455
FXUS63 KGRB 101735
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1235 PM CDT Mon Jun 10 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Light showers are possible late Tuesday morning and afternoon,
  especially over northern WI. There is a chance for a few storms
  late Tuesday afternoon/evening as well, but the severe threat
  is very low.

- A more widespread round/complex of storms will be possible
  Wednesday night into Thursday, but confidence is low it track.
  Threat for severe weather needs to be monitored.

- Slightly below normal temperatures today and Tuesday with a
  warm-up expected mid to late week.

&&

.DISCUSSION...
Issued at 428 AM CDT Mon Jun 10 2024

Quiet weather on tap today then we enter a fairly active pattern for
the rest of the week and possibly into the weekend. Main forecast
challenges will be timing best chances for showers/storms, assessing
the severe threat, and temps. Uncertainty regarding subtle/mesoscale
features will make it hard to pin down details this far out. No
changes planned for the Frost Advisory which expires at 7AM this
morning.

Shower/Storm/Severe Chances & Clouds:

There will be lots of sun today as surface high pressure builds
across the western Great Lakes. High clouds will increase
overnight into early Tuesday, with clouds thickening Tuesday
morning as a quick moving shortwave and front approach from the
west. These features, along with a ribbon of moisture, will bring
a broken area of showers to parts of the area late Tuesday
morning and afternoon, highest chances over northern WI. Moisture
is pretty meager and forcing is weak, so the rain will be on the
light side. Zero instability through at least 5pm, so no thunder
is expected during the day. A secondary area of showers and storms
will be on the heels of the first one, with a ribbon of
instability (500-1000 J/kg) and bulk shear of 25-35 kts pushing
east across the state. This pool of instability will be waning
late in the afternoon and evening as the isolated/scattered storms
arrive, which will keep the the severe threat very low (a little
higher to our west where SPC has the marginal risk), but some
brief gusty winds are possible as the storms weaken as soundings
showing 30-40 kt winds aloft (highest threat across central WI).

Another chance for showers and storms arrives late Wednesday into
Thursday morning as a fast moving shortwave within the zonal flow
crosses the region. Models continue to show/hint at a complex of
storms forming in association with this shortwave and weak frontal
boundary, somewhere west of the area and spreading E/SE through
the region. Still some timing, placement and strength differences,
so it will remain difficult to pin down any details. That said,
while severe parameters are better to our west, building
instability and shear in our area and the possibly of an
organized complex of storms making a run at our area, will bring a
marginal/slight risk for severe weather. Will not hit the threat
too hard just yet in messaging do to the uncertainty, but the
threat will be monitored.

As the upper flow turns to the southwest this weekend, additional
chances for showers and storms look to arrive with a least one
main shortwave crossing the region, but still uncertainty on
strength/timing this far out.

Temps / Humidity:

After a chilly start to the day, especially across north-central
WI where temps fell into the 30s, nearly full sunshine will allow
temps to climb quickly in the morning hours. 925mb temps climb to
between 12-16C this afternoon which will support highs topping
out in the upper 60s to lower 70s (with the warm spots touching
the mid 70s) which is slightly below normal. It will not be as
cold tonight with lows dropping into the upper 30s over far
northeast WI and into the 40s elsewhere. Could get some patchy
frost near the MI border. Slightly warmer temps are expected on
Tuesday, but should remain a touch below normal. Return flow sets
up across the region on Wednesday as the high departs to our
east, allowing temps to climb mid- week. Warmest days of the week
will be Wednesday or Thursday with above normal temps expected.
Humidity levels will be on the rise mid- week as well, with
dewpoints climb into the 60s. Still some question to just how much
we warm up as any complex of storms could keep more clouds in the
region, along with keeping the front further south. But latest
guidance has 925mb temps getting to at least 20C, which should
allow highs to get into the upper 70s and lower 80s. Some guidance
has 925mb temps closer to 23C which would support highs further
into the 80s. Another surge of warmer/hot? air will arrive this
weekend, with highs in the 80s likely, with a 90 even possible if
the warmer guidance comes to fruition.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Mon Jun 10 2024

Wide open VFR conditions this afternoon through tonight. North
winds will gust to 15-20 kts early this afternoon at GRB/ATW/MTW
but winds diminish by late afternoon.

Cold front moving in from the west on Tuesday will bring thickening
and lowering mid clouds, but conditions through end of TAF period
will remain VFR. Showers will then shift west to east across the
region Tuesday afternoon through Tuesday evening. Only a small
chance of thunder with this system for the TAF sites as higher
instability remains over Minnesota and west to southwest Wisconsin.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......JLA