459
FXUS63 KGRB 241133
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
633 AM CDT Tue Sep 24 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Small precipitation chances over mainly eastern WI today into
  early tonight, then dry until the remnants of the developing
  hurricane in the Gulf of Mexico approach this weekend.

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

&&

.DISCUSSION...
Issued at 341 AM CDT Tue Sep 24 2024

Short Term...Today...Tonight...and Wednesday

Forecast concerns include small precipitation chances through this
evening, fog potential and temperatures.

WV imagery showed an upper trough axis near the Dakotas/MN border
early this morning, with a short-wave lifting north through WI.
At the surface, a weak inverted trough was noted over eastern WI.
Radar showed isolated to scattered showers across the region,
though abundant dry air in the 850-700 mb layer was preventing
much of this from reaching the ground. Additional showers
associated with a weakening cold front over MN were eroding as
they approached WI. Patchy fog was observed in parts of NC WI,
where there were some breaks in the clouds.

The short-wave will lift north this morning, and the inverted
surface trough is expected to gradually weaken during the day.
Will carry a chance of sprinkles across the whole cwa for the
first part of the morning, then focus slight chance/chance pops
across eastern WI for the rest of the day. Patchy fog in NC/C
WI should mix out early. Look for mostly cloudy skies to prevail
in eastern WI, while our western counties become partly cloudy.
High temperatures should reach the middle 60s to lower 70s.

A chance of light showers or sprinkles may persist into the
evening across east central WI, otherwise skies will become
partly cloudy as weak high pressure moves into WI. Patchy/areas
of fog should develop after midnight, especially over NC/C/far NE
WI. Lows will be mostly in the 40s and lower 50s.

On Wednesday, a pleasant early fall day is in store, as high
pressure brings abundant sunshine, along with temperatures
warming into the lower to middle 70s.

Long Term...Wednesday Night Through Monday

Dry and above normal temperatures are expected to end the work week.
Chances for precipitation return this weekend as the northern
periphery of what is expected to become Hurricane Helene spread over
the region, however, given that this storm is still in it`s
infancy there is considerable uncertainty with its track.

Precipitation...An upper-level ridge over the western Great Lakes
Thursday and Friday will keep the region dry to end the week.
Attention then shifts to what are expected to be the remnants of
Hurricane Helene. As would be expected with a tropical system 4 to 5
days out there is considerable uncertainty, but long range models
generally show Helene becoming  a post-tropical depression as it
meanders the Ohio and Tennessee Valleys Friday and Saturday. During
this time northward moisture advection may bring the next chance (20-
40 %)for showers and a few thunderstorms, mainly to areas south of
highway 29. LREF ensemble members show a large spread in expected
rainfall amounts for this weekend with the most aggressive members
showing a 5% chance for greater than 1 inch of rain through Saturday
night. Beyond this weekend there are signs another short-wave may
bring a chance for precipitation to the region early next week.

Temperatures...More summer-like temperatures are expected to return
for the back half of this week and this weekend as anomalously warm
850mb temperatures (1 to 2 standard deviations above normal) move
over the region. Highs are forecast to reach the low to upper 70s
each day with a slight chance (5-10%) for locations in the Fox
Valley and central WI to reach 80. However, if the cloud shield from
Helen spreads over the region Friday into this weekend high
temperatures may trend a few degrees cooler than currently forecast.
Overnight lows are also expected to trended warmer later this week
which for those locations that have not yet seen frost will keep the
growing season going until at least the end of September.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 629 AM CDT Tue Sep 24 2024

We are seeing some patchy MVFR ceilings early this morning,
especially near an inverted surface trough in eastern WI. Expect
the low clouds to persist through the morning, then gradually
rise to VFR by afternoon. In addition, scattered showers are
possible in eastern WI, with the best likelihood of occurrence at
the MTW TAF site. Expect clearing to occur as high pressure builds
into the region later this afternoon and evening, with areas of
ground fog developing overnight.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/GK
AVIATION.......Kieckbusch