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Area forecast discussion 
National Weather Service Green Bay WI
244 PM CDT Friday Sep 4 2015

Forecast discussion for routine afternoon forecast issuance

issued at 244 PM CDT Friday Sep 4 2015

Warm and humid through most of the Labor Day weekend...with a
round of thunderstorms Sunday night into Monday morning.

Amplitude of the large scale pattern will soon peak...with a fairly
deep trough along the West Coast and a ridge from the middle-Mississippi
Valley northeastward to Ontario. Next week the pattern will settle back into
a lower amplitude regime with ridges near the coasts and a trough

Warm and humid conditions will persist early as long as the upper
ridge dominates the area...then temperatures should drop back
closer to seasonal normals next week. The main opportunities for
precipitation will be with cold front crossing the area Sunday
night into Monday...and with a wave ridging eastward along the front
next week. The result will probably be at or above normal precipitation for most of
the area...with significantly higher totals in any areas
repeatedly affected by storms.

Short term...tonight and Saturday
issued at 244 PM CDT Friday Sep 4 2015

The chance for precipitation Saturday becomes the main focus for the
short term...with more fog possible tonight.

Current mesoanalysis and water vapor imagery showed a fairly
progressive but weakening shortwave over the Dakotas and
Minnesota riding along the edge of the main upper level
ridge...with showers and thunderstorms developing in response to
this piece of energy. Further east of Wisconsin...ridging
continued to dominated the weather pattern. This ridge should hold
through the night...with fog development again possible. Mixing
layer winds were on the stronger side so dont think visibilities
will crash...but low stratus should still plague much of NE
Wisconsin...with the worst conditions in north central Wisconsin.
Any fog should lift through Saturday morning...much like we have
seen the past few days.

The question then becomes which feature will win on Saturday...the
Main Ridge or the noted system as is moves up and over the ridge
axis. Forecast models are all over the place and show little could not add much detail with confidence on precipitation
timing or coverage Saturday. Tried to time probability of precipitation with the best
forcing and the arrival of better warm air advection...however lift should be
broad and weak. Ended up with slight chance probability of precipitation for much of our
area. While couldnt add better timing or placement for
Saturday...confidence is high that whatever does develop should be
isolated and low impact...and shouldnt ruin the entire day.

Saturday will be warmer than today...and with increasing dewpoints
it will certainly feel like Summer.

Long term...Saturday night through Friday
issued at 244 PM CDT Friday Sep 4 2015

Main forecast issue is timing of precipitation with the frontal system
crossing the area during the latter half of the Holiday weekend.
There is still some uncertainty concerning whether or not
convection with shortwaves riding around the upper ridge will affect the
area during the early part of the weekend. Stayed close to previous
forecast in this regard...with low-chance probability of precipitation across the north.

Timing of the main precipitation band with the front is a little slower
than yesterday...and would not be surprised if a little additional
slowing occurs. Structured forecast with likely probability of precipitation across the west for
late Sun night...but tapered back to chance in the far east. Stuck with
only high chance probability of precipitation in the east Monday timing of frontal passage
may only support scattered coverage as the front crosses that area.

Used blend of top performing guidance products for temperatures...with
some adjustment to account for cooler temperature Lakeside. Glerl
lake surface water temperature analyses indicated that the very
cold water that upwelled along the western shore has warmed...though
it is still cool enough to necessitate having cooler maximum temperatures
near the lake.

Medium range models pretty much agree that front will slow as it pushes
S of the forecast Ara and a sig WV will ride eastward along the boundary
early next week. Not unexpectedly at that time range...details of
placement/timing of the greatest precipitation differed among the models.
The chance probability of precipitation supplied by the extended forecast initialization
grids seemed adequate for now...with no sig changes necessary.

Aviation...for 18z taf issuance
issued at 1107 am CDT Friday Sep 4 2015

Once any lingering broken MVFR clouds scattered out in central and
east central Wisconsin...VFR conditions are expected this
afternoon into early tonight with light winds. Overnight...much
like the past few days...fog should develop as skies become
mostly clear and winds go light. Stronger mixing at the boundary
level should keep visibilities in the IFR range...however IFR to
LIFR clouds may develop. Heading into Saturday morning...the fog
and low ceilings should improve by late morning...with VFR conditions
and continued light winds after that.

Grb watches/warnings/advisories...


short term.....Allen
long term......skowronski

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