034
FXUS63 KGRB 230509
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1109 PM CST Mon Dec 22 2025

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 909 PM CST Mon Dec 22 2025

Still awaiting drizzle to form this evening into central and
northeast WI. Saw some earlier obs of drizzle in far southern WI,
but these never made it farther north. Last shot of moisture
advection in lowest 3kft on nose of subtle low-level jet occurs
through 06z/midnight. Based on current trends and latest CAMs,
have trimmed mention of drizzle to only Waushara County across
the Fox Valley and to the lakeshore. 00z CAMS still generating
trace to 0.01 inch of QPF, but in an even smaller area than where
we already trimmed pops. Cigs are lowering over southern WI to
around 1kft and dewpoint depressions are lessening, so probably
still a small window for the drizzle to occur. Perhaps as the
echos recently forming on MKX radar clips our area.

If the drizzle forms, air temps and temps from primary roads
indicate it would mostly be DZ instead of FZDZ, especially the
closer one gets to the lakeshore as ATW and MTW are currently
sitting at 37, while GRB is 33. Even so, untreated back roads
could still become slippery. Until we see the "whites of its eyes"
though, we`ll hold off on an SPS.

&&

.KEY MESSAGES...

- There is a chance (25-40%) of light drizzle or freezing drizzle
  late this evening across mainly eastern WI. Untreated roads may
  become slippery, depending on road temperatures.

- Above normal temperatures are expected through the work week,
  with highs expected to read above freezing.

- Confidence is increasing for a round of mixed wintry precipitation
  late Thursday evening into Friday. Travel impacts will be possible.

&&

.DISCUSSION...
Issued at 208 PM CST Mon Dec 22 2025

Another surge of WAA and the nose of a subtle LLJ will bring another
round of light wintry precipitation parts of central and eastern WI
this evening. With the mid-level WAA a more pronounced warm noise is
expected to develop this afternoon and evening likely leaving
freezing rain/drizzle as the main p-type this evening. Overall QPF
amounts are expected to be light, maybe a hundreths or two, however,
event those light QPF amounts could cause a glaze of ice on untreated
surfaces. Pinning down where exactly ice accumulations will occur
still remains a challenge as near surface temperatures will likely
hover right around freeze across central and east-central WI this
evening. Any one traveling this evening should be alert for slippery
road conditions and allow extra time to reach you destination.

Dry conditions should return to the region Tuesday as a ridge builds
over the central CONUS. The majority of ensemble global ensemble
members show a weak short-wave coming across souther WI Wednesday
evening which could spur on some rain showers from the Fox Valley to
the lakeshore. With thermal profiles warming during this time think
any freezing precipitation is unlikely.

500mb cluster analysis continues to show a wide range of possible
scenarios for a system arriving late on Christmas Day evening,
however, a signal for a messy mixed precipitation event has been
persistent now in the ensemble guidance for several forecast cycles.
Thermal profiles are most favorable for freezing rain north of a
Marshfield to Green Bay line. NBM probs show a 25% chance for at
least a glaze of ice north of this line late Thursday into Friday
morning. Impacts from this system may be exacerbated due to
increased post-holiday travel. Still a lot of details to work out
with this system, but if you plan to be on the road Thursday evening
or Friday morning keep up to date with the latest forecast
information and adjust travel plans as needed.

Temperatures... Consistent signal for above average temperatures
over at least the next week as height rises and periods of
southerly flow usher in a +20C anomalous airmass at 850 mb. Highs
will read above freezing for most through the end of the work
week, with some locations across central Wisconsin and the Fox
Valley even flirting with 40 degrees. Above freezing dewpoints
will accompany the warmer air, which, when paired with the
possibility of rain, could result in the development of widespread
fog/low clouds on Christmas.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1109 PM CST Mon Dec 22 2025

Patchy light drizzle and freezing drizzle will impact eastern WI
into the early overnight hours. Have included a mention at GRB/ATW
and MTW as observations are now indicating at least some drizzle
is reaching the ground.

MVFR cigs have developed late this evening. Expect these to last
through late tonight before scattering out. Brief IFR cigs may
occur over northern WI at RHI. On Tuesday, MVFR cigs over the
north will linger into the early afternoon. Otherwise, mid and
high clouds with VFR conditions will occur elsewhere through the
TAF period.

&&

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

&&

$$

UPDATE.........JLA
DISCUSSION.....GK
AVIATION.......JLA