Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 272328
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
628 PM CDT Tue Jun 27 2017

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 258 PM CDT Tue Jun 27 2017

Showers and thunderstorms are expected Wednesday and Wednesday
evening, with heavy rainfall possible.

The large scale pattern across North America will briefly
deamplify the next couple days, as the upper trough currently over
the Great Lakes region reforms back over the Rockies. The pattern
will become slowly progressive and gradually reamplify, with the
new trough passing through the Great Lakes region during the
upcoming weekend. By Independence Day, the trough should be over
eastern North America with another trough back near the West
Coast, and broad ridging in between.

The large scale pattern should result in temperatures fairly
close to seasonal normals, though with day to day variations due
to precipitation and differences in cloud cover. The westerlies
will remain fairly energetic for late June, so precipitation
amounts will probably end up above normal for the period.
&&

.SHORT TERM...Tonight and Wednesday
Issued at 258 PM CDT Tue Jun 27 2017

Surface high pressure over Illinois today, along with an upstream
mid level ridge will keep the forecast area mostly dry through 12Z
Wednesday. Ongoing thunderstorms are expected to move into
central/north central Wisconsin around 12Z in warm advection
ahead of an approaching mid level short wave. Advection of warm
and moist air ahead of the system is forecast to have PWATS of
1.5 inches or more across the area. Models were all showing
significant amounts of QPF in central and/or northern Wisconsin
during the day on Wednesday.

SPC day 2 convective outlook had much of the area in a marginal
severe risk and parts of central Wisconsin in a slight risk of
severe. The risk of severe storms looks to be higher to the
southwest where MUCAPE and shear values are higher, but MUCAPES
are still expected to be 500+ J/kg over most of the area.

Have cooler high temperatures for Wednesday due to abundant
cloud-cover and rainfall.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 258 PM CDT Tue Jun 27 2017

The coverage and intensity of convection Wednesday evening will
depend on earlier-day storms. Opted to keep likely PoPs going
into the evening, with a sharp downward trend after midnight.

Other than some low PoPs across the far north, the blended
guidance continued to have a dry forecast for Thursday. As
mentioned yesterday, with a relatively weak surface pressure
pattern across the area and lingering moisture from the rains
expected Wednesday and Wednesday night, it`s hard to rule out the
development of some showers/thunderstorms during peak heating.
But will stick with the dry forecast for now and take another
look tomorrow.

The next substantial chance for rain will probably arrive either
late Thursday night or Friday morning, as a wave develops and
rides northeast along the front stalled to our south. Models
differ on the specifics, though most suggest just light-moderate
amounts, centered over east-central Wisconsin. Of most concern is
the ECMWF which showed much heavier precipitation in east-
central Wisconsin. Will stick with the more modest PoPs and QPF of
the model blend for now with the idea the prior convection could
shove the front even a little farther south than currently
forecast.

Precipitation chances during the weekend will depend on small
shortwaves rotating through the large scale trough crossing the
region. There should be a diurnal component as well, with mid-
afternoon to early evening being the most favored time for
precipitation. The forecast for Monday is dry, though any slowing
of the eastward progression of the large scale trough could result
in some light precipitation Monday afternoon as well. The Fourth
of July looks dry at this point, with highs near or a little above
seasonal normals.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 626 PM CDT Tue Jun 27 2017

Expect mainly dry and VFR conditions most of the night as surface
high pressure drifts to the east and a mid level ridge moves to
central Wisconsin by 12Z Wednesday. Increasing southerly winds
aloft will bring LLWS to central and north central Wisconsin
starting late tonight. Scattered showers and storms expected
starting Wednesday morning with lowering cigs and vsby. Scattered
IFR by midday.

&&

.MARINE...
Issued at 258 PM CDT Tue Jun 27 2017

Southerly winds will increase across the nearshore waters
Wednesday and Wednesday night. This will cause winds to increase
into the 25 to 30 knot range, with a few gusts around gale force
at times, especially across the Lake Michigan nearshore waters.
Waves will increase with the increasing winds, with the highest
waves across the Lake Michigan nearshore waters. Planning to go
with a high end small craft advisory at this point. Any boaters
planning on traveling on Wednesday and Wednesday night should
follow future forecasts closely.
&&

.HYDROLOGY...
Issued at 258 PM CDT Tue Jun 27 2017

Periods of heavy rainfall are likely with a widespread 1 to 2
inches across much of the state Wednesday and Wednesday night. The
greatest potential for locally heavier rainfall will likely be
with any training thunderstorms along the warm front. This could
cause rivers, that are already above bankfull, to rise and bring
the threat for flooding.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from Wednesday morning through Thursday
morning for WIZ022-040-050.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....MG
LONG TERM......Skowronski
AVIATION.......JKL
MARINE.........MG
HYDROLOGY......MG



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