437
FXUS63 KGRB 181145
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
645 AM CDT Sun Aug 18 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Hazardous conditions for small craft are expected through late
  tonight. A Small Craft Advisory remains in effect.

- Small chances (less than 25%) for some sprinkles/showers today
  and Monday, along with some elevated smoke arriving tonight and
  Monday.

- Otherwise, quiet weather conditions and near-normal temperatures
  in the middle 70s to lower 80s are expected through much of the
  upcoming week.

&&

.DISCUSSION...
Issued at 329 AM CDT Sun Aug 18 2024

Short Term...Today...Tonight...and Monday

Drier and quieter weather arrives across the region today into
Monday. Main forecast concerns will be some small/subtle chances
for showers/sprinkles, fog/smoke trends and winds/marine
headlines.

Shower Chances / Clouds:

Weak surface high pressure will slide into the Great Lakes, with
strong mid and upper ridging building across the northern Plains.
This will bring mainly dry conditions, but a few subtle things to
keep an eye on for possible shower development. First will be
today as cyclonic and moist flow will continue across the region.
This, combined with cooler flow (850mb temps of 9-12C) over the
warm waters of the Great Lakes (Lake Michigan around 21-22C) will
help produce some lake effect/enhanced showers/sprinkles, both
over northern/eastern WI. Activity already on MQT`s radar, so have
added some shower chances across eastern WI this morning, when
moisture is deepest. Downsloping should help the activity weaken
somewhat as it moves south. Have also kept a good amount of
clouds across the area through the morning hours, with the
greatest coverage over eastern WI. Skies will clear out later
today into tonight. Second chance arrives on Monday, as a weak
boundary drops south across the area and a weak ripple in the
upper flow pushes overhead. Have increased cloud cover and can`t
rule out a few showers. Looks like the "best" chance to see
something would be across central WI, where MUCAPE up to 500 J/kg
is forecast, would could be just enough energy to touch off a
shower. Will also need to monitor for some light lake
effect/enhanced activity, over far northeast/eastern WI, as 850mb
cool by a couple/few of degrees. Have kept PoPs under 15 for now,
but some higher PoPs may need to be added. Luckily, anything today
or Monday would be light in nature and have no impacts.

Winds / Marine Headlines:

As better mixing begins after sunrise, north winds will gust to
20 mph, but the highest winds aloft push across the area this
morning, so winds look to die off this afternoon. On the Bay and
Lake Michigan, not ideal mixing conditions as air not that cold
aloft to really enhance better mixing, but gusts to around 25 kts
are expected continue today into this evening, then diminish
overnight. Waves of up to 4 feet are expected. A Small Craft
Advisory remains in effect. May be able to trim off a little at
the end, but won`t make any changes yet. The offshore nature of
the wind will not require any Beach Hazard Statements.

Fog / Smoke:

Fog has remained in check across most of the area early this
morning due to the lingering clouds and winds of 10-25 kts just
off the surface. Could have some very patchy fog across central
and north central WI through around sunrise where skies stay
clear. Any fog would burn off quickly after sunrise. Ground fog
is possible again late tonight across north central WI, but
boundary layer winds should help keep it very patchy.

Looks like we will have to contend with some smoke late today and
Monday, making for a hazy sky, as the HRRR/RAP show a large batch
of smoke spreading south into the western Great Lakes. Currently
expecting little to no impacts at the surface, but some subsidence
could help bring the smoke closer to the surface. If the smoke is
thick enough, it could hold down temps on Monday as well.

Temps / Humidity:

Temps will be pretty close to normal today into Monday. Highs are
forecast to be in the mid 70s to around 80. Lows tonight will
drop mainly in the 50s, with a few cooler spots likely in north
central WI and some warmer readings near Lake Michigan. A touch of
humidity will remain across mainly eastern WI today, otherwise it
will be less humid as dewpoints drop in the 40s/50s.

Long Term...Monday Night Through Saturday


Low impact weather remains expected through next weekend thanks to a
beefy upper ridge centered over the middle of North America.   The
medium range guidance shows a weak shortwave impulse suppressing the
ridge across the region during the Thursday-Friday time frame, when
very low chances of rain will be in the forecast.

Then the ridge builds again late in the week when temperatures will
be on the rise.  While the NationalBlend put in low precip chances
(less than 25%) into the forecast, predictability of precip Friday
through next weekend is low.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 645 AM CDT Sun Aug 18 2024

A mix of IFR/MVFR/VFR conditions prevailed early this morning as
large patches of low clouds moved across the area. Very patchy
ground fog across central and north central WI will burn off
quickly after sunrise. Look for the IFR/MVFR low clouds to stick
around this morning, but a slow improvement/scattering out of
ceilings is expected through the day. A stray shower/sprinkle
will be possible across eastern WI, but will not impact aviation.

North winds are expected today, with gusts to around 15 kts,
locally higher near the bay/lake. Winds will decrease this
afternoon into tonight and remain mainly out of the north.

&&

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

&&

$$

DISCUSSION.....Bersch/MPC
AVIATION.......Bersch