Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 260855
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
355 AM CDT Wed Apr 26 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 352 AM CDT Wed Apr 26 2017

The complete discussion for this portion of the forecast will
follow a little later. Temperatures tonight will be right at the
threshold to support icing in far north-central Wisconsin. A
deviation of even a couple degrees from the current forecast will
greatly impact the potential for icing. Will defer to the day
shift to make the final decision on an advisory.

.LONG TERM...Thursday Night Through Tuesday
Issued at 352 AM CDT Wed Apr 26 2017

After a break in the precipitation chances at the end of the week,
attention will be focused on the Sunday-Monday time frame as a
strong, nearly stacked system to move from the southern Plains
through the Great Lakes region. Depending on the eventual track of
this system, locally heavy rains may occur, accumulating snow may
occur or a mix of rain/snow may occur. Even after this system
departs, there are questions with another weaker system to
possibly approach toward the middle of next week. Temperatures are
expected to run below normal through the extended forecast.

An initial system will continue to lift north farther into Ontario
Thursday night, leaving very weak surface ridging extended from
the northern Plains to the Great Lakes. Expect skies to at least
become partly cloudy with winds gradually diminishing into the 5
to 10 mph range. The departed system will pull colder air into the
region with 8H temperatures down to the zero to -8C range by 12z
Friday. This would send min temperatures into the middle 20s
north-central WI, lower 30s east-central WI. Dry weather would
continue into Friday, however there is a small threat of light
rain into central/east-central WI Friday afternoon as a weak
surface wave moves along an old frontal boundary, a mid-level
shortwave ejects northeast out of the broad central CONUS upper
trough and WI to reside in the left exit region of the upper jet
for additional lift. Meanwhile, northern WI will remain partly
cloudy through the day, but still cool by late April standards.
Look for max temperatures to be in the upper 40s to around 50
degrees north, lower to middle 50s south.

The light rain chances will linger into Friday evening as the
surface low/shortwave move toward the eastern Great Lakes. High
pressure is then forecast to build into WI later Friday night and
allow skies to become partly cloudy. Winds are forecast to shift
to the north-northeast and continue to funnel cool air into WI.
Min temperatures to range from 25-30 degrees north, lower to
middle 30s south. High pressure centered over western Ontario will
continue to send a cool, dry northeast winds into northeast WI on
Saturday and help to at least temporarily stall precipitation from
returning to the area. There is no doubt that Saturday will be the
nicer of the two weekend days, although clouds are expected to
increase through the day and max temperatures to be about 10 to 15
degrees below normal.

Attention then turns toward the southern Plains where a strong
upper trough to reside with a strengthening area of low pressure
starting to lift north into the mid-MS Valley Saturday night. A 50
knot southerly low-level jet ahead of this system will not only
quickly pull gulf moisture northward toward the Great Lakes, but
also lift a warm front north into northern IL by 12z Sunday. A
push of WAA into southern WI will allow for precipitation to
steadily lift north with precipitation chances increasing,
especially over central/east-central WI after midnight. Residual
cooler air over northern WI and parts of central WI may have this
precipitation fall as a rain/snow mix or even all snow. By Sunday,
the upper trough is projected to close off into an upper low over
the Midwest and the strong low pressure to move into eastern IA or
western IL. The warm front is forecast to push toward the WI/IL
border with the models showing a broad mid-level frontogenetical
signal over most of WI. Any snow or mixed precipitation will
quickly transition to all rain Sunday morning with rain likely
over all of northeast WI by Sunday afternoon. Combination of
clouds and precipitation will make it difficult for temperatures
to get out of the 40s on Sunday.

The system is progged to become vertically-stacked as it tracks
northeast into southwest WI Sunday night and northern sections of
the Great Lakes on Monday. Considering this system is stacked, the
GFS may be a bit hasty in pulling the system away on Monday and
prefer the slower movement like the ECMWF indicates. Assuming the
system follows this path, this would keep any convection and
heaviest rains to our east Sunday night, while the main
deformation zone with higher snow amounts would be to our
northwest. Nevertheless, we will still see some decent rain totals
over eastern WI with the potential for a light accumulation over
north-central WI later Sunday night into Monday morning. Too early
yet for specifics, so stay tuned to later forecasts! The chance
for rain would then continue for the rest of Monday as cold air
aloft wraps into WI behind the system and brings some instability
to the region.

Precipitation chances could even linger into Monday evening
(albeit very light) before finally tapering off later Monday
night. Big differences among the models with the handling of the
next system beginning next Tuesday. The ECMWF is much weak and
farther south than the GFS which is farther north and much wetter.
For now, will follow the consensus solution which favors the ECMWF
and keeps northeast WI dry on Tuesday.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1027 PM CDT Tue Apr 25 2017

A cold front will move slowly from northwest WI late this evening
to eastern WI Wednesday afternoon. A low pressure system will
lift northeast along this boundary, and produce periods of
showers, heavy at times. The rain should be focused over central,
north central and far northeast WI overnight, then overspread the
Fox Valley and lakeshore late tonight into Wednesday morning.
Additional showers and possibly a few thunderstorms may form along
the cold front over eastern WI Wednesday afternoon. However,
confidence is not high enough to include thunder in this set of
TAFs.

Expect flight conditions to deteriorate to MVFR as the heavier
rains develop, and to IFR on the cool side of the cold front. A
dry slot may bring a decrease in the rain over central and north
central WI Wednesday afternoon and evening, and allow for
improving visibilities.

Will keep LLWS in the MTW TAF, where it seemed most likely
overnight into early Wednesday.
&&

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

$$

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



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