813
FXUS63 KGRB 181140
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
640 AM CDT Fri Oct 18 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Elevated wildfire conditions possible today central to north-
  central Wisconsin due to gusty winds, low humidity, above normal
  temperatures, and dry vegetation.

- Well above normal temperatures with highs in the 70s Saturday
  through Tuesday.

- The next chance of rain arrives Tuesday night and Wednesday.

- Conditions hazardous for small craft through this evening on the
  Bay of Green Bay, and into early Saturday morning for the
  waters of Lake Michigan.

&&

.DISCUSSION...
Issued at 330 AM CDT Fri Oct 18 2024

Short Term...Today...Tonight...and Saturday

Quiet weather persists into tonight as high pressure ridge from
the Ohio Valley to lower Great Lakes slowly drifts southeast
keeping approaching cold front in the northern plains off to the
west. This front will come as close as northwest Wisconsin to Lake
Superior by Saturday afternoon which could produce a few light
showers over the far north. At the least, we`ll see more clouds on
Saturday than have occurred the last few days.

Today will be similar to yesterday with mostly sunny skies, though
winds in the mixed layer will not be as strong and temperatures
will be around 5F warmer across the board. Expect peak wind gusts
to 25 mph from central to north-central WI in the afternoon.
These areas will also have the lowest humidity values at 23-28
percent. The warm temperatures, gusty winds and lower humidity in
these areas, especially where vegetation is dry and soils are
sandy, will result in another day of elevated wildfire conditions.
Winds diminish this evening, but will not completely go calm. Lowest
temps in the upper 30s will be over eastern areas closer to influence
of Ohio Valley high pressure. Readings over the west and north will
be warmer due to steady wind ahead of approaching cold front.

On Saturday, cold front to the west never quite makes it here as
stronger flow aloft/shortwave trough deflects more to the north
than east. Even so, soundings show increasing clouds and some lift
in that moist layer even as low-levels below 5kft remain dry. A
few light showers or more likely sprinkles may develop over the
north. Most spots will remain dry. Even with the increasing clouds,
warm air advection in the mixed layer results in highs reaching
the lower 70s from central to east-central/northeast Wisconsin,
while readings remain in the mid 60s north with more clouds and
the small precip chances. No matter how you slice it, looking at
well above normal highs for mid October as normal highs are mainly
in the mid 50s.

Long Term...Saturday Night Through Thursday

The main highlights in the extended period are the potential for
precipitation Tuesday into Wednesday, well above normal temps
Sunday/Monday, and a return to more normal temperatures around the
middle of next week.

Precipitation...
The upper pattern is expected to evolve from a highly amplified
pattern to a more zonal one as a cutoff low over the Rockies fills
in and merges again with the northern stream early next week. The
remnants of the cutoff low will arrive in the western Great Lakes
Tuesday, but the remaining forcing, moisture, and precipitation
associated with it will likely remain to our south, keeping early
Tuesday dry. Behind the merging low however, a secondary trough
is expected to arrive from the north Tuesday night, which will
serve as a better focus for precipitation overnight into Wednesday
morning. The southern most extent and coverage of showers does
remain a bit uncertain at this time however, as dry air in the
lower levels will still need to be overcome, especially in areas
of central to east-central Wisconsin. Behind the cold front, dry
conditions return for the rest of the forecast period.

Temperatures...
The warmest temperatures in the forecast period will be on Sunday
and Monday, with highs in the 70s both days as we remain in the
strong southerly flow across the area. Then as the low mentioned
above merges and the cold front rolls through, expect a return to
near normal, with much of the area seeing highs back in the upper
40s to middle 50s in the middle of next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 638 AM CDT Fri Oct 18 2024

VFR flying conditions continue through the TAF period at 12z
Saturday. Beyond this, though it stays VFR there will be more mid
and high clouds later Saturday, especially over northern WI.
Until then, only clouds will be some increasing cirrus from the
west. The main concern will be surface wind gusts along with LLWS.

Have some LLWS this morning at CWA/AUW/RHI. Once this ends mid
morning, southerly sfc winds will become gusty again at all the
TAF sites. Less than 20 percent chance that gusts exceed 25 knots
this afternoon at any of the TAF sites. As winds decrease this
evening, another round of LLWS will develop at RHI, AUW and CWA,
but the LLWS should end late tonight as the low-level jet weakens.

&&

.MARINE...
Issued at 330 AM CDT Fri Oct 18 2024

Small Craft Advisory remains in effect for the bay into this
evening and for the nearshore waters of Lake Michigan into early
Saturday morning. Gusty south/southwest winds will build waves to
2 to 4 feet on the bay, and 4 to 7 feet on the lake.

Beyond Saturday morning, steady southwest winds will keep some
choppiness going for the waters of Lake Michigan the rest of the
weekend. And it is possible we could at least briefly see Small
Craft Advisory criteria reached again later Saturday into Saturday
evening off Door County and Washington Island as waves briefly build
over 4 feet.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....JLA/Uhlmann
AVIATION.......JLA
MARINE.........JLA