Area Forecast Discussion
Issued by NWS Green Bay, WI

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643
FXUS63 KGRB 151714
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1114 AM CST Wed Nov 15 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 318 AM CST Wed Nov 15 2017

Light rain continues across north-central and northeast Wisconsin
ahead of an approaching cold front. However a swath of dry air is
inhibiting precipitation across much of central and east-central
Wisconsin. This dry air will limit how much rain falls across
these areas as the front moves through the area this morning. Rain
will come to an end as this first cold front passes through the
region.

A second cold front will move through during the afternoon hours,
causing temperatures during the afternoon to fall from west to
east after highs are realized during the morning or early
afternoon hours. The secondary cold front will cause gusty
northwest winds this afternoon, as winds become favorable for lake
effect snow to develop across north-central Wisconsin given the
fetch off Lake Superior.

The gusty winds will continue for much of the overnight hours as
lake effect snow accumulates across north-central Wisconsin.
Snowfall accumulations are expected to be light, mainly a dusting
with 1 to 2 inches possible across Vilas County.

High pressure will build in on Thursday, ending the lake effect
snow across north-central Wisconsin as winds die off and skies
become mostly sunny.

.LONG TERM...Thursday Night Through Tuesday
Issued at 318 AM CST Wed Nov 15 2017

Main focus will be the light wintry mix late Thursday night into
Friday morning, and then potential for the rain to change back
to snow late Friday night into Saturday morning north and west
of the Fox Valley. Blustery and colder conditions expected
over the weekend.

For Thursday night into Friday morning, threw in the kitchen sink
with respect to precipitation types. Models indicated low clouds
developing below an inversion, especially north and west of the
Fox Valley late Thursday night. Enough dry air between 850mb to
700mb to negate the seeder feeder mechanism, thus current belief
is that precipitation will start out in the form of freezing
drizzle. Road temperatures north and west of the Fox Valley
should be in the 20s to around 30, thus slick spots are expected
if the freezing drizzle develops as expected. Late Thursday
night (towards 12z on Friday), the model indicated the wedge
of dry between 850mb and 700mb erodes, thus could not rule out
snow flakes. Meanwhile, strong southerly winds are ushering much
warmer air with the 850mb 0C isotherm line pushing into northern
Wisconsin. It appears that any snow amounts would be minor at
best. As the warm air pushes northward between 6 am and 10 am, the
moisture increase through much of the column, thus the freezing
drizzle is expected to change over to brief period of freezing
rain. Also, the models are now suggesting a cold pocket around 925
mb where the liquid precipitation may refreeze as sleet. Think
there will be a period between 6 am and 10 am of sleet and
freezing rain before changing to rain by late morning. The 10 am
time frame is assuming air/road temperatures climb well above
freezing. Based on past experience, road temperatures by late
morning across the north should be in the middle 30s. Light rain
and drizzle will continue Friday afternoon into Friday evening.
Gusty southerly winds are expected Friday afternoon with gusts
over 30 mph possible across eastern Wisconsin.

For Friday night, the precipitation should be in the form of
light rain or drizzle across much of the area. As the colder air
filters in across the far north, the precipitation is expected to
change back to snow. Could not rule out a brief period of light
freezing rain or sleet as well, but did not include this in the
forecast at the moment. The main change to this period was to slow
down the cooling and change over of the precipitation across the
north. An upper level disturbance will bring a chance of rain/snow
showers into Saturday night. The snow showers will linger across
the far north into Sunday morning until the low level winds back
to the west.

Tranquil conditions expected Sunday night into Monday night.
Next system brings a chance of rain or snow to northern
Wisconsin on Tuesday. Temperatures in the upper 30s to
middle 40s Friday, cooling into the upper 20s to middle
30s by Sunday. Temperatures return to or slightly
above seasonal normals early 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 318 AM CST Wed Nov 15 2017

A low pressure system tracking through the western Great Lakes
will cause a tight pressure gradient across the region through
Thursday. Strong southerly winds will cause waves to pile up along
the nearshore waters of Lake Michigan and central Bay of Green Bay
with gusty westerly winds behind the passage of a cold front later
today. Given the high winds and waves a Small Craft Advisory is in
effect for all zones today.

A secondary cold front will bring very gusty northwest winds
tonight with Gale force winds expected around the Door Peninsula
north of Sturgeon Bay. With stronger winds than previously
expected will issue a Gale Warning for these areas tonight.
Further south a few Gale force gusts are possible, however they
are not expected to be persistent enough to upgrade from the Small
Craft Advisory currently in effect.

High pressure will build in across the western Great Lakes on
Thursday causing winds and waves to subside below criteria by the
early afternoon hours.

Southerly Gale force wind gusts are possible Friday over the Lake
Michigan nearshore waters as a low pressure system approaches
from the west. After this system tracks through Friday night,
northwest Gale force wind gusts are possible on Saturday for the
areas surrounding northern Door County.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......MPC
MARINE.........Kurimski



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