819
FXUS63 KGRB 060423
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1123 PM CDT Tue Aug 5 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Near-surface wildfire smoke will continue to result in poor air
  quality through Wednesday morning. The Air Quality Advisory has
  been extended until noon on Wednesday.

- Temperatures and humidity slowly build throughout the week. Heat
  indices in the mid to upper 90s will be possible Friday and
  Saturday.

- Isolated to scattered thunderstorms will be possible Wednesday
  afternoon through Thursday, and again Saturday afternoon through
  Sunday.

- Increasing southerly winds and building waves may result in
  hazardous boating conditions on Lake Michigan over the weekend.

&&

.DISCUSSION...
Issued at 215 PM CDT Tue Aug 5 2025

Canadian high continues to influence us from the northeast,
recycling near-surface wildfire smoke over northeast Wisconsin
this afternoon into tomorrow. GOES satellite imagery currently
highlights thickest smoke over east-central Wisconsin this
afternoon, with obs showing minor reductions in visibility (6 to
7 SM). Otherwise, radar shows some weak returns over north-
central Wisconsin, although there are no indications of anything
making it to the surface.

Rain/storm trends... Surface high pressure departs to the
northeast on Wednesday, giving way to rain/storm chances Wednesday
afternoon through Thursday. Short to medium-range guidance
appears to capture the synoptic pattern relatively well, with
several shortwaves riding along westerly flow aloft. Isolated to
scattered storms are thus expected to develop within shortwave
regime and out ahead of an approaching warm front beginning
Wednesday afternoon as low-level moisture (1.5 to 2" PWATs) pools
over central and north-central Wisconsin and instability builds
during the afternoon (1,000 to 1,500 J/kg MUCAPE). Inverted-V
profiles combined with PWATs around 150% of average relative to
climo would support gusty winds and locally heavy rainfall with
any storms. This being said, deep-layer shear will generally be
held down to less than 20 knots, hindering any organized severe
weather. Influx of WAA from the southwest should then help put a
cap on any storm activity Thursday evening through Saturday
morning as 700 mb temperatures increase to around 13 to 14C.

Attention then turns to the potential for more robust storm
chances Saturday and Sunday, though there are still several
scenarios at play. An upper trough traverses the northern Plains
Saturday afternoon, garnering a more negative tilt as it retreats
into Ontario on Sunday. A weakening cold front likewise approaches
from the west Saturday and Saturday night in tandem with an
increasing LLJ and impressive moisture reserve (~2" PWATs).
Biggest hindrance to the forecast at this time centers around
timing of cold FROPA (Saturday night) and lack of shear, since we
certainly have enough moisture and instability present. As it
stands now, machine learning algorithms (CSU and NCAR) paint a
broad swath of 15 to 30% severe weather probs over portions of the
upper Mississippi Valley for Saturday.

Temperatures... Thermal ridge building over the eastern CONUS and
switch to southerly flow regime will result in heat and humidity
building toward the end of the week. Highs will plateau in the
upper 80s to low 90s Friday and Saturday, with dewpoints rising
into the upper 60s to low 70s. Result will be heat indices
flirting with headline criteria in the mid to upper 90s, though
this is wont to change depending on how convection behaves on
Saturday. Expect little to no overnight relief Friday night, with
lows only cooling into the low to mid 70s for most. Though we are
not currently anticipating the need for any heat-related
headlines, heat risk is expected to reach the "Major" category
inland of Lake Michigan Friday afternoon.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1123 PM CDT Tue Aug 5 2025

High clouds will stream in at times, especially north-central
Wisconsin, as a thunderstorm complex approaches from the west.
CAMs models break this apart before it reaches the region;
therefore, precipitation is not expected from this system. Near-
surface wildfire smoke is expected to continue impacting northeast
Wisconsin into Wednesday; however, it is not expected to be as bad
as previous days with VSBYs generally 5-6 SM. The surface smoke
should then lift north of the area around midday on Wednesday. A
SCT-BKN cu deck with bases around 4k ft is expected to develop
Wednesday afternoon.

CAMs once again show potential for patchy fog late tonight into
early Wednesday morning as winds decouple at the surface, though
coverage looks to be more sparse than previous mornings. If fog
were to develop near a TAF site, localized MVFR to IFR vsbys
would be possible. Confidence in fog at any TAF site is too low to
include in this set of TAFs.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......Kurimski