790
FXUS63 KGRB 232323
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
623 PM CDT Mon Sep 23 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Patchy frost and fog is possible across north central Wisconsin
  late tonight.

- Near normal high temperatures are expected on Tuesday before
  returning to above normal values midweek through next Monday.
  High temperatures could run as much as 10 to 15 degrees above
  normal.

&&

.DISCUSSION...
Issued at 335 PM CDT Mon Sep 23 2024

Short Term...Tonight and Tuesday

Main forecast concerns in the short-term are cloud/precip trends and
the potential for frost and fog development overnight.

This afternoon`s satellite imagery showed lake-effect clouds in far
eastern WI, with clearing skies further west across the rest of the
forecast area. Meanwhile, high clouds were just starting to lift
into east-central WI from shortwave energy to the south.

This evening and tonight...The weak mid-level shortwave will
gradually lift into the area and phase with a trailing mid-level
trough during this time period. There are some signals for isolated
showers or sprinkles to lift into east-central WI late tonight into
Tuesday, but forecast soundings indicate there may be too much dry
air in the low to mid-levels. Decided to only include very small
chances for showers and sprinkles. Otherwise, anticipate middle and
high clouds to spread over the entire forecast area with dry
conditions prevailing for the majority of the time. Despite another
night of cooler temperatures (lows in the middle 30s to low 50s),
the coverage of middle and high clouds in north-central WI, where
temps will be coldest, should hinder frost development. However,
there will still be a decent low-level temperature inversion and
light winds, which may allow for patchy frost and fog to develop in
some spots across northern WI.

Tuesday...With the mid-level trough overhead, anticipate similar
conditions to continue into Tuesday with a small chance for showers
or sprinkles in east-central WI and dry conditions elsewhere.
However, some clearing will occur across the western part of the
forecast area, while an onshore wind will help keep clouds over far
eastern WI. High temperatures will be similar to today (near normal)
with values ranging from the middle 60s to low 70s.

Long Term...Tuesday Night Through Monday

Normal highs start out this week in the upper 60s but by next
Monday are in the low to mid 60s. Good to recalibrate in terms of
temps as after a couple day hiatus, high temps will surge much
above normal again. A few locations will likely reach the 80
degree mark Thu-Sat.

Rain chances the rest of the workweek will be minimal. Outside
chance that an isolated light shower occurs early Tuesday evening
near the lakeshore (mainly Door County) as shortwave trough exits
across the central Great Lakes. Next chances for rain will not
occur until the weekend. However, these chances will be highly
dependent on fate of what will eventually become tropical system
Helene within the next couple days over the northwest Caribbean
Sea. There is good agreement that the system tracks north-
northeast and will make landfall across the eastern Gulf Coast
states by Friday. The remnants of the tropical system will then
dumbbell (aka Fujiwara) around the closed low present over
Arkansas late this week. Unsure how far north the system will be
propelled, but that potential along with deeper moisture advecting
into the western Great Lakes due to the system does result in
some models generating some showers with minimal thunder. Canadian
is most aggressive at this point compared to other primary
extended models and ensembles (ECMWF and GFS). Only minor change
was to delay pops on Friday night and slow the northward progress
of pops on Saturday.

The low chances of rain persist Sunday and Monday. Deep moisture
lingers with an approaching trough from the northern plains.
Ensembles are showing a consistent signal for at least small
chances for QPF, so thought best to leave those two days alone at
this point. Even with the potential for some rain, high temps
still look to be at least in the lower 70s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 623 PM CDT Mon Sep 23 2024

Mid and high clouds are expected to lift north across the region
later this evening and overnight. There is still potential for
patchy fog to develop by early Tuesday morning in central and
north-central WI, but the cloud cover may hinder this fog
development. Additionally, there is potential for a slight chance
of a shower or sprinkle across east-central WI late tonight into
early Tuesday morning. With confidence not very high in where the
showers may occur, have opted to only include a PROB30 group at
MTW.

&&

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

&&

$$

DISCUSSION.....Kruk/JLA
AVIATION.......Kurimski