529 
FXUS63 KGRB 031130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Fri Oct 3 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Temperatures warm through the weekend, peaking in the mid to 
  upper 80s Friday and Saturday afternoons. Several record highs 
  will be in jeopardy both days. 

- Conditions hazardous to small craft are expected Saturday 
  afternoon through early Monday morning.

- Gusty winds paired with near record temperatures will result in
  increased fire weather potential Saturday and Sunday.

- Most locations stay dry until Sunday night with the arrival of a  
  stronger cold front. Chances for isolated to scattered showers 
  then last through Tuesday afternoon.

&&

.DISCUSSION...
Issued at 205 AM CDT Fri Oct 3 2025

Persistence forecast more or less continues, with the main focus
being potential for record-breaking high temperatures this
afternoon and Saturday. Attention then turns to increasing winds
over the weekend, bringing with them elevated fire weather
concerns and hazardous marine conditions. Most recent suite of 
medium/long-range model guidance remains pessimistic about rain 
chances over the weekend.

Temperatures... At this point, pretty confident in saying that at
least a couple locations are likely to break record high 
temperatures this afternoon, and again Saturday afternoon. 925 mb
temps are progged to read between 22 and 24C both days, which, 
when paired with subsidence from thermal ridging, will likely 
translate to surface temps reading in the mid to upper 80s for
many. Few to scattered cloud cover should also allow for 
effective warming at the surface, further increasing forecast 
confidence. Little to no recovery is expected Friday and Saturday 
nights, with lows notably only making it into the low to mid 60s 
in/around the Fox Valley (record high mins?). Post-frontal
temperatures then drop back into the 50s and 60s to start the 
work week, with highs potentially falling into below average 
territory by mid-week.

Winds/fire weather... Pressure gradient tightens up over Wisconsin
beginning Saturday afternoon, with coincident 40 to 50 knot LLJ
spelling out potential for deep mixing and increasing winds. 
Widespread surface gusts of 30 to 35 knots look to be possible, 
especially Sunday afternoon. When combined with little to no 
precip and record high temperatures, elevated fire weather 
concerns begin to come into play. RHs bottom out in the low to mid
30s Sunday afternoon, mainly in the sandy soil regions of far 
northeast Wisconsin. These areas will be well within the 
thresholds for power line fires during this time, especially as 
leaf litter continues to fall and finer fuels start to dry out. As 
it stands now, the forecast Fire Danger Rating sits at "High" to 
"Very High" for most of northern Wisconsin both Saturday and Sunday. 
As such, will continue to hit the messaging a little harder for 
power line fires in subsequent products.

Marine... Pretty slam dunk for a prolonged period of marine 
headlines this weekend as robust southerly winds build waves on 
Lake Michigan to 4 to 6 ft on Saturday, and near 10 ft Sunday 
afternoon. Less slam dunk on the Bay, though if trends hold, small
craft conditions will be possible at times. Winds may occasionally
gust to near gale force on Sunday, especially up by Death's Door.
Maintain that preliminary headline timing would be Saturday 
afternoon through early Monday morning.

Rain/storm chances... Decaying cold front is still progged to clip
northern Wisconsin this afternoon, bringing with it a slight 
chance for an elevated shower or two. A modest pool of 
instability (~500 to 600 J/kg MUCAPE) gathers ahead of this 
boundary as weak low-level moisture transport makes its way into 
far northeast Wisconsin, resulting in potential for isolated 
thunder during this time. However, any shower that does go up will
have to contend with a massive reservoir of dry air as high 
pressure sits and spins over the eastern CONUS. Blocking pattern 
then breaks down late this weekend, as robust troughing over the 
Intermountain West ejects a shortwave into the upper Mississippi 
Valley as a cold front sweeps east. Deeper moisture behind the 
front still looks to be an issue, with most AI models keeping the
main swath of precip off to our south. Suspect that any shower 
activity will be sheared out regardless as 850 mb LLJ sits over 
eastern Wisconsin. Probabilistic guidance now shows chances for 
receiving 0.25" of rain at around 30 to 40% over east-central
Wisconsin through Monday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 620 AM CDT Fri Oct 3 2025

Fog has once again been held down this morning by light mixing at
the surface and SCT altocu, so have withheld any mention of BR 
from the TAFs. Otherwise, VFR conditions are expected through near
the end of the TAF period. Some pop-up showers will be possible 
across northern Wisconsin this afternoon as weak instability pools
out ahead of a stalled boundary, though thunder chances remain 
minimal. Best chances for showers would be up by RHI, though have 
refrained from adding a PROB30 group due to low confidence and 
sparse shower coverage.

Winds will be predominantly out of the southwest at around 5 to 10
knots, with gusts to 15 knots during the afternoon. LLWS may
briefly become a concern near RHI early Saturday morning as a 35
to 40 knot LLJ sits over northwest Wisconsin, though was too far
out in the forecast period to warrant including in the TAF.

&&

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

&&

$$

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