Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 170954
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
454 AM CDT Mon Apr 17 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 451 AM CDT Mon Apr 17 2017

Forecast challenge today will be cloud trends and temperatures as
backdoor cold front drops south across the forecast area this
morning.

Latest GOES16 3.9 imagery clearly shows leading edge of low
stratus quickly dropping southwest across northeast Wisconsin.
These clouds are following in the wake of a backdoor cold front
that has just pass south of the Green Bay area. Southern edge of
stratus deck extends from roughly Green Bay to Eagle River.
Temperatures behind the front falling into the middle 30s across
far northern and northeast Wisconsin. Also some patchy light
drizzle or flurries further north into central Upper Michigan.

Short term HRRR and RAP generally in agreement with continuing to
push backdoor front southwest during the day. Although both of
these models are slower than reality with the passage of the front
through the GRB area, will go with RAP given its faster movement
overall. Thus, expect backdoor front to be located generally along
a line from about OSH to Antigo by around 16Z or so. Would also
expect stratus deck to also make its way southwestward across most
of the Fox Valley during the morning. Will feel rather chilly and
blustery this morning with northeast boundary layer flow off Lake
Michigan, broken clouds and temperatures remaining generally in
the 40s northeast of the front. Will be a rather stark temperature
contrast from southwest to northeast with temperatures over
central sections still managing to climb close to 60 F, while
over the far northeast...temperatues will likely remain in the
middle to upper 40s with perhaps some patchy light drizzle and fog
this morning.

Meanwhile radar indicates a narrow band of very light returns
quickly moving across central Wisconsin in association with some
mid-level instability and weak shortwave impulse. Have not seen
much of anything reaching the ground. Do not expect more than
a very brief light shower or sprinkles during the morning hours.
Further north...shortwave trough in concert with aforementioned
frontal boundary will provide a bit more forcing for some
scattered light rain showers generally north of a Marinette to
Rhinelander line during the day. Could also be mixed with a
little snow near the upper Michigan border at times this morning.

By early evening shortwave trough should be well east of the
forecast area as upper heights begin to increase over the western
Great Lakes and another surge of somewhat drier air work east
across the forecast area during the evening. Broken clouds should
gradually diminish this afternoon with generally partly cloudy
skies especially over central sections of the forecast area. Think
clouds will be a bit more stubborn over eastcentral and northern
Wisconsin within cool NE boundary layer flow. Temperatures will
range from the upper 20s far north to the upper 30s over southwest
sections overnight.

After a partly sunny and cool start on Tuesday, clouds will
rapidly be on the increase during the morning as potent shortwave
begins to impinge on the western Great Lakes. Robust warm
advection ahead of approaching cold front, along with modest mid-
level instability will lead to a band of showers and perhaps some
embedded thunder reaching central Wisconsin by around mid-
morning, then eastern sections shortly after midday or so. Best
chance for some thunder will be generally southwest of the Fox
Valley Tuesday afternoon. Despite increasing clouds and shower
activity, temperatures should be able to rebound into the 60-65
degree range generally south of Highway 29 Tuesday afternoon with
50s elsewhere. Given rapid progression of this system, do not
expect precipitation amounts to to exceed 0.25 inch over most
areas, thus precipitation should not have appreciable impact on
current river levels.

.LONG TERM...Tuesday Night Through Sunday
Issued at 451 AM CDT Mon Apr 17 2017

Focus for this portion of the forecast revolves around precip
chances and types as a result of a strong cyclone moving across the
region during the Wednesday night through Thursday period.  Some
timing and track differences noted in the latest medium range model
runs.  Have a slight preference for the ecmwf over the gfs.

Tuesday night through Wednesday night...Low pressure will travel
northeast across Lake Superior and drag across a cold front the
eastern half of Wisconsin on Tuesday night.  Until this front clears
the state, will have a chance of showers over eastern WI.  Some low
clouds could stick around over far northern WI overnight, but the
rest of the area should see some clearing take place with occasional
areas of cirrus passing overhead.  Clouds will increase and lower
more quickly on Wednesday as the next system works east across the
Plains.  A large area of fgen north of the surface low track will
start to bring in precip mainly into central and east-central WI
during the afternoon.  As low pressure moves across northern IL,
should see precip pick up in intensity Wednesday evening with
lighter precip continuing overnight.  Precip type will become a
concern late Wednesday night over northern WI as colder air is
pulled in from the north.  The gfs is colder than the ecmwf, most
likely due to its stronger solution.  Boundary layer temps will be
key in this case, and dont have enough confidence to remove the
mention of accumulating snow from the HWO.

Rest of the forecast...Light precip will continue on Thursday with
the deformation zone of the system passing overhead.  Potential for
snow across northern WI will remain present for the morning until
boundary layer temps warm.  Precip will exit Thursday evening as
high pressure builds into the region.  This surface high is then
projected to hang around through the weekend with the state located
between systems north and south of the region.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1124 PM CDT Sun Apr 16 2017

In addition to patchy mid level clouds passing over
tonight, patchy MVFR/IFR cigs and vsbys over the northern Great
Lakes region may work south overnight in the wake of a weak cool
front. These MVFR/IFR cig may expand overnight before slowly
dissipating later Monday morning into the afternoon.
&&

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

$$

SHORT TERM.....ESB
LONG TERM......MPC
AVIATION.......TDH



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