Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 210331
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1031 PM CDT SAT AUG 20 2016

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 334 PM CDT Sat Aug 20 2016

Scattered showers continued to push across the area early this
afternoon as low pressure moved into far northeast WI and a
digging upper trough worked across MN. Dynamics, instability and
moisture were enough to produce at least 2 lines of showers with a
round of stronger convection during the late morning.

The final line of showers along the front will make its way across
eastern WI during the late afternoon hours, with more widespread
shower activity spreading into central and especially north
central WI closer to the upper trough, shortwave energy and
frontogenetic lift associated with the deepening low pressure. An
isolated rumble of thunder is possible, especially over eastern WI
where CAPE`s up to 600-1000 J/kg still exists, but no severe
weather is expected the rest of the day. Isolated heavy rain will
still be possible through the evening.

The low will deepen to around 990mb over eastern Lake Superior
this evening then continue to track NE into Canada. Gradient
tightens up as the low deepens, but the best gradient stays to
our north plus not the optimal time of day for mixing, so wind
gusts only around 20 mph are expected. Higher gusts are possible
over the water. See marine discussion for more info. Look for
showers to linger over northern WI much of tonight, with not much
activity for the rest of the area as best forcing stays closer to
the departing low and shortwave energy.

As the low continues to depart on Sunday, ridging builds into the
western Great Lakes through the day. However, a shortwave
tracking on the back side of the upper trough, along with
lingering moisture, could be enough to touch off a few showers or
sprinkles, especially in the morning. Cyclonic flow behind the low
will keep plenty of clouds in the area through Sunday morning,
with any areas of clearing filling in with daytime cumulus clouds.
Dry air will finally win out later in the day with some clearing
expected.

.LONG TERM...Sunday Night Through Saturday
Issued at 334 PM CDT Sat Aug 20 2016

Northwest upper flow will provide a break from the humidity
Sunday night through Monday night but warm and humid conditions
will return Tuesday and Wednesday as the flow becomes southwest.

A northward moving warm front may produce some thunderstorms
Tuesday night while a cold front brings another threat of storms
Wednesday afternoon and evening. A surface high should bring dry
weather Thursday through Saturday with near normal temperatures.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1024 PM CDT Sat Aug 20 2016

An upper level trough and secondary cold front will continue to
move through the region overnight, with most of the rain occurring
over north central WI. Showers have temporarily tapered off over
much of central and east central WI, and partial clearing has also
occurred. However, models suggest that clouds and scattered
showers will push back into this area when the secondary front
arrives later tonight. Much of the low clouds have eroded this
evening, but will not give up on the potential for widespread
MVFR and IFR flight conditions to redevelop overnight into early
Sunday morning. Rapid improvement should occur in the mid to late
morning, and partial clearing is anticipated as high pressure
arrives in the late afternoon and early evening.

Gusty west to northwest winds are possible at times tonight into
Sunday, but should decrease as the high arrives later Sunday
afternoon.
&&

.MARINE...

Close call on whether to go with a gale warning tonight as the
low pressure system deepens. NAM bufkit shows enough mixing to
bring down winds around 35 kts for a period tonight; however,
GFS/RAP show less mixing and no winds over 35 kts from the
surface to 10,000 ft. The warm waters of Green Bay and Lake
Michigan would favor enhanced mixing, along with a deepening low
pressure system and cold air advection on the back side. Best
pressure gradient seems to stay just to our north, so will hold
off a the gale warning and stick with a high end small craft
advisory with a few gale force gusts mentioned in it.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 11 PM CDT this evening FOR WIZ022-
040-050.
&&

$$

SHORT TERM.....Bersch
LONG TERM......RDM
AVIATION.......Kieckbusch
MARINE.........Bersch



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