Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 222340
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
640 PM CDT THU SEP 22 2016

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 223 PM CDT Thu Sep 22 2016

A break in the excessively wet weather, but temperatures remaining
near or above seasonal normals.

Currently on the large scale, strong Pacific jet splits near the
West Coast before merging back together in the Great Lakes region.
The pattern will be slowly progressive, especially early in the
forecast period. Ridging building northeast from the eastern
Pacific will force the location of the split eastward into the
Plains by the weekend. Thereafter, the evolution of the flow
regime becomes uncertain as the medium range models offer varying
ideas on the handling of the remnants of the current southern
stream upper trough. That uncertainty will impact precipitation
chances during the latter part of the forecast period.

Temperatures are expected to remain near to modestly above
seasonal normals through most of the the period, though they could
tail off late. Shower chances will continue the next couple days,
especially across the southern part of the forecast area. But
rainfall amounts should remain on the light side. Precipitation
chances during the middle to latter part of the period will depend
on the evolution of the current southern stream upper trough now
over the western CONUS, and thus are a low-confidence aspect of
the forecast. The best estimate is that rainfall totals for the
next 7 days will end up AOA normal, though at this point amounts
do not look excessive.
&&

.SHORT TERM...Tonight and Friday
Issued at 223 PM CDT Thu Sep 22 2016

The latest RAP analysis and satellite/radar imagery show a nearly
stationary surface cold front stretching from west-central WI to
near Wausaukee early this afternoon.  Scattered morning showers died
off along the boundary by midday, but the hi-res models continue to
indicate that a few showers will be possible over east-central and
far northeast WI and within a pwat axis through the rest of the
afternoon. Not convinced that will occur since there is little to no
instability, but left a small chance just in case.  Observations
also indicate the presence of some drizzle over far northwest
Wisconsin within a band of low clouds behind the front.  Some of
this drizzle could move into Vilas county later this afternoon.  As
the front finally makes a move southward tonight, small precip
chances and cloud cover are the main forecast concerns.

Tonight...The cold front will finally move south across central and
northeast WI this evening, and into southern WI overnight.  Position
of the pwat axis and hi-res models indicate that east-central WI
could see a shower or two early in the evening before the front
exits the forecast area.  But will leave a slight chance across the
south in case the front is slower to exit than progged.  Otherwise,
should see widespread cloudiness linger behind the front per
satellite imagery.  A developing northeast breeze should keep the
boundary layer churned up to limit fog potential even after all of
the rainfall.  Lows falling to near 50 in the north to near 60 in
the south.

Friday...The cold front will settle over far southwest Wisconsin and
northern Illinois.  A band of low clouds are expected to remain
behind the front, which should keep central and east-central WI more
cloudy than over northern WI, where northeast winds will push in
drier air.  Cannot rule out a few showers over central and east-
central WI in a region of modest mid-level fgen.  Because of more
sunshine, northern WI could be as warm or warmer than locations
further south.  Will go with highs mostly in the mid 60s.

.LONG TERM...Friday Night Through Thursday
Issued at 223 PM CDT Thu Sep 22 2016

Weak isentropic lift will begin spreading back across the area
Friday night. That seems worthy of having chance PoPs expand
northeast across most of the area during the night, though with
limited instability opted to leave thunder out of the forecast.

Though confidence in precipitation forecast for the rest of the
period is probably lower than normal, leaned toward the ECMWF for
PoPs. The 12Z EC was fairly consistent with its previous run, and
exhibited decent consistency with the GFS ensemble mean. That
resulted in a prolonged period of chance PoPs as the upper trough
crosses the area. The best chance for rain looks to be Sunday and
Sunday night, though that could easily chance in later forecasts.

No significant changes were necessary to the extended forecast
initialization grids based on a broad blend of guidance products.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 639 PM CDT Thu Sep 22 2016

A frontal boundary will continue to sag south tonight. A few
showers are possible along this front tonight into Friday over the
south half of the state.  There is a chance for a light shower or
sprinkle across the north tonight as a short wave slides over the
northern Great Lakes. Anticipate MVFR then a period of IFR cigs
will become more dominate tonight with patchy fog possible across
central and East Central Wisconsin. Drier air pouring in from the
north should improve northern and Northeast Wisconsin to VFR
conditions Friday morning as high pressure drifts over the
northern Great Lakes Region.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......TDH



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