414
FXUS63 KGRB 051131
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
631 AM CDT Sun Oct 5 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- One last warm day today with highs ranging from the upper 70s to
  middle 80s. Gusty winds along with the very warm temperatures
  will result in increased fire weather potential.

- Turning much cooler early this week, with a frost or freeze for
  portions of central WI to northern WI Tuesday night.

- Conditions hazardous to small craft through Monday morning.

- Rain chances return this evening across north-central WI,
  impacting all areas tonight through through Monday night. Total
  rainfall mainly less than 0.25 inch. 20-40% chance of seeing up
  to 0.5 inch in parts of central WI.

&&

.DISCUSSION...
Issued at 253 AM CDT Sun Oct 5 2025

Southwest flow and mostly clear skies are observed early this
morning over WI well to the south of warm front and ahead of
northern Plains cold front. Temperatures across WI are more like
a summer night with widespread 60s to lower 70s. Many record warm
mins will be set today, and for some locations it won`t be even
close.

Showers and storms are ongoing this morning over far northern MN
into Canada in area of steeper mid-level lapse rates and higher
MUCAPE on nose of low-level jet. This instability streams
northward today, leaving minimal instability by time northern
plains shortwave trough and sfc low reach northern MN this
afternoon. So even though axis of 35-40 kt low-level jet moves in,
just a few showers may should make it into north-central WI late
afternoon. Otherwise, it will be a very warm and breezy day. Wind
gusts will reach 30-35 mph, with chance of seeing a few gusts to
40 mph over far north-central WI. High temps will be in the 80s
yet again, with warmest readings in the low to mid 80s from
central WI to far northeast WI and across the Fox Valley and
toward the lakeshore. Like the last few days, expect a sharp
gradient in afternoon temperatures near Lake Michigan. RH values
in the lower 30s this afternoon with the warm/breezy conditions
will lead to elevated wildfire conditions especially as based on
past events, the winds will be strong enough to lead to the
potential for power line fires. According to our fire weather
partners, heavier fuels are still not fully cured as leaves are
still primarily on the trees, which should temper the overall
threat. No fires were reported in the state yesterday, though
winds will be stronger today.

As shortwave trough and 500mb jet lift to James Bay late tonight,
height falls over the western Great Lakes will allow cold front
in the plains to steadily shift across WI. Front will bring fairly
narrow swath of showers and isolated thunder west to east, impacting
much of central and north-central WI this evening, but not reaching
far northeast WI, the Fox Valley and east-central WI until late
tonight (after 3-4 am). Rain will begin to taper off over north-
central WI by that time. MUCAPE with the front is minimal, maybe
a couple hundred J/kg. Given limited instability and sheared out
dynamics, isolated thunder seems to be the ceiling. Higher pop,
relatively lower QPF with the front providing the main forcing.
Main push of showers shifts east/south on Monday morning, but
lingering lighter showers may continue to affect southeast CWA
from Fox Valley to the lakeshore. Temps will fall off late tonight
with readings north-central down into upper 40s by daybreak. Temps
will still be above 60 east-central with the front just arriving
there around daybreak Monday.

Front settles southeast of east-central WI by early afternoon.
Another round of more concentrated showers could develop Fox
Valley to the lakeshore in the afternoon as secondary wave lifts
along the exiting front. Not expecting any thunder as whatever
weak instability is present will have been shoved well to the
south of the area. The cooler temps will be noticed by all with
highs in the lower 60s north and mainly mid 60s elsewhere. Even
though the temp drop with the front is significant, northwest
winds on Monday look light, with gusts less than 10 mph at most
locations.

Outlook beyond Monday...Front is still close enough to keep
chances for showers going on Monday night (especially in the
evening), though most of central to north-central WI will be far
enough away to keep the dry forecast going there. Cold air
advection persists aloft, but any lake effect clouds will stay
north of northern WI. Min temps Monday night may drop low enough
to support patchy frost. MUCH better signal for frost emerging on
Tuesday night with high pressure settling overhead leading to
mostly clear skies and light winds. Min temps already showing up
in the lower 30s. Drop this to the 25th percentile you could
easily see upper 20s over parts of northern WI. Even conditions
favorable for frost may extend well into central and far northeast
WI. Will continue to message the potential for frost/freeze on
Tuesday night. Light return flow from the southeast may complicate
things on Wednesday night, but mins in the mid 30s with patchy
frost possible.

Otherwise, Tuesday and Wednesday will see dry weather with highs
only really getting back to what they should be for early October
(low to mid 60s). Return flow brings a small chance for showers
late in the week. Not much rainfall expected and there remains
disagreement on extent of showers, so pops stay on the lower side
for now. What is better agreed upon is another warm up, with readings
back above normal by late this week and into next weekend, when 70s
may make a return. As dayshift noted, until we receive significant
wetting rain over the north, anytime we start to see well above
normal temps and breezy winds, fire weather will quickly become a
concern as the fuels continue to cure/dry out.

Boating Hazards: Small Craft Advisories remain in effect for Lake
Michigan and the Bay of Green Bay through late tonight (bay) and
Monday morning (lake) due to gusty south winds and high waves. On
Lake Michigan, waves have trended down, but will still build up
to 6 to 8 feet this afternoon. Once winds shift northwest on Monday
morning behind the cold front, they become significantly lighter.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 630 AM CDT Sun Oct 5 2025

VFR conditions prevail at all terminals through this afternoon
under mostly clear skies. Primary aviation concerns will be gusty
surface winds and significant low-level wind shear (LLWS).

Strong low-level jet results in LLWS of 40+ kts through mid-
morning. After this, surface winds will increase, with gusts
25-30 kts possible this afternoon. Gusts may exceed 30 kts for a
few hours at RHI. A period of LLWS is once again expected this
evening as a cold front approaches from the west and sfc winds
decrease.

A cold front will bring rain showers and possibly a thunderstorm
to central and north-central Wisconsin this evening. This activity
is expected to weaken as it tracks towards east-central Wisconsin
and the lake late tonight into Monday morning. Retained the PROB30
groups this evening CWA/AUW/RHI as the rain first arrives. Eventually
prevailing showers will spread west to east, impacting all terminals
for a period of 3-6 hrs. Cigs will stay VFR as the rain moves
through, then lower to MVFR as the rain begins to taper off.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA