Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 292004
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
304 PM CDT Sat Apr 29 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 304 PM CDT Sat Apr 29 2017

Precipitation timing and amounts are the main concerns during
this part of the forecast.

Surface low pressure and a 500mb low over the Plains will approach
the western Great Lakes, bringing rain to central and northern
Wisconsin tonight and Sunday.

A radar loop of the region at 1915Z showed rain pushing northward
but making little progress into Wisconsin. The rain will take a
little while to reach the forecast area due to the dry air in
place. This evident on the 12Z GRB sounding, where PWAT was only
0.27 inch, and surface observations, where temperatures were
mainly in the mid 40s to around 50 degrees and dew points were
generally in the 20s.

12Z models showed some differences in timing but generally agree
on rain reaching the southern part of the forecast area during the
evening and continuing to push northward overnight. The far north
looks to remain dry through the night, before the rain reaches
that part of the state on Sunday as the system gets closer to
Wisconsin. There could be some snow or mixed rain and snow across
parts of central Wisconsin tonight, but no accumulation is
expected.

Showers should continue across the entire area on Sunday, and
some of the models indicated elevated CAPE across the southern
part of the forecast area. Have a mention of thunder in parts of
central and east central wisconsin as a result of this elevated
instability.

The ECMWF and Canadian both had much higher QPF across parts of
east central Wisconsin than the NAM or GFS. WPC had the far
southeast corner of Manitowoc County in a marginal risk of
rainfall exceeding flash flood guidance through 12Z Sunday. Will
have to keep an extra close watch on rainfall totals across east
central Wisconsin overnight for this reason.

Made few changes to overnight lows and highs for Sunday.

.LONG TERM...Sunday Night Through Saturday
Issued at 304 PM CDT Sat Apr 29 2017

A slow moving low pressure system will track through the western
Great Lakes region late Sunday night through Monday night. Overall
the models seem to have a good handle on the system, with a dry
slot late Sunday night and Monday morning, possibly offering a
brief respite in rain chances before wrap around moisture brings
another round of rain Monday afternoon and Monday evening before
rain chances drop off later Monday night and Tuesday as the main
low pulls away from the region. Abundant lift and moisture from
this system will bring a swath of moderate to heavy rain at times,
exacerbating the flooding concerns on area rivers. Although a
flood watch in the future is certainly possible, there is still
enough spread in the model qpf amounts to hold off at this time.

As the system pulls away Monday night and Tuesday cold air
filtering in behind the system may mix in some snow across the
north. However given the wet ground from the recent rains not much
in the way of accumulation is anticipated.

A stretch of quiet weather is on tap during the middle part of the
week as high pressure makes its way through the western Great
Lakes region. A weak low pressure system will track through the
area late in the week, bringing a chance for rain showers Thursday
and Thursday night. This system will lack strong dynamics and
lift, so even if rain falls it will be on the light side. High
pressure will then build back into the area, keeping the weather
dry for Friday and next Saturday. Overall models are in fairly
good agreement for the far extended.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1235 PM CDT Sat Apr 29 2017

Generally VFR conditions can be expected into the evening hours
before ceilings and visibilities gradually become MVFR from
southeast to northwest. IFR ceilings should develop in east
central Wisconsin later in the night as a surface low moves from
the Panhandle region to the central Plains. Expect MVFR and IFR
conditions to prevail through at least Sunday morning with the
approach of the low. The exception is the northern part of the
forecast area which remain VFR overnight with MVFR conditions
developing Sunday morning.
&&

.MARINE...
Issued at 304 PM CDT Sat Apr 29 2017

Increasing northeast winds along Lake Michigan will likely
produce high waves this weekend into early next week. Winds may
approach gale levels late this weekend into early next week ahead
of a strong system as it tracks into the Great Lakes region.
&&

.HYDROLOGY...
Issued at 304 PM CDT Sat Apr 29 2017

Above normal rainfall for April continues to keep river levels
and flows above normal. Recent rainfall from earlier this week
have prompted river flood warnings for part of the Wolf river
south of Shawano. Flows along the Menominee also remain above
normal, with flood advisories in effect for portions of the river
and possible flood warnings for minor flood stage this weekend.
Another storm system Sunday into Monday will be capable of
producing another widespread 1 to 2 inches of rainfall over two
days with locally higher amounts possible. This rainfall will
continue to keep river running above normal into early May. The
above normal river levels and flows will likely begin to affect
recreational users and interests. Be current with any slow no wake
postings in your area.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Kurimski
AVIATION.......MG
MARINE.........Kurimski
HYDROLOGY......Kurimski


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