892
FXUS63 KGRB 242318
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
618 PM CDT Tue Sep 24 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

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

- Next chances for precip arrive Sunday into Monday as the
  remnants of what is expected to become Hurricane Helene traverse
  the Midwest.

&&

.DISCUSSION...
Issued at 218 PM CDT Tue Sep 24 2024

Short Term...Tonight and Wednesday

A surface low moving from northwest Indiana to central Lower Michigan
will produce clouds across the lakeshore counties and parts of the
Fox Valley tonight, while scattered to broken clouds dissipate further
west. Clearing skies should allow for the ground fog mostly east
of highway 51 and west of the bay. Lows tonight will be around five
degrees higher than normal.

Surface ridging will move into Wisconsin Wednesday, and bring sunny
skies and mild temperatures, once any ground fog dissipates. Highs
will be 5 to 10 degrees higher than average,.

Long Term...Wednesday Night Through Tuesday

Expect the beginning of the extended to be warm and dry as a rex
blocking pattern maintains ridging over the eastern CONUS. Focus
will then turn to precip chances this weekend into early next week
as the northwestern periphery of what is expected to become
Hurricane Helene makes its way up into the Midwest. However, there
is still considerable uncertainty with storm track given the
extended lead-time.

Precip chances... As the rex block gradually breaks down and
shifts to the east, ensembles show Helene becoming a post-
tropical depression as it propagates across the Ohio River Valley
Sunday and Monday. There are still some questions about how much
moisture will be able to make it up into Wisconsin during this
time, with current model guidance appearing pessimistic about any
moisture transport north of Highway 10. Better chances for
rain/storms look to be Monday evening through Tuesday as a
Canadian low drags a cold front southeast through the Great
Lakes. Models show the surface low ingesting residual moisture
from Helene, resulting in around 1.75" PWATs (~2 to 3 standard
deviations above average) extending across eastern Wisconsin out
ahead of the front. There is still considerable spread in precip
amounts this far out, although there seems to be a signal for
heaviest rainfall occurring near/along the lakeshore. Some
rumbles of thunder cannot be ruled out across central Wisconsin
Monday evening as MUCAPEs approach 200 J/kg, although storm
coverage is expected to be isolated.

Temperatures... Summer-like conditions are expected to make a
brief comeback for the latter half of the week as 850 mb
temperatures rise to between 15 and 17C Friday and Saturday.
Subsidence from high pressure will thus result in highs running
around 10 degrees above average, ranging from the mid to upper 70s
across the forecast area. This being said, temperatures may
underperform Friday and Saturday as the cirrus shield from Helene
spreads over the region. Post-frontal temperatures will then drop
down into the low to mid 60s Tuesday afternoon, reading near to
slightly below average for late September.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 618 PM CDT Tue Sep 24 2024

A surface low moving from southern lower Michigan to northern Lake
Huron will bring clouds with MVFR ceilings at times south of a
SUE to ATW to Y50 line tonight. Stratocumulus clouds with bases
between 4000 and 6000 feet will gradually dissipate around
sunset.

Ground fog is possible after midnight in an area roughly east of a
EGV to AIG to DLL line, and west of a SAW to EZS to STE line. The
fog will dissipate around 13z if it does form.

Sunny skies and good visibility is expected Wednesday as a ridge
of high pressure builds into the region.

&&

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

&&

$$

DISCUSSION.....RDM/Goodin
AVIATION.......Kurimski