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Area forecast discussion
National Weather Service Green Bay WI
1133 am CDT sun Oct 20 2019

Updated aviation portion for 18z taf issuance

Short term...today...tonight...and Monday
issued at 340 am CDT sun Oct 20 2019

Morning fog will persist several hours after sunrise with an
expansive stratus deck in place. The fog should dissipate by 9 or
10 am. A fairly calm and quiet day will be had across the western
Great Lakes today as temperatures rise into the upper 50s to lower
60s with just a few high clouds to contend with one the morning
fog dissipates.

A low pressure system developing across the Central Plains will
track towards southwest Minnesota late tonight, then continue
east-northeast through northern Wisconsin on Monday. Rain chances
will steadily increase late tonight into Monday as the low
approaches the region. However the latest model runs are a bit
slower with the onset of precipitation, holding if off until after
midnight. Once the main low gets closer the system will have
abundant lift and moisture to work with as pwats approach 1 inch,
which is around the 90th percentile for this time of year. The
system will also have quite a bit of isentropic lift and dynamics
from a mid level shortwave and the left exit region of a strong
140 knot upper level jet. There will be a chance for thunder with
a few hundred j/kg of MUCAPE which could create heavy downpours at
times. Given the amount of moisture and lift from this system
there is the potential for an inch or two of rain on Monday,
however it has been several weeks since a significant widespread
rainfall so while localized flooding is possible, it is not
expected to be widespread or high impact.

Monday is also expected to be fairly windy as the pressure
gradient tightens ahead of the approaching low with the highest
winds across east-central Wisconsin and the Lakeshore given the
onshore southeasterly component to the winds. The persistent gusty
southeast winds along with high waves of 6 to 10 feet and high
water levels of Lake Michigan could cause some Lakeshore flooding
issues across door, Kewaunee, and Manitowoc counties on Monday.
These conditions may warrant Lakeshore flood headlines in
subsequent forecasts.

Long term...Monday night through Saturday
issued at 340 am CDT sun Oct 20 2019

A strong surface low pressure system and a closed upper level
cyclone will bring rain and much colder temperatures to the area
as these features move across northwest Wisconsin and continue to
Ontario Monday night and Tuesday.

There is a chance for showers on Monday night but rain chances are
highest on Tuesday. Precipitation chances are mainly confined to
north-central Wisconsin on Tuesday evening when there will be
enough cold air to change rain showers to a mix of rain and snow.
There will only be a slight chance for rain and/or snow in the
north later Tuesday night as the surface and upper systems
continue to move away from Wisconsin.

A passing upper level short wave and surface trough/cold front
will increase the chance for precipitation Wednesday afternoon
into Thursday morning. Any precipitation that does fall should be
in the form of rain Wednesday, but a change to a mix or snow can
be expected in the north and parts of central Wisconsin Wednesday
night, before a change back to just rain occurs as the boundary
layer warms up during day on Thursday.

The rest of the week into next weekend appears mainly dry with a
surface ridge passing through Wisconsin. There may still be a
slight chance for rain and/or snow at times since an upper trough
will be moving through the region at the same time.
&&

Aviation...for 18z taf issuance
issued at 1132 am CDT sun Oct 20 2019

Low stratus continues to rapidly dissipate late this morning,
which should leave mostly clear skies for the rest of the
afternoon.

An approaching low pressure system remains expected to bring in
clouds above 15 kft this evening, before low clouds arrive late
tonight. Low level wind shear is also forecast to develop late
tonight as well, which will persist through much of Monday
morning.

Light to moderate rain showers are anticipated to move from
southwest to northeast across the region on Monday morning. A few
thunderstorms are possible, mainly from late morning into the
afternoon. The showers could bring down some brief gusty winds
above what is explicitly stated in the tafs.

&&

Marine...
issued at 340 am CDT sun Oct 20 2019

A tight pressure gradient ahead of an approaching low will cause
southeast winds to gust to around gale force across the Lake
Michigan nearshore waters on Monday. The low will then stall
across the northwest Great Lakes region, with continued
southwest gales Monday night and Tuesday. The low will then
slowly lift north Tuesday night with gale force winds coming to an
end late Tuesday night as the pressure gradient eases across the
western Great Lakes region. Given the long period of gale force
winds will issue a gale watch for the Lake Michigan nearshore
waters from Monday morning through Tuesday night.

Across the Bay of Green Bay winds are expected to gust to around
30 knots, with gale force winds possible at times. However given
the Bay is more sheltered from southeast winds on Monday will not
extend the gale watch into this area, but a Small Craft Advisory
is likely in future forecasts. Gale force winds are possible on
the Bay Monday night and Tuesday with funneling from southwest
flow, but will hold off on these headlines until future forecasts
as the wind gusts are less certain across the Bay for this period.
&&

Grb watches/warnings/advisories...
none.
&&

$$

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