Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 301003

Area Forecast Discussion
National Weather Service Green Bay WI
503 AM CDT Thu Mar 30 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 310 AM CDT Thu Mar 30 2017

Precipitation trends with respect to rain and snow amounts and
type, the forecast issue today into Friday morning. Overnight, an
initial and narrow west to east band of mostly rain mixed with
light snow associated with the mid level fgen band, stretched
across central Wisconsin into east central wisconsin. Little or no
snow observed with this band. This band continues to weaken early
this mornign as the mid level forcing continues to lift north
early this morning. Temperatures overall in the mid 30s across the
forecast area early this morning were producing primarily light
rain as well.  After a brief lull in the precipitation with this
first feature, next round of precipitation with the 850 MB WAA
working into southern Wisconsin and north of the 850 MB warm
front. More steady rains with embedded storms were noted near the
Wisconsin Illinois border. Progs overall weaken the 850 low today
into tonight, but this next round of precipitation will make a run
for northeast Wisconsin during the morning hours and into the
afternoon then gradually diminish from the west later this
evening. Forecast soundings still suggest a mix today into
tonight, and this next round of rainfall could bring down enough
cold air to turn to mostly snow with some accumulation this

More ideal air mass to support snow accumulation over far
northeast Wisconsin but perhaps too far north from the next round
of waa precipitation. But by then boundary layer temps may warm
enough later this morning to continue to support rain as the
primary. Will increase pops a tad over the far northeast today.
WPC shifted the better day 1 snow potential northward and north
of GRB today. There is an upper jet couplet region over eastern
wisconsin this morning to provide some forcing. Model QPF
forecasts are all over the place early this morning with the HRRR
with the higher qpf over east central Wisconsin early today. The
ECMWF delays the best precipitation until this evening with 0.25
inches over door county with a slower 850 low. GFS is quicker to
depart rain east while the NAM is somewhere in between.

System eventually departs late tonight into Friday morning
followed with a dry period Friday and into the weekend.

With the precipitation spreading over the area, will use a blend
of 3 hourly temperatures. Northern areas may break out of the
clouds or thin enough to produce higher max temps today as well
as Friday.

.LONG TERM...Friday Night Through Wednesday
Issued at 310 AM CDT Thu Mar 30 2017

Models remain consistent with the split flow pattern across
southern Canada and the CONUS into the middle of next week. The
northern stream will be weaker, more progressive with the southern
stream stronger and the main precipitation-maker. The first
southern stream system of interest could impact WI late this
weekend into early Monday, however the bulk of the better lift/
forcing appears to stay to our south. The next system toward the
middle of next week is forecast to take a slightly more northern
route across the central Plains, but there are timing issues among
the models, so confidence is fairly low with this system.
Temperatures appear to move above normal by this weekend and
remain that way through next Wednesday.

A modest ridge of high pressure is expected to move into the
western Great Lakes Friday night, bringing mostly clear skies,
light winds and seasonal temperatures. Look for mins to range from
the middle to upper 20s north-central, upper 20s to lower 30s
south. A very weak northern stream shortwave trough is expected to
move across northern sections of the Great Lakes on Saturday and
may brush some clouds across northern Wisconsin. Otherwise, high
pressure located just to our east should keep dry conditions in
place with mixed sunshine. This will allow max temperatures to
reach the middle to upper 40s near Lake MI (onshore component to
the wind), pushing middle 50s farther inland (especially over
central WI).

As the surface high pulls away, winds are forecast to veer to the
south Saturday night and attention turns to the next weather
southern stream system situated over the Plains. Anticipate clouds
to slowly increase through the night, but the air mass should be
too dry to support any precipitation. Min temperatures will settle
into the upper 20s north, lower 30s south. Even though the bulk of
the energy associated with the southern stream system (still over
the southern Plains) will remain well to our south on Sunday, the
onset of WAA coupled with the approach of another northern stream
shortwave trough, should bring our next chance for precipitation
to northeast WI by Sunday afternoon. Higher pops placed over our
southern counties and precipitation type would be all rain as max
temperatures again range from the middle to upper 40s near Lake
MI, lower to middle 50s elsewhere.

The chance for precipitation would then continue into Sunday night
as the northern stream shortwave moves into the Great Lakes
region. Depending on surface temperatures, we could be looking at
another mix of rain and snow (or all snow) later at night. Models
differ a bit on how fast this shortwave trough departs the region
headed into Monday with the GFS/CMC slower than the ECMWF. Prefer
to mention at least a small chance pop over the forecast area
through at least Monday morning and may even need to carry this
pop into Monday afternoon in the east. Mostly cloudy skies and
rain threat will keep temperatures in check with readings on
Monday in the upper 40s to lower 50s.

Models are now showing a break in the precipitation chances for
Monday night into Tuesday with weak ridging moving across the
Great Lakes. Therefore, have removed any precipitation that was
carried over from the previous forecast. As a result, have brought
more sun to Tuesday`s forecast and raised max temperatures over
inland areas into the lower to middle 50s, while again keeping
lakeshore areas in the middle to upper 40s.

The next southern stream system is poised to impact WI by the
middle of next week as it moves from the central Plains toward the
Great Lakes region. The GFS remains on the fast side of the
forecast envelope by already having precipitation overspread WI
Tuesday night. Other models prefer holding off any precipitation
until later on Wednesday. Expect the models to waffle a bit being
so far out in time, thus will follow the consensus solution which
brings a slight chance of light rain Tuesday evening, before
cooling temperatures begins to mix or change the type to snow.
Precipitation chances would then increase through Wednesday and be
in the form of light rain. Temperatures to remain fairly
consistent with more middle to upper 40s near Lake MI, lower to
middle 50s inland.

.AVIATION...for 12Z TAF Issuance
Issued at 503 AM CDT Thu Mar 30 2017

Ceilings will continue to fall to IFR levels over central and
northeast wisconsin as light rain mixed with light snow spreads
northward. A few of the snow showers may produce mvfr vsbys this
morning. Mainly MVFR ceilings expected further north with less
precipitation. Conditions expected to begin to improve later
tonight from west to east as the low pressure system departs




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