Branch, Wisconsin Weather Forecast Discussion

544
FXUS63 KGRB 031714
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
1214 PM CDT Fri Oct 3 2025
Updated aviation portion for 18Z 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 18Z TAF Issuance
Issued at 1213 PM CDT Fri Oct 3 2025
VFR conditions are expected to prevail across all terminals
(KGRB, KATW, KMTW, KAUW, KCWA, KRHI) through the forecast period.
A weak cold front currently situated over the Upper Peninsula of
Michigan is expected to be the focus for isolated shower and
thunderstorm development this afternoon. However, convective
allowing models indicate this activity will remain north of the
forecast area, and probabilities are too low to include in the 18Z
TAFs. CIGS will consist of SCT mid and high-level clouds with no
impact on flight operations.
SFC winds will be out of the southwest and will increase through
the period as a low-pressure system over the Rockies tracks east
and the surface pressure gradient tightens. Expect sustained
speeds of 5-10 kts this afternoon and 6 kts or less tonight. South
winds will gusty up to 20 kts by the end of the taf period. Some
gusts to 25 kts are possible Saturday afternoon.
Marginal LLWS is possible overnight as southwesterly winds at
2000 ft increase to around 30 kts.
OUTLOOK...LLWS is possible again Saturday night with gusty south
winds continuing Sunday, potentially reaching 30 kts.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....Goodin
AVIATION.......MPC

NWS GRB Office Area Forecast Discussion