278
FXUS63 KGRB 310906
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
406 AM CDT Fri May 31 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Showers and isolated thunder over north-central Wisconsin this
  afternoon through Saturday (60-70 percent chance of rain). Lower
  chances for rain northeast to east-central Wisconsin (remaining
  dry until 20-30 percent chances arrive Saturday afternoon).

- Watching Monday for a chance of strong thunderstorms and
  locally heavy rainfall as a cold front crosses the region.

&&

.DISCUSSION...
Issued at 405 AM CDT Fri May 31 2024

Short Term...Today...Tonight...and Saturday

Eastward extent of showers and thunder through tonight is main
focus.

Sharp mid-upper ridge remains stout this morning from the corn
belt to Hudson Bay. Meanwhile, trough that forged across the
prairies of Canada the last two days is in the process of closing
off as it lifts to northern Saskatchewan and Manitoba by Saturday
morning. Net result is sfc low will become occluded over those
provinces through Saturday while upstream cold front over the
Dakotas gradually diminishes as it pushes into the western Great
Lakes. Showers through the period will be most favored over
north-central Wisconsin and least favored over east-central
Wisconsin from Green Bay/Appleton to Door County.

Today and tonight, scattered showers ahead of this front marked
well by low-level theta-e right along the boundary. Low-level
moisture reaches into mainly the northwest part of the area today
and there is at least a weak low-level jet aimed at our far northwest
cwa, Oneida into Vilas counties. Elevated CAPEs of at least a
couple hundred J/kg will support rumbles of thunder. Highs over
the northwest will be held down in the upper 60s to near 70. Highs
over the rest of the area should reach the mid to upper 70s except
right along the immediate Lake Michigan shore where south flow
will keep temps in the 60s. Showers will peak across north-central
areas late this afternoon through tonight. Actually good agreement
in HREF ensembles of seeing measurable rain amounts there (70-90
percent chance) while east of a Wisconsin Rapids to Iron Mountain
line those same HREF ensembles indicate less than 10 percent chance
of seeing *any* rainfall right through the night. Thus, appears a
sharp gradient from measurable rain to no rain is in store. Mild
night for all areas with low to mid 50s north and around 60 in the
Fox Valley.

On Saturday, greatest chances for rain and an isolated thunderstorm
will remain across north-central WI. Showers from a wave lifting
out of the southern Plains could also skirt along and south of
Oshkosh to Manitowoc line, though some guidance keeps northern
edge of this only from southeast WI into west central lower Michigan.
Locations that have best chance of staying dry Saturday will be
from Door County into Green Bay/Fox Cities, though if some rain
does occur for those spots it would be late in the day. For high
temps, plan on readings only around 70 for north- central and
Manitowoc southward. Mid 70s likely for the Fox Valley, especially
if it stays dry most of the day.

Long Term...Saturday Night Through Thursday

The main focus of the extended period will be on the late Sunday
night to Monday time period, when a low pressure system will bring
a cold front through the region, possibly resulting in some
stronger thunderstorms for our area.

Saturday night through Monday...
Lingering forcing from Saturday could sustain a few showers or
storms early Saturday evening but quieter conditions are expected
to return fairly quickly for the overnight hours. Sunday, a strong
shortwave will cross into the Northern Plains, bringing a plume
of warmth and moisture into the Dakotas and Minnesota, aiding in
the development of a surface low pressure system that remains the
anticipated weather maker. As of this forecast cycle, this axis of
greater instability and forcing remains well west of our area,
keeping the low and associated active weather out of our area
through Sunday evening. This makes for a much drier forecast for
the daytime hours of Sunday. That said, rain and storms will still
work their way east overnight through early Monday. While this
timing does not favor widespread severe weather, a stronger storm
or two may still possible, IF they can mix any of the 850mb 50kt
winds to the surface. As the low heads to our north Monday, the
slow moving attendant cold front will cross the region possibly
setting off a second round later in the day Monday. If we can
sufficiently destabilize again Monday afternoon, it will be this
second round that will have a better chance for stronger storms.

Rest of the forecast...
The next system may not be too long after the first in the
extended, with guidance bringing through another widespread round
of active weather sometime late Tuesday through Wednesday. This
system could bring another round of heavy rainfall, with initial
PWAT readings pushing 1.6+ inches of precipitable water, well
above normal for early June. That said, predictability remains
low for this system, so it will bear monitoring as we get into the
weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1023 PM CDT Thu May 30 2024

VFR flight conditions are anticipated through the TAF period,
except for possible MVFR ceilings in far NC WI Friday evening.
A gradual increase in cloud cover will occur in the northwest
part of the forecast area as a weakening cold front slowly
approaches Friday and Friday night. The front is expected to
generate scattered showers in NC WI Friday afternoon and evening,
and these should reach the RHI TAF site late in the afternoon.
Think some light showers will get close to AUW/CWA by early
evening, so will mention VCSH there.

Light SE-S winds are expected tonight, with moderate S-SW winds
expected on Friday.

There is a chance of borderline LLWS in far NC WI overnight, but
this is expected to remain NW of the RHI TAF site.

&&

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

&&

$$

DISCUSSION.....JLA/Uhlmann
AVIATION.......Kieckbusch