734
FXUS63 KGRB 252310
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
610 PM CDT Wed Sep 25 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Widespread patchy fog, some locally dense, may impact the
  Thursday morning commute.

- Warm temperatures to prevail through the end of the work week,
  with highs running between 10 to 15 degrees above average.

- Expect a mostly dry weekend as residual moisture from Helene is
  shunted to our south and east. Next chances for precip then
  arrive Monday afternoon.

&&

.DISCUSSION...
Issued at 245 PM CDT Wed Sep 25 2024

Short Term...Tonight and Thursday

Relatively quiet conditions are expected for the rest of the
afternoon and evening, as mid-level clouds associated with a
passing upper trough axis depart the region.

Fog will be the main weather concern overnight, as conditions for
fog formation appear more favorable than last night. Therefore,
would expect areas of fog and some patchy dense fog, especially in
areas of central to north-central Wisconsin, west of the Fox
Valley. Low temperatures will be a couple degrees warmer than last
night, but still generally range from the middle 40s to the middle
50s.

Thursday will bring back sunny conditions, which will help mix out
the fog fairly quickly in the morning. The rest of the day is
expected to be fairly quiet and mild, with high temperatures
getting back into upper 70s to lower 80s.

Long Term...Thursday Night Through Wednesday

Model guidance has been trending toward a drier forecast for the
extended as remnant moisture from Hurricane Helene gets locked up
in the Ohio River Valley over the weekend. Additionally, cold
frontal passage Sunday into Monday looks to be mostly dry as
models show any moisture out ahead of the front being trapped to
our north.

Precip chances... Expect warm and dry conditions to prevail through
the weekend as a rex blocking pattern maintains ridging over the
upper Midwest. As upper-level flow flattens out toward the end of
the week, ensembles show Helene becoming a post-tropical cyclone
as it makes landfall over Florida and travels north along the
Eastern Seaboard. Not currently expecting much, if anything, in
terms of precip as dry continental air shunts any remaining
moisture from Helene off to our south and east. Next chances for
rain/storms then arrive Monday afternoon as robust troughing spins
up Canadian low pressure over Alberta. Not too impressed with
precip chances during this time as well given an abundance of dry
air and limited instability. This being said, a rumble of thunder
cannot be ruled out from central to north-central Wisconsin Monday
afternoon given sufficient mid-level lapse rates (~6.5 to 7
C/km).

Well below average precip over the past month paired with a
strong signal for more dry weather to come has resulted in
moderate drought conditions being introduced across northeast
Wisconsin. If the current pattern continues, drought conditions
are predicted to expand across the forecast area.

Temperatures... Anomalously warm 850 mb temperatures (~14 to 16C)
and subsidence from high pressure will result in the brief return
of summer-like temperatures through the end of the week. Saturday
looks to be the warmest day, with highs ranging from the mid to
upper 70s. Some locations across central Wisconsin may even see 80
before the week is over. Only caveat will be whether or not the
cirrus shield from Helene causes temperatures to underperform.
Post-frontal temperatures will then drop down into the mid 50s to
mid 60s on Tuesday, reading near to slightly below average for
late September.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 610 PM CDT Wed Sep 25 2024

Scattered cloud cover around 5000 feet will dissipate this evening
with the loss of daytime heating. Ground fog will be the main
concern for tonight, as cooler temperatures and clear skies allow
fairly widespread fog. The best chance for fog will be across
north-central Wisconsin and near the Lake Michigan shoreline, so
the lowest visibility forecast was included for these areas.

The fog should mix out a few hours after sunrise, with good
visibility and flying conditions expected the rest of the day on
Thursday.

&&

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

&&

$$

DISCUSSION.....Uhlmann/Goodin
AVIATION.......Kurimski