Area Forecast Discussion
Issued by NWS Green Bay, WI

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447
FXUS63 KGRB 270856
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
356 AM CDT Thu Apr 27 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 354 AM CDT Thu Apr 27 2017

No changes to headlines this morning. The main change to the
forecast was to trend toward more snow and less freezing rain,
based mainly on what`s been occurring on surface observations
early this morning. New grids sent and new ZFP should post
shortly. Complete discussion for this portion of the forecast will
follow a little later in the morning.

.LONG TERM...Friday Night Through Wednesday
Issued at 354 AM CDT Thu Apr 27 2017

Long-range models continue to show good agreement with the overall
mean flow consisting of a broad upper trough located over the
central CONUS, surrounded by upper ridges over the eastern Pacific
and western Atlantic. The main system of interest is forecast to
impact northeast WI starting Saturday night and could bring
precipitation of various types to the area through Monday night.
This system still looks strong with plenty of lift, forcing and
moisture to make for a messy forecast, especially at night as
temperatures cool and precipitation type issues arise.
Temperatures are expected to run below normal through the entire
extended forecast.

A wave of low pressure is forecast to ride along the recently
passed cold front across the southern Great Lakes region Friday
night. Models differ a bit on the exact track this wave takes with
the NAM farther north than the GFS/CMC/ECMWF. This is critical for
precipitation chances with the NAM bringing higher chance pops
into central/east-central WI, while the ECMWF keeps precipitation
well to our south. Will keep a low chance pop in the forecast for
east-central WI for Friday evening, but anticipate the bulk of any
precipitation to stay to our south. Otherwise, partly to mostly
cloudy skies to prevail with min temperatures in the middle to
upper 20s north, around 30 degrees central/far northeast WI and
middle to upper 30s east-central WI. Saturday is still looking
like a pleasant day across northeast WI as an area of high
pressure passes by to our north. This would keep a cool north-
northeast wind over the region, thus despite a mix of sun and
clouds, temperatures will remain below normal. Look for max
temperatures to range from the middle to upper 40s near Lake MI,
around 50 degrees north and lower to middle 50s south with the
warmest readings west of the Fox Valley.

Attention turns toward the southern Plains where a deep upper
trough to reside, accompanied by a strengthening area of low
pressure over southern MO/northern AR Sunday night. Increasing
southerly winds ahead of these features will not only draw copious
amounts of gulf moisture northward, but also begin to lift a
stalled boundary northward as a warm front (reaching central
sections of IL and IN by 12z Sunday). A surge of WAA into WI will
bring increasing precipitation chances, especially to central/
east-central WI after midnight. Depending on thermal profiles when
the precipitation arrives, either a rain/snow mix or all light
snow will be possible across central/northern WI. There might be a
minor snow accumulation, however the higher QPF amounts are
expected to be over east-central WI where the precipitation type
would remain all rain. Min temperatures to be in the lower 30s
north, middle to upper 30s south. The system is progged to lift
northeast on Sunday with the upper trough closing off into an
upper low over the central Plains and the surface low lifts north
into the Midwest. The warm front will remain to our south,
reaching northern sections of IL and IN by 00z Monday. Gulf
moisture to also continue flowing north with PW values surpassing
1.00" by Sunday afternoon. Persistent low-level WAA, coupled with
mid-level frontogenetical forcing, should bring a wet day to
northeast WI with any mixed precipitation or snow changing to all
rain by mid-morning. Max temperatures to only reach the middle 40s
over most locations due to thick clouds, precipitation and
blustery northeast winds.

This system still is expected to become vertically-stacked across
eastern IA/northwest IL/southwest WI Sunday night, before moving
northeast across WI on Monday. PW values around 1.25" across
eastern WI may bring locally heavy rainfall Sunday night and will
have to watch for both potential for flash flooding and river
flooding as ground conditions are already saturated from earlier
precipitation. The bigger question Sunday night will be
precipitation type over northern/central WI with a range from all
rain to all snow depending on how much warm air can get pulled
west by the approaching system. Models have shifted a bit farther
west, especially the CMC. This overall trend toward warmer would
lessen the risk of accumulating snow (other than the deformation
zone over MN/NW WI). Therefore, have adjusted precipitation type
more to a rain/snow mix over northern and parts of central WI
Sunday night. The rain showers will continue through Monday as the
system crosses the Badger state.

Wrap-around moisture and cyclonic flow to linger over the western
Great Lakes into Monday night, thus at least chance pops are
necessary. A shot of CAA pulled into WI should turn any rain to a
mix or all snow beginning late Monday evening through the
overnight hours. Deeper moisture to have pulled away by this time,
so any snow accumulations over the north appear minor at this
time. It may take until later Tuesday to finally get rid of the
effects of this system as weak surface ridging pushes into WI.
This surface ridging is expected to hold over the Great Lakes
through Wednesday, keeping any precipitation to our west or south.
Northwest flow aloft will keep temperatures below normal through
Wednesday.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1016 PM CDT Wed Apr 26 2017

Widespread IFR/LIFR conditions covered all but far eastern WI
late this evening, and ceilings should drop there within the next
few hours, as the cold front shifts through and rain develops.
Another area of significant precipitation will arrive overnight
into Thursday morning, and models are still indicating that it
will overspread our western counties late tonight into early
Thursday. While most of the region will see rain, our northwest
counties, including the RHI TAF site, will likely see a mix of
freezing rain, sleet and snow late tonight into Thursday morning,
as temperatures drop below freezing. It will be a close call for
AUW/CWA, as freezing precipitation may develop just to the west.
At the least, it appears that a rain/snow mix will develop there
Thursday morning. Some improvement in ceilings and visibilities
are likely on Thursday afternoon as the precipitation pulls out to
the northeast.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CDT today for WIZ005-010-011-
018.
&&

$$

SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......Kieckbusch



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