Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 151052

Area Forecast Discussion
National Weather Service Green Bay WI
552 AM CDT SAT OCT 15 2016

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 331 AM CDT Sat Oct 15 2016

The main forecast concerns include precipitation and thunder
chances through tonight, fog potential late tonight into Sunday
morning, and temperatures.

A very mild and moist air mass continues to flow into the region
early this morning, due to gusty south winds in advance of a cold
front in the eastern Dakotas. Temperatures were in the lower to
middle 50s across most of the forecast area, close to normal
highs for this time of year. Several locations in western WI were
in the lower 60s. Stratus clouds were working their way east
across the region, and should overspread the Fox Valley/Lakeshore
areas between 12z-15z. No drizzle has been reported upstream,
but models continue to support a chance over north central WI
toward daybreak.

Have backed off on precipitation chances a bit this morning, with
only a chance of drizzle over north central and central WI until
16z-18z, when moisture may deepen enough to support scattered
light rain or showers. A short-wave trof will combine with the
approaching cold front and some weak elevated instability to
produce scattered showers and isolated thunderstorms this
afternoon. Will carry likely pops in east central WI this evening,
as PWATs increase to around 1.5 inches ahead of the front.
Precipitation chances will taper off from northwest to southeast
tonight into early Sunday as the front moves through. Partial
clearing in the wake of the front, combined with boundary layer
winds decreasing to 5 to 10 kts and lingering low-level moisture,
should lead to fog development overnight into Sunday morning. MOS
guidance is adamant that dense fog will develop, but confidence is
not high enough to mention dense fog in the forecast right now.
Will likely add a mention in the Hazardous Weather Outlook,

Despite stratus overspreading the region today, advection should
boost high temperatures into the lower to middle 60s. After a very
mild evening in the upper 50s to middle 60s, temperatures should
fall into the upper 40s to lower 50s across the northwest part of
the forecast area, in the wake of the cold front. There is some
uncertainty concerning high temperatures on Sunday, as morning fog
and low clouds could slow warming. decided to stick with the model
blend for now, with highs in the mid to upper 60s, but these may
need to tweaked down a few degrees.

.LONG TERM...Sunday Night Through Friday
Issued at 331 AM CDT Sat Oct 15 2016

An energetic flow will continue to slam the Pacific Northwest
through Tuesday before the mean Eastern Pacific upper trough
begins to transition eastward across the CONUS. This upper trough
is expected to reach the central CONUS by mid-week before the
models differ on how far east to take the trough. For northeast
Wisconsin, the weather will be unsettled/mild through at least
Monday night/Tuesday, then shift to a cooler/drier pattern mid to
late week. Main forecast issue to remain timing of individual
precipitation events, especially from Sunday night through

Models are consistent in cranking up a 50 knot southwest low-level
jet over the central CONUS Sunday night which will lift a stalled
frontal boundary northward as a warm front through almost all of
Wisconsin by daybreak. Lift associated with the warm front and
good moisture transport should allow for a band of showers to move
across the forecast area, accompanied by elevated thunderstorms.
Locally heavy rain and brief gusty winds could occur with any of
these storms, but severe looks unlikely with only marginal
instability. Min temperatures to be in the middle to upper 50s
north, upper 50s to lower 60s south.

Shower/thunderstorm chances will continue through Monday as a
modest cold front moves across the Upper MS Valley into the
Western Great Lakes. At least one wave of low pressure is forecast
to ride northeast along this front which would provide additional
focus for precipitation along with lift from the cold front.
Furthermore, models hint at a mid-level shortwave to lift
northeast within the southwest mean flow aloft to add forcing for
precipitation development. Despite all the clouds/precipitation in
our vicinity, Monday still looks like the warmest day of the
extended forecast with max temperatures to range from the middle
to upper 60s north-central, lower to middle 70s east-central
Wisconsin (away from Lake MI).

Unsettled weather persists over the area Monday night as another
surface wave moves along the slow-moving cold front which is only
expected to reach central or eastern Wisconsin by 12z Tuesday. In
addition, a more prominent mid-level shortwave trough will be
moving into the Upper MS Valley/Midwest, thus expect at least
chance pops across the forecast area. Better jet support to be
located over northern sections of the Great Lakes, so have placed
higher pops over northern Wisconsin. Min temperatures will remain
mild with lower 50s north, middle to upper 50s south. The cold
front to languish over the Great Lakes right into Tuesday,
although better dynamics/jet energy to be pulling away from the
region. Precipitation chances appear to again favor northern
Wisconsin and points east on Tuesday, although confidence on how
this will all play out is somewhat low. Tuesday will be a
transition day with respect to a gradual, but steady drop in
temperatures for the rest of the work week. Max temperatures on
Tuesday to range from around 60 degrees north-central, to the
upper 60s east-central Wisconsin.

It is still looking like a break in the precipitation chances for
Tuesday night/Wednesday as the main forecast focus shifts to the
eastward moving shortwave trough pushing toward the central CONUS
by 00z Thursday. Under generally partly cloudy skies, max
temperatures on Wednesday to be in the 50-55 degree range north,
55-60 degree range south (which is closer to normal).

Forecast becomes much more uncertain for the latter part of the
work week as the models have a serious disagreement with the
handling/strength of this mid-level trough. The ECMWF remains
progressive with the trough over east-central NOAM on Thursday,
while the GFS/CMC dig additional energy into the base of the
trough, thereby only having the trough reach the central CONUS on
Thursday. This difference becomes more apparent by Friday with the
ECMWF`s trough placement over the eastern CONUS versus the GFS/CMC
trough placement just reaching the east-central CONUS and
attempting to close off into an upper low near the Mid-MS Valley.
Needless to say, precipitation trends vary wildly with the ECMWF
producing hardly any precipitation, while the other models have
increasing precipitation chances by Thursday night/Friday. Have
followed the model consensus solution for now, which does bring a
small chance of light rain to east-central Wisconsin on Friday.
Max temperatures for both Thursday and Friday should fall to
slightly below normal levels.

.AVIATION...for 12Z TAF Issuance
Issued at 534 AM CDT Sat Oct 15 2016

MVFR cigs have overspread north central, central and parts of far
northeast WI early this morning, and should reach the Fox Valley
and lakeshore areas between 12z-15z. Ceilings have not dropped
into the IFR category at our western TAF sites, as was expected,
but a large area of IFR cigs was approaching from northeast IA,
far southeast MN and far southwest WI. In addition, drizzle has
been slow to develop. Current expectation is for moisture to
deepen enough for precipitation development in nc/c WI between
16z-18z, and in eastern WI during the late afternoon. With weak
elevated instability arriving in the afternoon/evening, and the
approach of an upper level disturbance and associated cold front,
there will be a small chance of thunderstorms over the forecast
area. However, confidence is not high enough to mention at the
TAF sites at this time.

Partial clearing will occur across north central, and parts of
central and northeast WI in the wake of the cold front late
tonight. This clearing, combined with lingering moisture and
decreasing winds, should lead to areas of fog overnight. The
fog may become dense in some areas.


Issued at 331 AM CDT Sat Oct 15 2016

A gale warning remains in effect for the central bay of Green Bay
and the nearshore waters of Lake Michigan north of Sturgeon Bay
into tonight. For the southern bay of Green Bay and the nearshore
waters of Lake Michigan south of Sturgeon Bay, a small craft
advisory is in effect. The gale warning has been marginal so far,
with gale force gusts (and 10 ft waves) only reported at the mid-
lake buoy. However, gusts as high as 33 kts have been observed at
Sister Bay, and they may reach gale force as winds become south-
southwest, which is more favorable for coastal convergence.

The gale warnings will likely need to be transitioned to small
craft advisories this evening, as wind gusts ramp down. Waves
will likely not drop below 4 ft until around 09z/Sun on Lake



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LONG TERM......Kallas
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