Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 262337
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
637 PM CDT Fri May 26 2017

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 251 PM CDT Fri May 26 2017

Scattered showers and gradually turning cooler during the holiday
weekend.

Northwest upper flow will develop across the region as a ridge
sets up over western North America and an upper trough settles in
over Ontario. The pattern does not appear as though it will be
exceptionally long-lived, as deamplification is likely to begin by
late in the period.

Temperatures will start the period near seasonal normals, then
drop back to a little below normal in the developing northwest
flow. There will be several opportunities for precipitation, but
most precipitation events look to be composed of scattered to
numerous showers so amounts are likely to end up near normal for
the 7 day period.
&&

.SHORT TERM...Tonight and Saturday
Issued at 251 PM CDT Fri May 26 2017

Precipitation chances remain somewhat uncertain due to weak
forcing. Trended PoPs upward this evening and then down after
midnight, following the most recent HRRR runs. Remnants of a weak
boundary will linger across the area Saturday, again leading to
rather nebulous forcing. Stuck with mainly chance PoPs with the
best chance in the afternoon.

Dense fog over Lake Michigan has primarily remained offshore, but
southeast low-level flow could bring it inland. The main concern
is highways near the lake which are likely to have a high traffic
volume at the start of the holiday weekend. Plan to handle the
situation with SPSs unless fog makes a more aggressive surge
inland. Winds may turn offshore later tonight and push the fog
farther out into the lake, but again models differed in the
details of that in the weak low-level pattern.

.LONG TERM...Saturday Night Through Friday
Issued at 251 PM CDT Fri May 26 2017

Northwest flow aloft will continue through much of next week as
500mb ridge remains entrenched across western North America with a
downstream trough across eastern North America. Upper level
disturbances and associated weak cold fronts will bring periodic
chances of showers and a few thunderstorms from time to time
through much of the period.

For Saturday night, weak frontal boundary across the area,
combined with daytime heating will allow for scattered shower to
linger into the evening hours. A thunderstorm could not be ruled
out. After midnight, two systems will approach the area. The first
system will pass to the south of the area while the second system
will approach from the northwest. These two systems will bring
increasing chances of showers overnight into Sunday morning. The
next weak cold front will move across the area Sunday afternoon.
This feature will bring continued chances of showers with a few
thunderstorms expected. Most of the shower activity will end
during the evening hours. With northwest flow aloft, could not
rule out an isolated shower after midnight.

Next shortwave energy and upper trough swing across the area
on Memorial Day. With daytime heating, instability showers will
be on the increase during the late morning and afternoon. A few
thunderstorms are possible. Due to expected cloud cover and rain,
lowered high temperatures on Memorial Day. Also, gusty westerly
winds are expected with gusts around 30 mph possible.

More instability showers are expected Tuesday, and again Wednesday
and Thursday. Most of the time will be dry, however the best
chances of rain appear to be during the afternoon hours.
Temperatures during the period will be at or slightly below
average.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 629 PM CDT Fri May 26 2017

Scattered showers should edge out of northern WI later tonight,
and the scattered line of thunderstorms over the northwest part
of the state should dissipate as daytime instability wanes.
Partial clearing, light surface winds, boundary layer winds of
15 knots or less and low-level moisture will likely lead to areas
of fog and low clouds late tonight, with localized LIFR/VLIFR
flight conditions possible. Dense fog is also possible along the
lakeshore, but whether or not this will reach the MTW TAF site is
uncertain. The fog should mix out early Saturday morning. Daytime
heating and the presence of a weak boundary in eastern WI may
result in scattered showers and isolated thunderstorms late in the
afternoon. Will mention VCSH at GRB/ATW, but confidence is not
high enough to mention thunderstorms at this time.

&&

.MARINE...
Issued at 251 PM CDT Fri May 26 2017

Dense fog will continue tonight into Saturday on Lake Michigan.
Patchy dense fog is also possible on the Bay of Green Bay. The
fog may linger into Saturday night on Lake Michigan. There is
a slight chance of thunderstorms during the afternoon and
early evening hours Saturday, Sunday and Memorial Day that may
pose a hazard to mariners.

Gusty westerly winds are expected on Memorial Day with gusts
around 25 knots possible making for hazardous conditions for
small craft.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......Kieckbusch
MARINE.........Eckberg


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