912
FXUS63 KGRB 222314
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
614 PM CDT Sun Sep 22 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Gusty north winds and building waves into Monday morning will
  result in hazardous conditions for small craft. Dangerous
  swimming conditions are also expected at Lake Michigan beaches,
  mainly south of Sturgeon Bay. A Small Craft Advisory and Beach
  Hazard Statement remains in effect.

- Patchy to areas of frost are expected to develop across north-
  central WI early Monday morning and possibly again on Tuesday
  morning. A Frost Advisory has been issued for portions of
  northern Wisconsin tonight.

- Temperatures closer to normal are expected through the middle of
  the week before trending well above normal late this week,
  where high temperatures could run as much as 10 to 15 degrees
  above normal.

&&

.DISCUSSION...
Issued at 354 PM CDT Sun Sep 22 2024

Short Term...Tonight and Monday

Main forecast concerns in the short-term are cloud trends through
this evening and frost potential overnight.

This afternoon`s satellite and radar imagery indicated the cold
front that moved through the forecast area earlier today was located
in southeastern WI/northeastern IL. In the wake of this front,
clouds were slowly departing the forecast area to the southeast with
light drizzle observed in east-central WI. Otherwise, skies were
mostly sunny in central WI and across the Northwoods. CAA in this
area also aided in breezy northerly winds to mix to the surface this
afternoon, with gusts up to 25 mph.

This evening and tonight...As dry air continues to filter into the
area with the arrival of a high pressure system, clouds will clear
and winds will become calm. Much cooler air will also spread over
the area with lows ranging from the low to middle 30s in north-
central WI to the low to middle 40s elsewhere. Given the clear
skies, light winds, colder temps, and a low-level temperature
inversion, anticipate frost to develop across north-central WI.
Decided to issue a Frost Advisory for locations in north-central WI
given the favorable elements and probabilities for temperatures less
than 37 degrees increased from the previous forecast from up to 50%
to up to 75%. Patchy fog may also develop in these areas given it
will be a decent radiative cooling night. The Frost Advisory is in
effect from 2am to 8am Monday.

Monday...Any frost development will end and any fog will burn off as
the sun rises. With the high pressure overhead, dry and mostly sunny
conditions with light winds are expected for the rest of Monday. The
cooler air mass sticks around for Monday, but highs will be near
normal with values ranging from the middle 60s to low 70s.

Long Term...Monday Night Through Sunday

Chilly again on Monday night over the north. Min temps in the
middle 30s at typical cold spots. Similar to tonight with light
winds and mostly clear skies, could see patchy fog and patchy
frost.

Only chance of rain for the workweek is on Tuesday as H5 trough
shifts across the central Great Lakes. Appears areas from Fox
Valley east to the lakeshore and to Door County could see some
light showers (chances around 20%) though most rain stays over
central Great Lakes. Signal that once that system shifts east
Tuesday night, lingering dry air and light winds may lead to
another chilly night over northern WI with potential for fog
and frost.

Rest of the week looks quiet as ridging sfc and aloft builds
across the western Great Lakes. Given warming H85 temps and plenty
of sunshine expected, high temps may make another run at 80
Thursday and/or Friday. Easterly low-level winds will keep temps
cooler near Lake Michigan. By late week, attention will likely be
on the Gulf Coast as another tropical system may be impacting that
part of the county. What becomes of that system (how far northwest
will it drift and how strong will it be by that time) dictate
whether any chances of rain materialize here next weekend. Model
spread is all over the place though and run-to-run model consistency
is poor as well. Will not make many changes to blended grids at
this point which feature broadbrushed low-end chances Saturday and
Sunday. Highs next weekend will remain at least in the lower 70s,
which remains above normal (normal highs for the last full weekend
of September are in the low to mid 60s).

Beyond the forecast period, the 8-14 day outlook from the Climate
Prediction Center is calling for a greater chance of above normal
temperatures and a greater chance of below normal precipitation
and looking even farther ahead into mid October, the experimental
week 3-4 outlook from CPC indicates there really is no change in
this overall pattern. Guess that makes sense as looking at past
La Nina winters, which is expected this winter, there was a strong
signal for the fall to be warmer than normal at Green Bay.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 613 PM CDT Sun Sep 22 2024

Skies were clearing from west to east early this evening as all
TAF sites had lifted to VFR. Skies will continue to clear this
evening as high pressure builds in across the western Great Lakes.
Mostly clear skies are then expected during the overnight hours.
Some patchy ground fog may develop across north-central Wisconsin
late tonight into early Monday morning, which may lower conditions
to MVFR/IFR at times. Any fog will lift Monday morning, with
mostly sunny skies and VFR conditions expected Monday.

Gusty northerly winds to 20 knots early this evening will ease
and become light overnight into Monday.

&&

.MARINE...
Issued at 354 PM CDT Sun Sep 22 2024

Gusty northerly winds developed behind a cold front this
afternoon, leading to hazardous conditions for small craft.
Anticipate the northerly winds, with gusts of 25-30 kts, to
continue through at least late tonight. The gusts may continue
into Monday morning, however, there is some uncertainty of how
long the gusty winds will prevail. In addition to the winds,
waves up to 3 ft are expected on the bay and up to 6 ft on Lake
Michigan, highest south of Sturgeon Bay. For now, kept the same
timing of the Small Craft Advisory, which expires Monday morning,
but could see it expiring early.

Although winds will mainly be out of the north, there will be
just enough of an easterly component to bring 3+ waves to the
shores of Lake Michigan beaches. This will create dangerous
swimming conditions, mainly south of Sturgeon Bay. A Beach Hazards
Statement remains in effect.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 8 AM CDT Monday for WIZ005-010>012-
018-019.

Beach Hazards Statement through Monday morning for WIZ022.

Beach Hazards Statement through Monday afternoon for WIZ040-050.
&&

$$

DISCUSSION.....Kruk/JLA
AVIATION.......Kurimski
MARINE.........Kruk