172
FXUS63 KGRB 250949
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
449 AM CDT Sat May 25 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Memorial Day weekend starts off dry for today, but rain chances
  increase by late Sunday morning and continue into Memorial Day.
  A soaking rain could occur during this time.

- A few rivers over central and eastern Wisconsin could surpass
  minor flood stage early next week.

- Below normal temperatures area expected for the first half of
  next week. Patchy frost is possible Thursday morning over parts
  of northern Wisconsin.

&&

.DISCUSSION...
Issued at 449 AM CDT Sat May 25 2024

Short Term...Today...Tonight...and Sunday

Skies will continue to clear from west to east early this morning
as a ridge of high pressure builds in across the western Great
Lakes region. Mostly sunny skies and breezy conditions are
expected today as winds shift from west to southwest throughout
the day. An isolated shower is possible in north-central Wisconsin
late this afternoon as a weak shortwave rotates around an upper
low located across southern Canada. Highs today are expected to
range from around 70 across the north, to the lower 70s across the
rest of the region away from Lake Michigan.

Surface winds will turn south-southeast tonight as the area will
be in between the departing ridge of high pressure to the east and
a low approaching from the southwest. Despite mostly clear skies,
some modest warm air advection will keep temperature relatively
warm tonight as low temperatures only fall into the lower to
middle 50s.

A surface low tracking through the mid Mississippi Valley with an
attendant mid level negatively tilted trough and PV anomaly
tracking through the southwestern Great Lakes will bring
precipitation back to the area for Sunday. Rain will spread in
across central Wisconsin early Sunday morning, then across the
rest of the area late Sunday morning into early Sunday afternoon.
While this system will bring a slug of significant moisture and
decent dynamics through Wisconsin, instability will be lacking as
MUCAPEs only rise to a few hundred J/kg Sunday afternoon. This
meager instability will mean only isolated thunderstorms are
expected across central and east-central Wisconsin Sunday
afternoon, with the severe threat staying well to our south.
Although PWATs are only expected to be 0.5 to 0.75 inches, the
steady rain for much of the day could add up to 0.5 to 1 inch
during the day on Sunday. Highs on Sunday are only expected to
rise into the 60s with the steady rain showers for much of the
day.

Long Term...Sunday Night Through Friday

A progressive mean flow across the CONUS will bring two more
shortwave troughs through the Great Lakes early next week. This
flow becomes more amplified toward mid-week with upper troughs
over both coasts and an upper ridge over the central CONUS. This
upper ridge should bring dry conditions to northeast WI for the
end of the forecast period. Temperatures will run at or below
normal through mid-week, then warm slightly above normal by late
next week.

Sunday night and Memorial Day...
Showers/thunderstorms to be ongoing at the start of the period as
a mid-level shortwave trough to be moving through the region.
Stronger storms would appear to remain to our south where a
surface low sliding toward southern sections of the Great Lakes
will be accompanied by a cold front. Locally heavy rain is still
possible during the evening as PW values to be 1.25-1.50" and
northeast WI to reside in the right entrance region of the upper
jet. Precipitation should trend down overnight across central WI
as the shortwave trough begins to exit the area. Min temperatures
to be in the middle 40s to lower 50s. The forecast for Memorial
Day remains tenuous as the models are having timing issues between
how fast the initial system departs and the approach of another
shortwave trough in the afternoon. The NAM and CMC are slower with
the exit of the first system, thus there is not much of a break in
the rain chances. Conversely, the GFS and ECMWF are faster with
the exit of system one, thus at least the morning of Memorial Day
would be dry. For now, have kept a minimal pop for the morning
hours and keep chance pops for the afternoon. Max temperatures to
mainly be in the middle to upper 60s (slightly cooler near Lake
MI).

Monday night and Tuesday...
Spotty rain chances would continue into Monday night, but this
shortwave trough is rather weak and with no surface features
evident, any precipitation would be very light. Otherwise, partly
to mostly cloudy skies can be expected with min temperatures to
range from the lower to middle 40s north-central WI, upper 40s to
around 50 degrees east-central WI. Yet another (and stronger)
shortwave trough quickly dives southeast into the Great Lakes on
Tuesday and bring another chance of showers/thunderstorms to
northeast WI. Shear is forecast to be very weak (25 kts or less),
thus severe potential looks to be very low. More clouds and
precipitation chances will temperatures below normal with lower
60s north-central, middle to upper 60s elsewhere.

Tuesday night and Wednesday...
A few showers could linger over east-central WI early Tuesday
evening as the shortwave trough still in the process of exiting
the area. Otherwise, a gradual decrease in clouds are expected for
Tuesday night as high pressure starts to build over the Upper MS
Valley. Mostly sunny skies are forecast on Wednesday as the high
pressure settles over the western Great Lakes. A northerly wind
will keep temperatures a little below normal with readings in the
lower to middle 60s near Lake MI, middle 60s to around 70 degrees
inland.

Wednesday night and Thursday...
Clear skies and nearly calm winds will allow temperatures to
quickly fall Wednesday night, thus may have to watch for potential
frost over northern WI. As the high pressure drifts toward the
eastern Great Lakes on Thursday, winds will shift to the south and
pull warmer air back into WI. Expect max temperatures on Thursday
to be in the middle to upper 60s near Lake MI, lower to middle 70s
inland.

Thursday night and Friday...
As the mean flow becomes more amplified with time, systems to slow
their eastward movement. Therefore, the high pressure to remain
parked over the eastern Great Lakes through Friday and with the
upper ridge overhead, anticipate dry conditions to persist.
Prevailing south-southwest winds will continue to bring warmer air
into northeast WI as max temperatures Friday climb to around 70
degrees lakeside, middle to upper 70s inland.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1005 PM CDT Fri May 24 2024

Showers were tapering off over eastern WI, and scattered showers
were noted along a cold front in NC WI. The threat of storms
should be about over by issuance time, so won`t carry any mention
in the TAFs. MVFR/IFR ceilings will improve from west to east as
the cold front shifts through late this evening into the early
overnight hours, followed by clearing skies (except over far NC
WI).

Winds will become gusty from the west after the frontal passage,
then turn S-SW in the mid to late afternoon on Saturday. A period
of LLWS is expected to impact the northwest half of the forecast
area overnight into early Saturday morning, and also possibly for
a brief period in NC WI Saturday evening.

&&

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

&&

$$

DISCUSSION.....Kurimski/Kallas
AVIATION.......Kieckbusch