639
FXUS63 KGRB 091831
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
131 PM CDT Sun Jun 9 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Isolated sprinkles/showers across the north today. Next chance
  for storms arrives Tuesday PM with additional chances late in
  the week.

- Chilly tonight with the potential for patchy/areas of frost over
  north-central Wisconsin.

- Below normal temperatures today through Tuesday with a warm-up
  expected mid to late week.

&&

.DISCUSSION...
Issued at 405 AM CDT Sun Jun 9 2024

Fairly quiet conditions expected to start the week, then things
turn more active mid-late week as a parade of shortwaves will
bring periodic shower/storm chances to the region. Main forecast
concerns will be determining how widespread the sprinkles/showers
will get today, how cold it gets tonight, how warm it will be
later this week and timing/strength of the mid-late week systems.

Shower/Storm Chances & Clouds/Winds:

A dry start to the day is expected with sunshine for much of the
area. But clouds will be invading from the north through the
morning as an upper jet drops south of the region, a shortwave
will rotate south across the state through the day. This, along
with colder air aloft and weak lift in the mid-levels, should
generate a few sprinkles or showers, mainly over northern WI. Some
of the sprinkles could sneak further south than models depict.
Models do not generate any measurable precip today, but would not
be surprised if we can squeeze out a hundredth or two somewhere
over the north. No thunder is expected as instability will be near
zero. Northwest winds will be a little on the breezy side later
this morning and afternoon, with gusts of 20 to 30 mph. Look for
skies to clear from north to south late this afternoon and early
evening.

Next chance for showers arrives Tuesday afternoon and evening
ahead of a quick moving shortwave and front. Forcing and moisture
look pretty narrow/brief, so not expecting a long period of
showers or significant rain totals. Instability looks very
marginal, likely under 300-400 J/kg. So a few storms will be
possible, but no severe storms are expected.

Fast, zonal flow over the northern CONUS will allow the next
shortwave and frontal boundary to arrive later on Wednesday.
Models hinting at a complex of storms forming somewhere west of
the area and spreading E/SE through the region. But due to timing
and strength differences, it will remain difficult to pin down
any details on how things will play out. With building instability
and shear, severe weather concerns will need to be monitored.

As the upper flow turns to the southwest late in the week and next
weekend, additional chances for showers and storms look to arrive,
but quite a bit of uncertainty exists as to when the better
chances arrive as a lot has to play out ahead of this system.

Temps / Frost Potential:

An impressive push of CAA arrives today, with 850mb temps dropping
to between 3-7C, resulting in below normal temps. This supports
highs ranging from around 60 in far north-central WI to the lower
70s in the south. If clouds are a little slower to clear, temps
will likely not make it out of the 50s over the north.

As skies clear and winds diminish tonight, temps will fall into
the 30s and 40s. Where winds go calm over north-central WI, some
areas/patchy frost is likely. MET MOS guidance still showing a low
of 32F at Land o Lakes, which is likely a good indication of how
low temps could fall. A Frost Advisory may be needed for far
north-central WI.

Near to slightly below normal temps are expected Monday and
Tuesday, then look to climb back above normal on Wednesday and
Thursday. Still some question to just how much we warm up at the
end of the week as any complex of storms could keep more clouds in
the region, along with keeping the front further south.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 131 PM CDT Sun Jun 9 2024

A layer of overcast cloud cover will move across the region this
afternoon and evening. This will bring some MVFR ceilings across
northern WI but may also briefly bring some MVFR ceilings to
portions of central to east-central WI. The clouds will move off
again in the early overnight period, bringing back good flying
conditions and VFR skies for the remainder of the period.

Northwest winds remain gusty through this afternoon as well, but
will become lighter overnight.

&&

.MARINE...
Issued at 405 AM CDT Sun Jun 9 2024

Another marginal set up for conditions hazardous to small craft
today as north to northwest could gust to around 25 kts. Stronger
winds aloft early this morning, but stability issues will likely
hamper the winds making it to the surface. This afternoon, better
mixing is expected, especially near the shore, but winds aloft
come down a little. Colder air will aid in better mixing through
the day, with water temps in the 50s on Lake Michigan and 50s to
low 60s on the bay. Waves will stay under criteria, but it will be
quite choppy with waves of 1-4 ft. Leaned on the cautious side
and issued a Small Craft Advisory for this afternoon/early
evening.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......Uhlmann
MARINE.........Bersch