Birch, Wisconsin Weather Forecast Discussion

599
FXUS63 KGRB 041142
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
642 AM CDT Sat Oct 4 2025
Updated aviation portion for 12Z TAF issuance
.KEY MESSAGES...
- Very warm again today with high temperatures in the 80s to near
  90. Several record highs in jeopardy, including the potential
  for warmest on record for month of October at GRB.
- Conditions hazardous to small craft late this afternoon through
  early Monday morning.
- Gusty winds paired with very warm temperatures this weekend will
  result in increased fire weather potential.
- Rain chances return late Sunday across north-central WI, then
  impact all areas Sunday night through Monday night. The highest
  rain chances will occur Monday into Monday evening from central
  to east-central WI (40-60%).
&&
.DISCUSSION...
Issued at 329 AM CDT Sat Oct 4 2025
Broad upper ridge centered over the eastern CONUS will hold
through most of the weekend over the Great Lakes. Other than the
isolated storms early today over far northeast WI, rain chances
will not arrive until mainly Sunday night. In the meantime, we`ll
be basking in record setting warmth over much of the area and
increasingly breezy conditions which will lead to elevated
wildfire potential. For those looking for fall, sharp cooldown is
still in store early this week and we could see frost over
northern WI by Tuesday night.
Temperatures...Persistence forecast should work for today with
mostly sunny skies, deep mixing and similar 925-850mb temps to
yesterday. See no reason why highs will not make a run at 90
degrees over portions of the Fox Valley and into parts of central
WI. Mid to upper 80s elsewhere. If GRB reaches 89, it will set an
all time October record as the 88 yesterday tied that mark. After
a night where temps in the mid 60s will be what we should be
seeing for highs this time of year, another warm day will occur on
Sunday. Highs continue to trend up, though anything more than
isolated records look unlikely. Once the front moves through, it
is back to October with post-frontal temperatures dropping back
into the 50s and 60s to start the work week, with highs
potentially below average by midweek. As high pressure settles
overhead Tuesday through Wednesday, min temps dropping into the
lower to middle 30s will promote frost Tuesday night and Wednesday
night for northern into far northeast WI.
Winds/Fire weather...Increasing pressure gradient and stronger
winds aloft will be breezy to windy conditions this weekend.
Gusts this afternoon should reach 20-30 mph, strongest over
central and north-central WI. Even stronger winds occur on Sunday
with many areas seeing gusts over 30 mph by the afternoon. Risk of
seeing 40+ mph gusts is lower, but would be highest over central
to north-central WI based on expected mixing into 40-50 kt low-
level jet. The gusty winds, RH values as low as 30-35% in sandy
soil regions of central to far northeast WI, combined with drying
and curing fuels leads to increased fire weather concerns,
especially as the expected winds would support the potential for
power line fires. Per fire weather partners, fuels are not quite
ready yet as even as leaves are turning, they are still mainly on
the trees. Will continue to highlight in the HWO and through our
messaging on social media.
Marine...On Lake Michigan, status quo for stronger southerly winds
(as high as 20-25 kts with gusts 30-35 kts) and building waves
(as high as 6-9 feet) leading to a high-end Small Craft Advisory
starting late this afternoon and lasting into Monday morning. Only
change was to extend end of Small Craft until 7 am on Monday. On
the Bay of Green Bay, only marginal gusts 20-25 kts today near
Washington Island, so no headline. Greater risk and greater coverage
of 15-25 kts with gusts over 25-30 kts on Sunday, so we`ll eventually
issue a Small Craft Advisory for the Bay, just not yet. Once winds
shift northwest on Monday morning behind the cold front, they become
significantly lighter.
Rain/Storm chances...Weak moisture advection and enough elevated
instability was just enough to kick off storms over the Green Bay
area late last evening. Remnants of these are shifting across Door
County early this morning and will exit soon.
Dry the rest of today into tonight, then main change to the
forecast was to introduce small pops for showers and some storms
over north- central WI late on Sunday afternoon as tail of
shortwave lifting north of Lake Superior interacts with low-level
jet and increasing instability to develop isolated to scattered
showers. Decent agreement from available CAMs and short range
models, ensembles (e.g. HREF) to support increase in pops. After
this, cold front over the northern plains shifting east Sunday
night into Monday continues to support chance to low-end likely
pops in a fairly narrow band of showers and at least isolated
thunder. Greatest risk of rain for central to north- central WI
occurs Sunday night, with better chances for northeast, east-
central WI late Sunday night through Monday. Still a signal that
secondary wave rides along and north of front Monday night, but it
also still looks like most of the forcing for the next round of
showers (enhanced by right entrance of upper jet) will stay to the
south over southern/southeast WI and into central Great Lakes.
Total precipitation late Sunday through Monday mainly less than
0.25 inch. Probabilities of exceeding that amount have increased
to 40 percent in parts of central WI, but risk of seeing over 0.50
inch remain low, topping out at less than 20% over central WI.
Dry weather then through Wednesday, before return flow brings
chance for showers back to the region late next week. Model
agreement not great, so pops stay in slight chance range for now.
&&
.AVIATION...for 12Z TAF Issuance
Issued at 639 AM CDT Sat Oct 4 2025
Winds will be main concern for these TAFs conditions will be VFR
with scattered high clouds. SW surface winds less than 10 kts
increase to 10-15 kts with gusts to around 20 kts by late morning
and up to 20-25 kts this afternoon. Surface winds diminish early
this evening, though a few gusts of 15-20 kts could occur through
the night. SW LLWS of 35-40 kts develops from west to east through
midnight, lasting the rest of the TAF period.
LLWS ends on Sunday morning. However, surface winds will quickly
increase from the southwest, gusting to 25-30 kts at most of the
TAF sites by afternoon. Conditions will remain VFR.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....JLA
AVIATION.......JLA

NWS GRB Office Area Forecast Discussion