385
FXUS63 KGRB 180011
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
711 PM CDT Fri Oct 17 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Warm through Saturday, with highs in the upper 60s to middle
  70s. Temperatures return back to normal beginning Sunday.

- Periodic showers and a few thunderstorms late this afternoon
  and tonight, then again Saturday night into Sunday morning.

- Breezy this afternoon with southerly gusts to 25 mph, and again
  on Sunday as northwest winds gust to 25 to 35 mph.

&&

.DISCUSSION...
Issued at 138 PM CDT Fri Oct 17 2025

Strong 990-995mb low pressure tied to negative tilted mid-level
trough lifting across Manitoba is pushing a weak cold front (more
so a wind shift) into western WI. A broken line of light showers
were along the front earlier, though they have pretty much
dissipated now. It is breezy and warm over northeast WI ahead of
the front. Under partly sunny skies, early afternoon temperatures
have already reached the low to mid 70s. Normal highs are in the
mid to upper 50s. As instability (SBCAPE) increases into early
this evening to 200-400J/kg, showers as close as central IA will
expand as they push into central and north-central WI. Even with
the projected meager instability, given stronger 500mb and 850mb
jets over the area, effective shear and helicity increase enough
that an isolated strong storm or two cannot be ruled out late this
afternoon into early this evening over central WI. 12z HREF 40+
dbz paintballs hint at this as well. Later tonight, showers will
diminish in coverage as they reach eastern WI. Rainfall amounts by
daybreak Saturday will mainly be less than one-quarter inch at
any location, though locations that see any storms will have a
better chance to exceed that. Rain exits to our east early on
Saturday. Most areas stay dry on Saturday and still relatively
mild as readings over eastern WI could reach the lower, maybe even
mid 70s.

Stronger cold front arrives Saturday afternoon through Saturday
night as a potent negatively tilted trough crosses the upper
Mississippi river valley and Great Lakes. Further, as southern
stream shortwave trough over the desert southwest today, phases
with the primary trough, cyclogenesis will occur with closed off
sfc low Saturday night over Ill and shifting to vcnty of northern
Ill/southwest MI by Sunday morning. Trend of the sfc low is still
farther east than what was shown a couple days ago, though most
recent model runs have not went any farther east. Moderate to
heavy rain will occur along and just west of the low, which at
this point continues to set up over Lake Michigan and into western
Michigan. Light to moderate rain will still impact eastern WI
late Saturday night through Sunday morning. Even so, chances of
seeing more than 0.50 inch in eastern WI remain less than 20%.
With the farther east trend of the low, probability of gale force
gusts over 35kt/40 mph are more focused farther into the lake away
from the shore. It will still be breezy though as gusts over the
land areas should still reach 25 to 30 mph on Sunday. Rain still
on track to taper off by Sunday afternoon, with dry weather
lasting through Monday morning.

The break in rain is brief though as another strong shortwave
trough and sfc low dig across the northern Great Lakes on Monday
night into Tuesday. Warm air advection will help develop showers
on Monday afternoon, with more showers possible in the stronger
cold moist advection regime behind the system on Tuesday. Tuesday
will be blustery with highs barely reaching 50 over eastern WI and
staying stuck in the 40s elsewhere. Rest of the week features small
chances for showers, before pattern becomes less active late in
the week. Temperatures will remain around normal for highs, with
low temperatures around freezing farther inland and into the mid
to upper 30s over eastern WI. Depending on whether winds can go
calm, there will be a potential for frost.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 710 PM CDT Fri Oct 17 2025

Isolated to scattered showers will continue across the region
through the evening and overnight hours, as a weak cool front
moves through, slowly shifting/exiting to the east Saturday
morning. Thunder is struggling to materialize due to the limited
instability. While a stray storm will be possible into early
Saturday, have removed the mention in the TAFs as chances for any
one spot to see a storm is under 15%. VFR conditions will drop to
mainly MVFR in the heavier showers and for a time near the weak
frontal boundary. Partial clearing behind the front may result in
low clouds and patchy fog developing central to north-central WI
08z-14z. Expect VFR conditions to then prevail late Saturday
morning and afternoon with a few fair weather cu and scattered
mid and high clouds.

As south surface winds ease early this evening and gusts are
limited due to reduced surface mixing, a low-level jet overhead
will result in a round of LLWS this evening into the early
overnight hours, ending from west to east. West/southwest winds
will gust up to 20 kts late Saturday morning and afternoon.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion