501
FXUS63 KGRB 100347
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1047 PM CDT Tue Jul 9 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Small chances (30% or less) for showers and thunderstorms
  Wednesday through Thursday. The severe weather threat is very
  low. Locally heavy rainfall will be possible.

- A warmer, and more humid, period develops for the weekend and
  early next week. Heat index values in the 90s are expected for
  much of the area by this weekend.

&&

.DISCUSSION...
Issued at 345 PM CDT Tue Jul 9 2024

Short Term...Tonight and Wednesday

Focus is on small potential for showers and thunderstorms, along
with fog and cloud trends.

Satellite imagery at 19Z showed cu development across the
Northwoods. There was some cu across central and east-central WI,
but this was also inhibited by the cloud shield coming from the
northern edge of Beryl remnants. Radar shows a few showers tried
to get going in Forest and Florence counties within the last hour,
but had trouble sustaining themselves.

Rest of the afternoon and evening...Isolated showers and
thunderstorms will be possible, mainly in northeast WI near the
Upper Michigan border, which is what recent meso model runs have
depicted. While there are some dynamics at play from a weak
shortwave and RRQ of upper jet, instability is only 400 to 800
J/kg and shear is exceptionally low, with 0-3km shear of 5-10kts,
and even 0-6km only around 10-20kts. Therefore, isolated showers
and thunderstorms are possible, but severe storms are not likely.
The main threat would be heavy rain as anything will be somewhat
slow moving.

Overnight...Patchy fog development is possible again. Winds will
be light and there is still moisture near the ground from recent
rains, but there will be more clouds tonight. Primary area to
watch for fog is across the Northwoods where more cloud breaks are
likely. Any fog would dissipate quickly after sunrise.

Wednesday...Very similar to today, with highs in the upper 70s and
low 80s, light winds, and a broken to overcast cloud layer.
Could see some isolated showers or non-severe storms in the
afternoon. The best chance is in central Wisconsin.

Long Term...Wednesday Night Through Tuesday

Main highlights from this forecast period revolve around small
precipitation chances for Thursday, a better chance for this
weekend, and the return of very warm and humid conditions late this
week into this weekend.

Precipitation...An embedded shortwave will phase with the main mid-
level trough focused over the western Great Lakes region late
Wednesday into Thursday. With little upper-level forcing present,
anticipate diurnally driven isolated showers and non-severe
thunderstorms to develop Thursday afternoon; however, most locations
are likely to stay dry. The departed trough will be replaced with
brief ridging, leading to dry conditions on Friday. Southwesterly
flow will set up for the weekend and coincide with a series of
shortwaves. Chances for showers and thunderstorms are anticipate
throughout the weekend as a result, with the best chances occurring
during the afternoon and evening when instability is peaking.

Temperatures...A gradual warm up is expected from Thursday through
the weekend due to the southwesterly flow lifting warmer, moist air
into the region. NBM probabilities favor temperatures to peak on
Sunday and Monday with probs for greater than 90 degrees in the 10-
20% range, with a few spots around 25%. While these temperatures are
very warm, any showers or thunderstorms would cause lower values. In
addition to the very warm temps, afternoon dew points will be in the
upper 60s to low 70s, resulting in humid conditions and elevated
heat indices (pushing the mid 90s on Sunday). Signs are pointing to
little recovery occurring overnight throughout the weekend and into
early next week as well, with lows in the 60s to low 70s. Will
continue to monitor how temperatures may fluctuate over the coming
days, but would recommend making adjustments to any outdoor weekend
activities to cater to the heat.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1046 PM CDT Tue Jul 9 2024

VFR conditions are expected through Wednesday, with a high
overcast across the southeast half of Wisconsin on the northern fringe
of former hurricane Beryl. Ground fog is possible in far north central
Wisconsin late tonight where there is less high clouds, generally north
of a Merrill to Iron Mountain line.

Some scattered cumulus clouds are possible below middle and high clouds
Tuesday. There could be some ground fog in the far north
Wednesday night.

&&

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

&&

$$

DISCUSSION.....KLJ/Kruk
AVIATION.......RDM