606
FXUS63 KGRB 281118
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
618 AM CDT Tue May 28 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Another round of showers and thunderstorms are expected late
  this morning into this evening. Severe weather is not expected,
  but small hail could occur in the stronger storms.

- Due to recent rainfall, a few rivers are expected to remain at
  bankfull but below minor flooding.

- Areas of patchy frost are possible late Wednesday night into
  Thursday morning across far northern Wisconsin.

&&

.DISCUSSION...
Issued at 305 AM CDT Tue May 28 2024

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

Shower and thunderstorm strength and extent into this evening is
primary focus.

Broad troughing aloft is present from Hudson Bay to the Great
Lakes to start off the day. Embedded sharper shortwaves within the
trough continue to drive the show in terms of coverage of showers
and thunderstorms. Wave that brought the showers and storms to end
the Memorial Day holiday weekend on Monday is dropping across the
central Great Lakes, though a few lingering showers remain over
east-central WI. These will diminish before daybreak.

Another batch of lighter showers is slowly rotating across
western Lake Superior and western Upper Michigan ahead of what
appears to be the last sharp shortwave that will bring another
round of scattered showers and thunderstorms to the region later
today. A few showers or sprinkles will drift across northern
WI this morning, but most locations will see likely chances for
showers and some thunder this afternoon into early this evening as
the wave drops across the region and interacts with peak heating
of the day. Effective shear is weaker at 25 kts or less so not
expecting severe storms. However, with lower wbzero heights (5-7kft)
and steeper mid-level lapse rates, small hail could occur in just
about any stronger shower or storm this afternoon. Forecast
soundings are fairly moist and sfc-delta theta-e values look
unfavorable, so strong wind gusts appear unlikely. But, could see
wind gusts to 40 mph where 0-3km lapse rates are highest in the
far south and southeast part of the forecast area. High temps
today will still be a bit below normal with readings only as warm
as the upper 60s in the far southern part of the area. Normal
highs are in the lower 70s. Tonight, chances for showers and a
rumble of thunder will linger through late evening, then slowly
fade after midnight as the shortwave will still be in the vcnty.
Clouds will diminish late, but given amount of clouds upstream
this morning over Ontario, bumped up cloud cover some over north-
central WI late tonight when most guidance tries to clear things
out completely. Lows will depend on extent of cloud cover. Stuck
toward continuity for now with upper 30s far north and upper 40s
southeast.

Wednesday will be dry but feature decent coverage of fair weather
cu blossoming late morning into the afternoon especially central
WI. Highs will still be a touch below normal, but should reach
the upper 60s most locations. Locations along Lake Michigan will
remain around 60 into the lower 60s with northerly flow in wake
of the system that moves through later today and to the south and
east of high pressure building in from Ontario to the Upper
Mississippi river valley.

Long Term...Wednesday Night Through Monday

The extended will see a longer period of dry conditions arrive
from the middle to end of the work week. The next chance for some
more widespread rainfall and storms will arrive next weekend.

Wednesday night through Friday...A high amplitude ridge will be
working its way across the region at the beginning of the extended
Wednesday. Temperatures under the ridge will be fairly cool,
especially Wednesday night when clear skies, light winds, and a
dry air mass may bring a window for frost to northern Wisconsin.
Winds will gradually turn south to southwesterly again Thursday
and Friday, which will bring back some warmer air and Gulf
moisture for the weekend. Included some low pops for late Friday
if the upper ridge moves out more quickly than expected, but most
locations, especially those in eastern WI, should still see a dry
day for Friday.

Rest of the forecast...The return of more southwesterly flow will
bring moisture back to the region for the weekend. As a result,
models also bring back the active weather. As of this forecast
cycle, Saturday and Sunday show two rounds of active weather, the
first with a round of warm air advection as a shortwave pushes
south of the area and then the second as another weak cold front
follows on Sunday. Timing on this precipitation remains variable,
but would expect interim dry periods for any one location between
rainfall. Depending on the timing of the rain, Sunday also will
see a chance to get highs into the lower to middle 80s across the
area.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 616 AM CDT Tue May 28 2024

A few showers will be around through mid morning, then showers and
some thunderstorms will blossom midday through the afternoon as a
stronger system crosses the area. The greatest chance for storms
will occur over the southwest half this afternoon. Continued to
carry a TEMPO group to cover the storms at AUW/CWA/ATW/GRB. In
general even with the showers and thunderstorms, VFR conditions
are expected to prevail. However, brief MVFR conditions will
accompany any storms. Lingering showers and storms will end by
late evening over central Wisconsin and during the overnight hours
across east-central Wisconsin.

&&

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

&&

$$

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