of the
forecast area. Several shortwaves will track through the western
Great Lakes during this period, setting off several rounds of showers
and thunderstorms across the area through Thursday evening
bringing 2 to 3 inches of rain to the central and southern cwa,
with 4 inches or more possible across areas that see repeated
heavy rains. Given recent rainfall, deep moisture, and the
potential for several rounds of heavy rain will issue a flash
flood watch south of a line from Tomahawk, to Green Bay to
Kewaunee through Thursday evening as these areas stand the best
chance to see the most rainfall from this event.

Attention then turns to the severe weather potential during this
period. Despite little in the way of instability, current activity
tracking across the southern cwa has a history of producing some
wind damage. Given the time of day this activity should dissipate
as it heads east, however it has so far defied the odds so
anything is on the table at this point. Later today instability is
expected to rise to 1 to 2 J/g across the forecast area as another
round of showers and thunderstorms is expected to track through
the western Great Lakes. There is a marginal risk for these
additional storms to become severe during the afternoon and
overnight hours, with damaging winds and large hail being the main
threat.

By Thursday the severe threat should be more muted, as
instabilities are limited to a few hundred J/kg across the
forecast area. However long skinny cape profiles as well as
continued high PWAT values will bring a continued risk for heavy
rains to the forecast area.

.LONG TERM...Thursday Night Through Tuesday
Issued at 342 AM CDT Wed Sep 21 2016

Main concern for this period will be the frontal boundary that
should slowly push southward Thursday night through Friday
night, and then returns slowly north over the weekend. Late
this weekend into early next week, a slow moving cold front could
bring another round of heavy rain to the upper Midwest.

Showers and a few thunderstorms are likely Thursday night into
central and northeast Wisconsin with only slight chances of
showers across the north. The front will continue to sag slowly
southward late Thursday night and Friday. This should allow for
the north to dry out. Will have to keep small chances of showers
and perhaps a thunderstorm across the south due to the close
proximity of the front. The front will slowly lift north as a warm
front over the weekend, bringing chances of showers and storms.

Looking ahead to Sunday into early next week, the models are
showing a slow moving cold front that could take a day or two to
clear the region. Moist southerly flow should transport abundant
moisture should bring another round of rain, which could be heavy
at times.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 635 AM CDT Wed Sep 21 2016

A round of showers and thunderstorms continues to slowly move out
of east-central Wisconsin early this morning. Doppler radar and
model trends show a brief break in the action once this complex
tracks east, with additional activity expected later this
afternoon and into the overnight hours as a surface front becomes
stationary across Wisconsin. Cigs and vsbys are expected to lower
later tonight as deeper moisture arrives with additional activity
lasting into the overnight hours.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday evening FOR WIZ018>020-030-
031-035>040-045-048>050.
&&

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......Kurimski


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