299
FXUS63 KGRB 291956
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
256 PM CDT Sat Jun 29 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

-  Isolated thunderstorms over far northeast WI this afternoon.
   Stronger storms could produce gusty winds and small hail.

 - Conditions hazardous to small craft are possible into Sunday
   morning, then again Tuesday and Tuesday night.

 - Some rivers and streams will remain above bankfull through much
   of next week.

 - The next period to watch for heavy rain and stronger storms
   will be late Monday through Tuesday night.

&&

.DISCUSSION...
Issued at 254 PM CDT Sat Jun 29 2024

A few showers and storms into early this evening, then dry
through Monday. We remain in a very active pattern though so the
next chance for rain, possibly heavy, returns late Monday night
through Tuesday night. Some risk of strong or severe storms late
Tuesday as well.

Late afternoon into Tonight...Currently the tail of sharp
pinwheeling shortwave trough north of Lake Superior is combining
with MLCAPES up to 1000J/kg to generate cluster of thunderstorms
over eastern Upper Michigan. Isolated storms have tried to fill in
farther southwest across Bay of Green Bay and Door County, but so
far, these storms have had a hard time organizing. Perhaps this
is due to very weak mid-level lapse rates which are farther north
across Upper Michigan/Lake Superior. Re-enforcing cold front tied
to another sharp shortwave dropping across ND/western MN with
some punch is moving over northwest WI. Sharp wind shift noted and
temps upstream over MN are in the 50s. No instability for the
front to work with though, so though spotty showers may impact
much of central to north- central WI once the front moves through,
looks like we`ll be clear from any additional thunder threat. NW-
NNW winds will be gusty all areas in wake of the front. Temps
will take a tumble with readings by daybreak into the upper
30s/near 40 over the northwoods.

Sunday and Sunday night...Winds diminish on Sunday and we should
see wall-to-wall sunshine. Nice early summer day, though for some
it will probably be too cool with highs topping out low to mid
70s inland and mid to upper 60s near Lake Michigan. High pressure
settles across Sunday night. Light winds, clear skies and PWAT
down to 0.4 spell a chilly night over north-central WI, by spring,
or summer standards. MET guidance for LNL is 35. Could see
favored cold spots into the mid to upper 30s.

Monday through Tuesday...High shifting east and approaching deep
mid- level trough from south central Canada to the northern Plains
will bring strong return flow to the area Monday night into
Tuesday. Mid- level jet and PWAT surging to 1.8 to 2.0 inches
(near the max for early July) will certainly allow for widespread
showers with drenching downpours setting up later Monday night
through at least part of Tuesday, before another round of showers
and maybe a better chance of thunderstorms arrive later Tuesday
into Tuesday night. There are some signals that heaviest rain on
Tuesday night may remain just to our south, but probably too early
for those type of details. If both rounds of moderate to heavy
rain impact similar areas, could have additional impacts in terms
of flooding. WPC continues to highlight majority of our area
within slight risk for excessive rainfall. At this point, does
appear greatest risk for severe storms may remain to our west late
Tuesday into Tuesday night with MUCAPES are well over 1000J/kg.
If sufficient instability makes it into central WI, could be
stronger storms with more than sufficient effective shear progged.

Looking ahead for the period around the holiday, the day before
the 4th looks dry and seasonably warm with highs in the 80s.
Unfortunately, the active pattern does not look to take a holiday
and more rain is expected to move back in later on the 4th and
lasting into Friday. Some timing differences in models, especially
in how quick shower chances return for Thursday afternoon and
Thursday evening. Unsettled weather pattern continues into the
weekend as slow moving low pressure system only slowly exits to
the east. Given that, temperatures will likely be at or even
slightly below normal.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1256 PM CDT Sat Jun 29 2024

A cold front will track across the region late this afternoon into
early this evening. Isolated light showers could occur just about
anywhere as the front crosses, but the greatest chances for
thunder will be over northeast WI, but most likely staying to the
north of GRB and MTW (e.g. Door County). Conditions will be VFR
ahead of the front but will fall to MVFR in its wake over central
and north- central WI. Even after the front moves through, cigs
from the Fox Valley to the lakeshore will only fall to low-end
VFR. Late tonight through Sunday will feature clearing skies and
great flying weather at all terminals.

Gusty northwest winds will develop in the wake of the cold front
passage, especially from late this afternoon through this evening.
Winds will slowly diminish overnight.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA