Small Craft Advisory 74, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
647 PM CDT Sun Oct 4 2020

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 242 PM CDT Sun Oct 4 2020

The latest RAP analysis and satellite/radar imagery show surface
high pressure stretching from western Lake Superior to the
southern Plains early this afternoon. Diurnally enhanced
convective clouds are holding tough over northern WI thanks to
moisture fluxes off Lake Superior and northern Lake Michigan.
Clouds further south over central and east-central WI have been
eroding, except near the Lake Michigan shoreline. With further
mixing into dry air, should see the clouds dissipate by late
afternoon. Looking upstream, mostly clear skies are present near
and west of the surface high. As this high moves across the region
tonight and west of the region on Monday, forecast concerns
mainly revolve around frost potential and gusty south winds.

Tonight...High pressure will slide across the region during the
evening to the central Great Lakes overnight. Most of the evening
will see clear skies and light winds, which will promote tumbling
temperatures. Some mid and high clouds do invade far northern WI
overnight, while boundary layer winds start to increase over
central and north-central WI. But conditions should be supportive
for a long enough time to generate frost over much of the region. With
agricultural interests determining that the growing season has
ended over central WI, will issue a frost advisory for parts of far
northeast and east-central WI, excluding Door County. Lows will
generally range from upper 20s to mid 30s away from the Lake.

Monday...Southwest winds will be strengthening ahead of a weak
cold front moving across the northern Mississippi Valley. Strong
gusty winds to 35 mph can be expected, peaking late in the
afternoon. Otherwise, should see ample sunshine, with only some
scattered mid and high clouds overhead at times. The southwest
winds will usher in warmer air, with highs ranging from the mid
50s to lower 60s, which is near normal for the date.

.LONG TERM...Monday Night Through Sunday
Issued at 242 PM CDT Sun Oct 4 2020

An upper trough and Pacific cold front could produce a few sprinkles
or very light showers as it moves across the area Monday night.
Clouds and a steady breeze will hold temperatures up Monday night.

After a breezy and milder day Tuesday, a more vigorous upper trough
and accompanying weak cold front has a little better chance of
producing showers across northern Wisconsin Tuesday night, but the
best dynamics are across Upper Michigan. Highs will be about five
degrees above normal.

Dry and mild weather is expected Wednesday through Saturday. There
is a small chance that some showers could accompany a warm front
moving north across the region Friday, but not sure at this point.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 637 PM CDT Sun Oct 4 2020

Wind/LLWS will be the main concerns during this TAF period.

Diurnal cumulus/stratocumulus have eroded rapidly early this
evening, leaving clear to partly cloudy skies. Winds were light
and variable due to a surface ridge of high pressure residing over
the forecast area.

The surface ridge will shift east overnight, allowing south to
southwest winds to develop. The winds aloft will increase first,
resulting in LLWS at the RHI/AUW/CWA TAF sites late tonight into
Monday morning. By 15z-16z/Monday, surface winds will increase
significantly, with gusts to near 30 knots expected through the
afternoon. As the surface winds decrease Monday evening, LLWS
will ramp up again.

VFR conditions will prevail through the entire TAF period.

&&

.MARINE...
Issued at 242 PM CDT Sun Oct 4 2020

Gusty northerly winds will cause conditions hazardous to small
craft through the end of the afternoon. Buoys over the northern
Lake have been consistently running in the 4-6 ft range so far
today, though those higher waves are most likely further out
towards the open waters and not right up against the shoreline.

The area will be in between a departing high to the southeast and
an approaching low pressure system to the northwest Monday and
Monday night. This will bring gusty south winds to the Lake
Michigan waters Monday afternoon and Monday night. Winds could
gust to gale force at times, especially around the Door Peninsula
late Monday afternoon and evening. Gale headlines may be needed
in subsequent forecasts if these wind gusts maintain themselves or
increase. Winds do not look quite as strong on the Bay, but may
approach gale force for a few hours late in the afternoon into
early evening as well.

Will let the current small craft advisory expire before issuing
headlines for Monday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 11 PM this evening to 8 AM CDT Monday for
WIZ020-031-037>040-045-048>050-073-074.
&&

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

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