733
FXUS63 KGRB 041958
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
258 PM CDT Sat May 4 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A few strong storms are still possible into early this evening
  across east-central Wisconsin from Appleton to Kewaunee on
  southward.

- Dense marine fog on Lake Michigan will lift this evening as a
  cold front brings cooler and drier air into the region.

- A few rivers will remain around bankfull into next week.

&&

.DISCUSSION...
Issued at 258 PM CDT Sat May 4 2024

Short Term...Tonight and Sunday

Thunderstorms from earlier this afternoon across portions of
central and north-central Wisconsin weakened into a cluster of
showers as it moved into far north-central and northeast Wisconsin.
Dense fog continued on the nearshore waters of Lake Michigan and
across portions of the central Bay of Green Bay from Sister Bay to
Gills Rock. The dense fog did extend inland for a mile or two at
times. Temperatures at 2 pm ranged from the upper 40s at the Lake
Michigan shoreline to the lower 70s from Green Bay southward to
Oshkosh.

For the rest of the afternoon into early this evening, there is
still the potential for stronger storms across portions of east-
central Wisconsin which was still in the warm sector ahead of the
cold front. Latest mesoanalysis indicated surface based/most
unstable CAPE values of 200 to 400 J/KG which is expected to
increase to around 500 to 600 J/KG late this afternoon. 0-6km
shear values near 50 knots combined with wet-bulb zero heights
around nine thousand feet allow confidence in for some stronger
storms to form. Latest satellite images also indicated some
clearing across Waushara and Waupaca counties which should
move into portions of the Fox Valley for the rest of the
afternoon to allow for things to become a little more unstable
this afternoon. Any showers or storms should end around mid-
evening. On the lakeshore, dense marine fog is expected to
continue into the evening until the cold front shifts the winds
to the northwest and advects in cooler and drier air.

Late tonight, patchy fog is possible across portions of central
and north-central Wisconsin. Lows tonight should drop into the
middle 30s to lower 40s. On Sunday, skies will start out Sunday
with clouds on the increase as fair weather cumulus are expected
during the late morning and afternoon. Highs will be in the 60s
to around 70.

Long Term...Sunday Night Through Saturday

High pressure will bring dry weather Sunday night into Monday
evening. Temps may drop into the mid 30s Sunday night but frost
potential looks limited to only the far north where frost/freeze
headlines have not started yet. Monday will feature temps well
into the 60s if not lower 70s. Min RH values look to drop to
around 30 percent, but for most part elevated fire conditions are
not expected as winds will stay mainly less than 10 mph with
gusts to 20 mph at the highest. Any fire weather concerns will be
greatest across the sandy soil regions of northern and central WI
where green up has not fully occurred yet.

The remainder of next week will be dominated by an initially well
organized and rather deep cyclone moving into the northern Plains
Monday night into Tuesday with a warm front extending into the
western Great Lakes. Models seem to be trending slower with
arrival of showers and some embedded thunder on Monday night.
Possible that areas from the Fox Valley to the lakeshore stay dry
through late Monday night. Eventually though, all areas will see
showers and some thunder into Tuesday as surge of deeper moisture
with PWAT values around 1.2-1.3" arrives. Though details are
uncertain, an additional round of showers and thunderstorms could
develop later Tuesday afternoon. Stronger jet energy and ribbon of
instability may reside just south of our area. This likely will hold
the key for whether we`ll see any severe storms on Tuesday. In
terms of rainfall amounts the long term grand ensemble (GEFS, EPS,
and GEPS) show a 50-70% for over 0.5" of QPF late Monday night
through Tuesday night, but are mainly less than 30% for seeing
over 1".

Periods of showers and storms are expected Wednesday through
Friday as the aforementioned cyclone slowly shifts east and
weakens. The disorganized nature of this weakening system makes
specific forecast details difficult to pin down. For now expect
lots of clouds and periods of rain along with a few storms
through the second half of next week. With the recent and
forecast rainfall, many area rivers and streams will likely
continue near or at bank full through next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1226 PM CDT Sat May 4 2024

A band of showers and thunderstorms was moving across central into
northeast Wisconsin early this afternoon. Some of the stronger
storms could produce wind gusts up to 30 knots and pea size hail.
Meanwhile, dense fog was moving northward along the Lake Michigan
coastline and will impact KMTW and all the airport sites in Door
County due to low visibilities or low CIGS. Another cluster of
stronger storms are possible after 21z across east-central
Wisconsin, mainly south of Appleton. Some of these storms could
produce wind gusts to around 40 knots and hail up to one inch
in diameter. MVFR CIGS are expected for a period of time behind
the cold front followed by improving CIGS during the evening.
Some patchy fog is possible late tonight across central and
north-central Wisconsin where skies clear the longer and winds
become fairly light towards sunrise on Sunday.

&&

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

&&

$$

DISCUSSION.....Eckberg/JLA
AVIATION.......Eckberg