832
FXUS63 KGRB 300845
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
345 AM CDT Tue Apr 30 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Active weather pattern to bring a round of showers and embedded
  storms this evening into early Wednesday, with widespread rain
  and a few thunderstorm possible late Wednesday night through
  Friday.

- Gusty west winds up to 40 mph expected on Wednesday. While
  recent rains will limit fire weather concerns, the gusty winds
  will bring a threat of sporadic power line fires.

- Due to recent/upcoming rainfall, rivers and streams will be on
  the rise this week, with some reaching bankfull stage.

&&

.DISCUSSION...
Issued at 343 AM CDT Tue Apr 30 2024

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

Today...plenty of clouds are expected to start the day as low
pressure slowly lifts north/east away from the region. A few
sprinkles, pockets of drizzle and/or light fog will lingering
into the morning hours, especially across northern WI. Look for
decreasing clouds from south to north through the late morning and
afternoon hours as drier air briefly works in, but additional
clouds will spread in from the west later in the afternoon as
the next system approaches. West winds will generally be in the
10-20 mph range through the early afternoon, then will decrease
and shift to the south/southeast. Highs will climb into the upper
50s and 60s for most locations, with a 70 possible in the SW CWA
and slightly cooler readings near the shores of Lake Michigan.

Tonight...the brief break in clouds (and rain) will end quickly
this evening as the next in a series of low pressure systems and
shortwaves cross the Great Lakes. Showers with some embedded
storms are expected to spread west to east across the area,
reaching central WI between 00-03z and 04-07z over eastern WI.
The activity looks to exit by 12z Wednesday. Surface-based
instability is forecast to stay just to our south, but MUCAPEs do
climb to around 700 J/kg, highest across central WI in the mid-
evening. While severe weather is not expected, as the LLJ brings
40+ kt winds aloft, some gusty winds could accompany any of the
showers or storms, along with some small hail as wet-bulb heights
will be on the low side. Models in general agreement bringing
between 0.40-0.75" of rain across much of central and north
central WI, with locally higher amounts over an inch are possible
if/where any storms track over the same location (PWATs around one
inch). Lower amounts under 0.25" in the Fox Valley and lake
shore. Lows will be in the 40s to low 50s.

Wednesday...lingering clouds and possibly some light showers or
sprinkles are expected early in the day, with a period of partly
to mostly sunny skies for most locations by mid-late morning.
Additional clouds are expected later in the day. West winds will
gust to 40 mph as the pressure gradient will remain tight behind
the departing low and good mixing will bring down the stronger
winds. Highs look to range from the 60s across north-central WI
to the upper 60s to lower 70s over eastern WI where some
downsloping should help offset any CAA.

Afternoon relative humidity readings should drop into the 30s
across most locations, lowest in the sandy soil regions where some
upper 20s are possible. Recent/expected rainfall, along with the
continued green-up, will limit overall fire weather concerns;
however, the gusty winds will bring a threat of sporadic power
line fires. And with pine fuels at/near their seasonal peak, could
have some issues if any fires are able to start.

Long Term...Wednesday Night Through Monday

The potential for areal flooding will be the main impact during
the extended period as several chances for showers and storms are
forecast for the latter half of this week and this weekend.
Several area rivers are already on the rise with this weekend
rainfall.

First chance for precipitation is progged to arrive Wednesday
night as a deepening through developing over the Northern Rockies
pulls a lee side cyclone northeast into the upper Mississippi
Valley. Rain shower are expected to become widespread Thursday
with the heaviest rain Thursday afternoon and evening as a right
rear jet quad and mid- level PV anomaly move over the region
along with enhanced poleward moisture transport resulting in PWAT
values of 1-1.5". Event total QPF is expected to range from
around 0.5-1" with locally higher totals possible where the
heavier showers develop. There is a small chance for isolated
embedded thunderstorms Thursday afternoon through early Friday
morning, mainly along a warn front forecast to set up across
central and east-central WI. The threat for any storms that do
develop becoming severe looks low giver MUCAPE values peaking
around 200-400 J/kg and effective shear values around 10-20kt.
Caveat here is if the warm front sets up further north allowing
the warm sector to pusher further north a few stronger storms may
be possible Thursday evening. Showers and a few weak storms may
linger into Friday morning as a cold front pushes through through
the region. Expect dry and breezy conditions behind the front with
westerly wind gusts reaching 20-30 mph at times, highest in
central WI.

Ensemble guidance is showing a second disturbance developing in
the wake of the departing main vertically stacked low. The timing
of this feature remains uncertain as some ensemble members have
it arriving as early as Saturday afternoon while some keep the
region dry until Sunday morning. Current guidance is not showing
much in the way of convective potential with this system, however
given the days 5 and 6 time frame that could change with later
forecasts.

Temperatures are forecast to remain steadily a few degrees warmer
that normal through the extended period with highs each day
ranging form the mid 50s to around 70 degrees. Low temperatures
are expected to fall into the upper 30s to around 50 degrees each
night. Frost/Freeze headlines will be issued as needed beginning
May 1st for central and east-central WI and May 7th for northern
WI.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1044 PM CDT Mon Apr 29 2024

Low pressure moving slowly across Lake Superior will keep cloudy
skies across the area overnight. MVFR ceilings are likely west of
a ESC to DLL line, with IFR ceilings at times northwest of an IMT
to RRL line. VFR ceilings are expected across eastern Wisconsin.

MVFR ceilings are likely over all of the area Tuesday morning,
with rapid clearing from south to north during the afternoon. VFR
conditions are expected Tuesday evening, but showers and scattered
thunderstorms and lower flight conditions are likely later Tuesday
night as another low pressure system approaches from the Plains
states.

&&

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

&&

$$

DISCUSSION.....Bersch/GK
AVIATION.......RDM