741
FXUS63 KGRB 161744
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1244 PM CDT Wed Apr 16 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Elevated fire weather conditions will be possible this afternoon
  due to relative humidity readings in the low to mid 20s,
  locally lower in sandy soil areas.

- Rain/embedded storm chances return Thursday night, continuing
  through Friday. Some storms Friday afternoon could become strong
  to severe.

&&

.DISCUSSION...
Issued at 230 AM CDT Wed Apr 16 2025

Short Term...Today...Tonight...and Thursday

GOES IR imagery showed low stratocu deck gradually scattering out
overnight as high pressure settled over the western Great Lakes.
Combination of clear skies and decoupled winds allowed for
typical cold spots in northern Wisconsin to get down into the
low 20s.

Return flow out of the south/southeast sets up this afternoon as
high pressure departs to the east, resulting in highs rebounding
into the mid to upper 50s inland of Lake Michigan. Minor fire
weather concerns will come into play during this time as an
abnormally dry airmass (10th percentile PWAT) sits and spins over
the upper Midwest.

Long Term...Thursday Night Through Tuesday

Forecast concerns continue to revolve around rain/storm chances
Thursday night through Friday, with potential for some stronger
storms Friday afternoon. Elevated fire weather conditions then
return over the weekend as high pressure settles in over the Great
Lakes and dries us out.

Rain/storm chances... Positively tilted upper trough and
attendant surface low trek through the upper Mississippi Valley
Friday morning, bringing first wave of showers within WAA regime
Thursday night. Modest instability (~300 to 500 J/kg MUCAPE)
accompanies the initial push of WAA out ahead of the warm front,
resulting in potential for some rumbles of thunder Thursday night
into Friday morning. Better instability (1,000+ J/kg MUCAPE) then
arrives Friday afternoon with stronger forcing along the cold
front, although storms will likely remain elevated in nature.
This being said, mid-level lapse rates approach 8 to 9 C/km across
east-central Wisconsin Friday afternoon with decent ascent within
the hail growth zone, so this would be a time to watch for hail
development were any storms to become strong. Storm coverage and
intensity remain uncertain, though will likely hinge on northern
extent of the warm sector, with several scenarios still in play
per ensemble guidance. ML severe weather algorithm currently shows
a 5 to 15% chance of severe storms developing in east-central
Wisconsin Friday afternoon (SPC Day 3 marginal risk), shunting
the higher probabilities further south and east with better
forcing. Additionally, periods of heavy rain will be possible
Friday afternoon as PWATs exceed one inch, with probabilistic
guidance showing a consistent signal (30 to 50%) for rainfall
amounts of 0.5". Locally higher amounts would be possible within
areas of convection.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1239 PM CDT Wed Apr 16 2025

VFR flight conditions expected through the TAF period, with
only an increase in high/mid clouds anticipated later tonight
into Thursday morning. No vsby restrictions expected.

LLWS will become a concern late tonight into Thursday morning,
as south winds aloft increase to 35 to 40 kts. The main concern
will be at the RHI, AUW, CWA and ATW TAF sites.

&&

.FIRE WEATHER...
Issued at 230 AM CDT Wed Apr 16 2025

Today... Elevated fire weather conditions, mainly driven by low
RHs, will be possible late this morning and afternoon. Said RHs
will plummet into the low to mid 20s north and west of the Fox
Valley beginning later this morning as high pressure dominates
and deep mixing to around 5k ft occurs. Sandy soil regions may
even get down into the upper teens. This being said, suspect that
a combination of fuel moisture and light winds should keep things
at bay.

This weekend... Fire weather concerns return this weekend with RHs
in the low to mid 30s and winds gusting 15 to 20 mph. However, fuel
moisture may once again be a hindrance to elevated fire
conditions due to recent precipitation.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......Kieckbusch
FIRE WEATHER...Goodin