Area Forecast Discussion
Issued by NWS Green Bay, WI

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014
FXUS63 KGRB 131749
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1249 PM CDT Fri Oct 13 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 309 AM CDT Fri Oct 13 2017

Low clouds and drizzle were noted across several locations early
this morning. The drizzle will linger through the morning hours,
eventually transitioning into light rain as a cold front tracks
through the area. The best chance for rain looks to be the
southern cwa where deeper moisture and strong 700 mb frontogenesis
will coincide during the afternoon hours. Under abundant cloud
cover, highs today are expected to range from around 60 across the
north, with lower to middle 60s across the south and east.

Rain chances will slowly fall during the overnight hours as the
front sinks south and stalls while lift decreases. Across the
north some clearing will allow lows to dip into the lower to
middle 30s, with lows around 50 across east-central Wisconsin
under mostly cloudy skies.

By Saturday the cold will lift back north as a warm front,
bringing increased chances for rain from south to north throughout
the daytime hours. The warm front will bring an influx of unstable
air into the region, bringing the possibility for a few elevated
thunderstorms Saturday afternoon across central and east-central
Wisconsin. The deep moisture and strong dynamics could bring
moderate to heavy rain at times during the afternoon hours. Highs
Saturday will range from the middle 50s across the north, with
lower 60s across the southeast.

.LONG TERM...Saturday Night Through Thursday
Issued at 309 AM CDT Fri Oct 13 2017

Once the initial upper trough exits into eastern Canada late this
weekend, the mean flow become progressive, nearly zonal across the
CONUS early next week. This is expected to change by the end of
the period as a new upper trough hits the western CONUS and
downstream building heights takes place over the eastern half of
the CONUS. The weather over northeast WI next week looks rather
docile with temperatures warming to above normal levels beginning
on Tuesday.

While the models agree that the area of low pressure will
intensify as it moves northeast into WI Saturday night, there is
still disagreement on the exact track. A more northern track (per
NAM/ECMWF) could place parts of the forecast area in the warm
sector and a better chance of seeing thunderstorms. A southern
track (per GFS/CMC) would keep the warm sector to our south and a
more limited storm threat. We will need to watch this situation
closely since 0-6km bulk shear values are very high and some of
these storms could get on the strong side with gusty winds. Other
aspects to watch out for will be increasing winds as the surface
low deepens and potential for heavy rain as PW values rise into
the 1.25-1.50 inch range. The heavier rain potential should taper
off after midnight as a dry slot rotates into the southeast half
of WI.

The windy conditions will continue through Sunday morning as the
strong low pressure races northeast into southeast Canada. We
could see sustained winds of 20 to 30 mph with gusts approaching
40 mph at times before winds gradually diminish in the afternoon
as a ridge of high pressure pushes into the Upper MS Valley.
Precipitation chances on Sunday look to mainly be confined to
northern WI as the trailing upper trough exits the area and the
onset of CAA could also add a bit of lake enhancement from Lake
Superior. Even with some afternoon sun mixed in with the clouds,
max temperatures will only be in the middle to upper 40s north-
central, lower to middle 50s east-central WI. Easily the coolest
day of the extended forecast.

A cold night is expected across northeast WI Sunday night as the
surface ridge axis slides across WI and winds diminish to around 5
mph (except 5-10 mph near Lake MI). Exactly show low temperatures
can get may depend on the amount of cloud cover as the models drop
a mid-level shortwave across WI primarily during the evening
hours. If the associated clouds can depart in time, central WI
would see their significant frost of the season. For now, have
temperatures in the lower 30s north-central, middle 30s central/
far northeast and upper 30s to around 40 degrees east-central WI.
As the surface ridge slides to our east, winds will back to the
west-southwest on Monday and allow for modest WAA to overspread
the region. Despite the warming aloft and a good deal of sunshine
expected, max temperatures will only be able to reach the lower to
middle 50s north, middle to upper 50s south.

A shortwave trough moving east across Ontario will help to pull a
cold front across WI Monday night. A lack of moisture would
preclude any precipitation, let alone have a hard time to generate
any clouds. On Tuesday, another ridge of high pressure is forecast
to move into the western Great Lakes, therefore bringing another
sunny day to northeast WI. Temperatures will slowly moderate with
readings on Tuesday around 60 degrees north/near Lake MI and
middle 60s south.

The moderation in temperatures will continue into midweek as the
pressure gradient tightens between the surface ridge now to our
east and strong low pressure moving across the Canadian prairie.
South winds of 10 to 20 mph by Wednesday would pull 8H
temperatures into the +10 to +14C range over northeast WI which
should bring max temperatures in to the lower to middle 60s north,
middle to upper 60s south.

Another very weak cold front is forecast to move into the western
Great Lakes region Wednesday night, but appears to dissipate as it
approaches the forecast area. Therefore, dry conditions to persist
right on through Thursday with the area remaining on the western
fringes of high pressure situated over the Mid-Atlantic states.
Temperatures to remain a good 10 degrees above normal.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1247 PM CDT Fri Oct 13 2017

The back edge of the low clouds will continue to make progress to
the southeast for a time this afternoon as a cold front crosses
the area. But the progress will likely slow later on as some light
rains moves through. A strong northward push of precipitation is
likely tommorrow as the primary cyclone begins to approach from
the southwest.
&&

.MARINE...
Issued at 309 AM CDT Fri Oct 13 2017

A strong low pressure system will move through the region this
weekend. Northeast winds will be veering from the northeast to
southeast through the day on Saturday with waves likely to exceed
small craft criteria (4 ft) on Lake Michigan. Then on the
backside of a surface low, winds will rapidly shift to the
northwest and become gusty on late Saturday night into Sunday. A
brief period of gale force gusts appears possible, particularly
during the late Saturday night into Sunday morning period.
Although headlines have not been issued, they are likely in
subsequent forecasts as the event draws closer.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......Skowronski
MARINE.........Kurimski



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