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910
FXUS63 KGRB 271740
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1240 PM CDT Tue Jun 27 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 257 AM CDT Tue Jun 27 2017

High pressure will track through the western Great Lakes region
today, bringing mostly sunny skies and warmer high temperatures
during the afternoon hours. Highs will still be below normal for
this time of year, however the area is expected to at least get
into the lower to middle 70s.

A low pressure system will approach the upper Mississippi Valley
on Wednesday, bringing rain to the western Great Lakes throughout
the day. Recent model runs indicate the rain should hold off until
Wednesday, therefore will dry out the forecast for the area during
the overnight hours. POPs for Wednesday will be fairly high given
a vigorous mid level PV anomaly and abundant isentropic lift
across the western Great Lakes region. Moisture will be plentiful
as PWATs approach 2 inches during the afternoon hours, bringing
the threat for heavy rain at times.

Instability will also introduce a risk for severe weather as
MUCAPEs rise to 500 to 1000 J/kg, especially across central
Wisconsin. Despite the instability and lift, the best chance for
severe weather appears to be to the southwest given much better
instability. However there still exists a marginal risk for severe
weather across the area, mainly along and south of highway 29
during the afternoon hours.

.LONG TERM...Wednesday Night Through Monday
Issued at 257 AM CDT Tue Jun 27 2017

A brief period of zonal flow is expected at the beginning of the
period. A 500mb trough will swing across the region late in the
work week into the weekend followed by a northwest flow aloft
late this weekend into early next week. This pattern will lead
to periodic chances of showers and thunderstorms late Thursday
night through the weekend and into early next week.

For Wednesday night, thunderstorms will be ending from west to east
as a cold front moves across the region. A few storms could be on
the strong to severe side across central into northeast Wisconsin
with damaging winds and large hail. A few showers will linger
across the region overnight, and across the far north into early
Thursday morning. The next system approaches from the west late
Thursday night into Friday morning. Still some uncertainty in the
track of the system which will impact rain chances. during this
period.

Upper trough swings across the region Saturday into Monday, bringing
chances of showers and thunderstorms. The best chance for thunderstorms
will be during the afternoon and early evening hours each day. It is
too early to determine if any of the storms would become severe. No
real significant chances to max/min temperatures during the period.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1239 PM CDT Tue Jun 27 2017

Expect mainly dry and VFR conditions the rest of today and 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. There is a chance
for thunderstorms starting Wednesday morning and flying conditions
look less and less promising as we get later in the day. Along
with abundant rainfall, there should be plenty of MVFR ceilings,
with scattered IFR, by midday. Some of the stronger thunderstorms
could produce large hail and wind gusts in excess of 50 kts.
&&

.MARINE...
Issued at 257 AM CDT Tue Jun 27 2017

A low pressure system approaching the western Great Lakes region
will cause southerly winds to increase across the nearshore waters
Wednesday and Wednesday night. This will cause winds to increase
to 25 to 30 knots, with a few gusts approaching gale force at
times, especially across the Lake Michigan nearshore waters. Waves
will also increase during this period, with the highest waves
across the Lake Michigan nearshore waters. Although headlines have
not yet been issued, they are likely in future issuances. Any
boaters planning on traveling on Wednesday and Wednesday night
should follow future forecasts closely.
&&

.HYDROLOGY...
Issued at 257 AM CDT Tue Jun 27 2017

A developing low pressure system tracking northward over Minnesota
Wednesday into Thursday, lifting a warm front northward across
the Western Great Lakes region. South winds will return a more
moist air mass into the region with showers and storms along and
near the front. 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 of locally heavier
rainfall will likely be associated with any training thunderstorms
along the warm front. This could exacerbate rivers that are
already above bankfull and bring the threat for flooding across
area rivers.
&&

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

$$

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