Nichols, Wisconsin Weather Forecast Discussion

904
FXUS63 KGRB 190023
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
723 PM CDT Thu Sep 18 2025
Updated aviation portion for 00Z TAF issuance
.KEY MESSAGES...
- Isolated showers and storms this evening, mainly central WI.
- Periodic chances for showers and thunderstorms are expected
  Friday into early next week. The severe weather threat remains
  low.
- Conditions hazardous to small craft will be possible on Lake
  Michigan waters south of Two Rivers Friday night into Saturday
  morning. There will likewise be increased potential for rip
  currents on Lake Michigan beaches along this section of
  shoreline.
&&
.DISCUSSION...
Issued at 157 PM CDT Thu Sep 18 2025
Short Term...Tonight and Friday
This afternoon... Radar continues to show returns popping over
northern and east-central Wisconsin this afternoon where
instability has been allowed to build in the vicinity of a cold
front. Any rumbles of thunder were confined to the southern Fox
Valley. Low-level moisture likewise continues to stream north of
the frontal boundary as a deformation zone associated with low
pressure over South Dakota takes residence over western
Wisconsin. Broken stratus/stratocu deck has persisted over much of
northeast Wisconsin as a result.
Forecast over the course of the next 24 hours remains volatile,
with several chances for low impact rain/storms existing across
the forecast area. Thunder potential will be on the rise mainly over
northern Wisconsin later this afternoon and evening as MUCAPEs
approach 1,000 J/kg, though coverage will remain scattered at best
as stability increases from the east. Better chances for
rain/storms then arrive Friday afternoon as an upper trough
interacts with a moisture corridor of PWATs around 175 to 200% of
normal. Brief periods of moderate to heavy rain will thus be
possible Friday afternoon and evening as the cold front sinks
south, especially if/where showers train over the same area. Post-
frontal temperatures then drop into the mid 60s across the
Northwoods Friday afternoon, while remaining in the mid to upper
70s in/around the Fox Valley.
Fog... Patchy fog will be possible late tonight into early Friday
morning along/north of Highway 29 as a low-level inversion traps
remnant moisture from recent rainfall near the surface. Any fog
should then quickly scatter out by daybreak as winds pick up out
of the east. Another possibility is that this moisture could
manifest as low stratus instead.
Long Term...Friday Night Through Thursday
A slow moving upper  trough will be the main driver for the
active weather over much of the extended, bringing another push of
warmer, more moist air into the region.
Active Weather...
As the upper trough moves eastwards, a push of warmth and moisture
will move into the region Friday night, bringing with it a chance
for scattered rainfall. Elevated instability during this period
ranges around 200-500 J/kg, which would support some rumbles of
thunder at times, but any stronger storms seem unlikely at this
time. Some isolated to scattered shower activity may then stick
around on Saturday before the next surge of instability arrives on
Sunday, bringing another round of more widespread precipitation to
the region. Instability parameters for Sunday are a little better
than the day prior, but do largely depend upon clearing for some
surface heating earlier in the day. If this occurs, thunder will
be more likely once again, but given the long skinny soundings and
relatively weak shear, the threat of severe weather remains low.
Finally, a stacked low pressure system is expected to develop over
the Central Plains next week, but the path of this low continues
to change. Current trends would take the active weather south of
our area, which would reduce any active weather impacts.
Temperatures...
High temperatures will hold fairly steady over the weekend into
next week, with high temperatures remaining fairly solidly in the
upper 60s to lower 70s.
Marine...
The incoming active weather for Friday night will likely also
bring some increasing winds and waves for the Friday night period,
which may pose a concern for mariners and beach goers.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 722 PM CDT Thu Sep 18 2025
Showers and storms at CWA and AUW to start. Also have some IFR
stratus off Lake Michigan at MTW. After the storms and low clouds
diminish early, conditions should remain VFR through midnight.
Eventually, still expect MVFR/IFR cigs to develop at most sites
early Friday morning as low-level moisture persists along with
light east-northeast winds. Whether or not these lower cigs manifest
as patchy fog or low stratus is uncertain, though localized reductions
in vsbys to MVFR will be possible regardless, especially where some
rain occurred this evening. Any patchy fog should scatter out by
daybreak Friday though as winds increase out of the east. Greatest
risk for additional showers and storms on Friday will be over central
and north-central WI especially in the afternoon. May include some
mentions for these sites via PROB30 with 06z TAFs.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....Goodin/Uhlmann
AVIATION.......JLA

NWS GRB Office Area Forecast Discussion