Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 191953
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
253 PM CDT MON SEP 19 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 253 PM CDT Mon Sep 19 2016

The main concern through Tuesday is convection this afternoon into
early evening.

An area of showers, associated with some upper level short wave
energy within a broad upper trough ahead of an approaching cold
front, was making its way across northern Wisconsin today. A few
thunderstorms also developed as the atmosphere destabilized during
the day. This area should be east of the area sometime around 00z.

A line of showers and thunderstorms developed in more unstable air
(mainly 500-1000 j/kg MUCAPE) in the vicinity of a surface trough,
but this line was moving out over Lake Michigan at 1930Z.

Another area of storms developed ahead of the cold front in
western Wisconsin and these storms were moving east this
afternoon, toward central and east central Wisconsin. The
strongest storms were in southwest Wisconsin and northeast Iowa,
where MUCAPES were mostly in the 1000-2000 j/kg range and there
was little or no CIN. Think that these will move a little south as
they move east and be out of the forecast area by 09Z.

High pressure moving into the region should keep the area dry with
few clouds and above normal temperatures overnight through
Tuesday.

.LONG TERM...Tuesday Night Through Monday
Issued at 253 PM CDT Mon Sep 19 2016

After a dry evening on Tuesday, an 850 mb warm front and
associated WAA will shift toward central WI, causing showers and
tstms to develop over mainly central and east central WI. The 850
mb/surface warm fronts will reside across the region on Wednesday
and Wednesday night, and provide the focus for precipitation
development over the entire CWA as short-wave energy and the RRQ
of an upper jet move through. With elevated instability in place
and PWATs increasing to 1.25 to 1.75 inches, heavy rainfall is
likely. The front is expected to sag back to the south Thursday
into Friday, so even though showers and tstms are possible,
especially in c/ec WI, the threat of heavy rain should diminish.
See the Hydrology section below for more details on the heavy
rainfall/flooding potential.

A short-wave trof and RRQ of an upper jet will pull through the
forecast area sometime during the Friday night to Saturday period,
and current chance pops may need to be raised with subsequent
forecasts.

Some weak ridging aloft may bring a slight lull in the pcpn later
in the weekend, but an approaching cold front will bring another
round of showers and thunderstorms Sunday night into Monday.

Above normal temperatures in the middle of the week will trend
toward near normal for the weekend.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1235 PM CDT Mon Sep 19 2016

VFR conditions prevailed across the vast majority of the forecast
area at 17Z. The main issues were an area of showers across
northern Wisconsin and a line/area of showers and a few
thunderstorms from central Wisconsin toward Door County. The
showers were in a broad upper level trough ahead of an approaching
cold front. Models showed this decreasing in coverage and moving
east-northeast out of Wisconsin. The showers and storms were in
the vicinity of a surface trough/wind shift where local
mesoanalysis graphics indicated 500+ j/kg MUCAPE. Model focus was
on central/east central Wisconsin later this afternoon as the cold
front moves into increasingly unstable air, and there is a
marginal risk for severe storms in an area southeast of a line
from near Kewaunee to east of Redgranite.

Have mentioned thunderstorms in the vicinity for a couple/few
hours at the start of the GRB, ATW, and MTW TAFs, but confidence
level was not high enough in exact timing and placement of any
storms later in the afternoon to include them. Also went with
showers in the vicinity at AUW, CWA, and RHI for a couple of hours
at the start of the TAF valid period.

Once the front clears the area dry and VFR conditions should
prevail through at least midday Tuesday.
&&

.HYDROLOGY...
Issued at 253 PM CDT Mon Sep 19 2016

Heavy rainfall will be concern during the middle of the week,
especially from Wednesday into Wednesday night, when models and
CIPS analogs show the potential for rainfall amounts of 1-3
inches. Looking at departures from normal precipitation for the
past 7 and 30 days, there are two parts of the CWA that are
significantly above normal. These areas include our northwest
counties, north of a line from Rhinelander to Florence, and far
southwest CWA, southwest of a line from Marshfield to Oshkosh.
These areas include large sandy soil regions, which can take a lot
of rain before flooding. One area of concern might be Wood and
western Marathon counties, where soils are heavier, and a couple
of our flashier rivers are located (but currently running low). It
is interesting to note that WPC has forecast QPF amounts near 4
inches through day 5 (Friday) in the western part of Wood and
Marathon counties, and our current QPF forecast through Thursday
calls for 2-3 inches. Will hold off on any hydro headlines at
this time, and attempt to get a better handle on where the axis of
heaviest rainfall will set up during the middle of the week.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Kieckbusch
AVIATION.......MG
HYDROLOGY......Kieckbusch



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