Area Forecast Discussion
Issued by NWS Green Bay, WI

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478
FXUS63 KGRB 151959
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
159 PM CST Wed Nov 15 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Thursday
Issued at 158 PM CST Wed Nov 15 2017

The latest RAP analysis and satellite/radar imagery show low
pressure centered over the eastern Upper Peninsula and a cold
front extending south from the low across eastern Wisconsin early
this afternoon. A secondary cold front is moving across northwest
Wisconsin. With help from a shortwave, an area of showers is
moving northeast across the Fox Valley, while spotty drizzle
persists over north-central WI under a low overcast deck.
Temperatures are slowly falling over north-central WI, though
remain in the middle to upper 30s. As temps fall into the lower
30s late this afternoon, some potential for drizzle to start
freezing on roadways over north-central WI. But with road temps at
or slightly above freezing, any freezing drizzle probably will be
spotty in nature. Forecast concerns revolve around light precip
across north-central WI tonight, and cloud trends.

Tonight...While most shower activity will be exiting eastern WI
by mid afternoon, light precip will be ongoing over north-central
WI at the start of the evening. Lake effect processes will slowly
ramp up through the evening as delta T`s fall into the mid teens.
But marginal instability and lack of deep saturation, to go along
with temps (and road temps) falling below freezing, will likely
call for a mix of snow and freezing drizzle from early to mid
evening until lake effect bands become better developed. Not out
of the question that slippery roads could develop. A period of
lake effect snow should then ensue from late evening into the
overnight. Lake effect parameters are not ideal despite decent
wind trajectories. Incoming mid-level dry air and marginal temps
should keep accumulations in check, and will continue to go with
an inch or two over northern Vilas county. For the rest of the
area, delayed the clearing trend until late tonight, and even then
it is questionable whether it will occur. Low temps ranging from
the mid 20s in the north to low 30s near the lake.

Thursday...Even though lake effect snow showers will mostly likely
have retreated into the Upper Peninsula by early morning, its
looking more likely that scattered to overcast skies will stick
around for much of the morning. Some clearing should take place
from late morning into the afternoon, but just when cirrus invades
from the west. High temps will range from near 30 in the north to
the upper 30s south.

.LONG TERM...Thursday Night Through Wednesday
Issued at 158 PM CST Wed Nov 15 2017

The main focus for the long term will be Thursday night through
Friday for the wintry mix across the region as the next system
passes through to start off the weekend.

The kitchen sink remains for Thursday night into Friday morning.
Recent models hold precipitation start off until around midnight,
with enough cold air and possible saturation to start off with
some light snow near Vilas County. The main challenge for this
part of the forecast will the be the warm air advection around
800-600 mb and the development of an associated dry slot. Current
depth of the dry layer is expected to be around 5000 feet which
should be just enough to prevent seeder feeder mechanisms and keep
freezing drizzle in the region for a portion of the morning in
the north. Slick spots could therefore affect the morning commute
on Friday as road temperatures ahead of the system remain well in
the 20s. By around noon to the afternoon, saturation of much of
the column will coincide with temperatures pushing into the
middle 30s throughout, bringing light rain showers to most of the
region into Friday evening.

The next hurdle for the forecast will arrive early on Saturday as
colder air follows behind the now retreating system. A switch back
towards more frozen precipitation can be expected, especially in
the northern portions of the forecast area. Models differ once
again in the speed at which this system retreats, but a switch
back to snow will be possible into Saturday afternoon. Can`t rule
out another brief chance of sleet or freezing drizzle before this
system is done. The remainder of Saturday will just see some
chances of lake enhanced precipitation lingering in the far north
towards Vilas County.

Dry and calmer conditions follow on Sunday and Monday. The next
system is shaping up to arrive Tuesday night to Wednesday with
another chance for some rain or snow.

Temperatures through the period will slip through the 30s Friday
and Saturday with highs in the 20s on Sunday before returning to
more seasonal conditions by next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1103 AM CST Wed Nov 15 2017

Spotty showers and drizzle will move across the region this
afternoon behind a cold front. Winds are slow to rise behind the
front, but think they will become gusty as colder air pushes into
the area this afternoon. Otherwise, the only significant change
was to delay upward trend of cigs until late tonight into Thursday
morning. Scattered snow showers remain on track to develop over
far north central Wisconsin this evening.
&&

.MARINE...
Issued at 158 PM CST Wed Nov 15 2017

Northwest winds behind a low pressure system remain on track to
strengthen and become gusty by early this evening. Winds have been
slow to ramp up this afternoon, and may struggle to reach 35 kt
gales until later in the evening. On the other hand, the latest
guidance suggest that the gale warning may need to be extended
into Thu morning, but will let evening shifts first see how winds
respond tonight.

Another low pressure system could bring additional chances for
gale force winds, first from the southwest on Friday ahead of the
system, then from the northwest behind the system on Saturday.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......MPC
MARINE.........MPC



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