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000
FXUS63 KGRB 242258
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
558 PM CDT Wed Apr 24 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

 - Elevated fire weather conditions are expected on Thursday due
   to relative humidities ranging from 20 to 30 percent. However,
   relatively light winds and seasonal temperatures will keep
   conditions from meeting critical fire weather thresholds.

 - Two systems will result in rounds of showers and thunderstorms
   from Friday through Sunday night. The latest indications
   suggest a risk of severe storms may develop on Saturday
   afternoon and evening, though confidence is relatively low.
   Storms this weekend could also produce locally heavy rain with
   isolated flash flooding possible.

 - Conditions hazardous to small craft will be possible at times
   from Friday through the weekend on the Bay and Lake.

&&

.DISCUSSION...
Issued at 225 PM CDT Wed Apr 24 2024

Short Term...Tonight and Thursday

A Hudson Bay high pressure system sinking south across Ontario
will bring dry and calm conditions across the region for the rest
of today through Thursday. Clear skies overnight will allow
temperatures to fall into the upper 20s to low 30s across most the
region. While Frost and Freeze headlines are not yet being issued
for central and northeast WI those who got an early start to the
growing season may want cover outdoor plants or bring potted plans
indoors, particular for areas northeast of a Crivitz to Eagle
River line where low temperatures could bottom out near 20
degrees.

Near to slightly above normal temperatures are expected with
deeper mixing and sunny skies Thursday brings highs in the mid
50s to around 60 degrees except along the lakeshore where a 10-
15 mph breezy will limit temperatures to around 50 degrees. With
the dry air mass in place the elevated fire weather concerns due
to low RHs continue through Thursday.

Long Term...Thursday Night Through Wednesday

Focus of this forecast revolves around the heavy rainfall and severe
weather potential from Friday through Monday.

Precipitation and Severe Potential...The first Rocky Mountain
cyclone will be lifting northeast from the central Plains to the
northern Mississippi Valley during the Friday through Saturday night
time frame. Ahead of the cyclone, very dry air will remain in place
on Friday morning and timing of precipitation may be slowed until
late afternoon or evening. However, increasing deep layer ascent via
isentropic lift within a 40-50 kt low level jet will overwhelm the
dry air and lead to a swath of precip spreading from southwest to
northeast across the area on Friday night.  While instability will
be increasing through the night, skinny cape with around 100 j/kg of
cin in the max cape layer will likely limit the severe threat.
Precip amounts in the half to three quarters inch range will be
possible by 7 am Saturday.

Low pressure will be tracking across far northwest Wisconsin on
Saturday with a warm front lifting north of the Upper Peninsula
border in the afternoon.  The low will leave a trailing cold front
behind across north-central to western Wisconsin, which would place
northeast Wisconsin in the warm sector.  Severe parameters become
rather impressive on Saturday afternoon over northeast Wisconsin
assuming cloud cover and precipitation do not slow the heating
curve. Deep layer shear of 30-45 kts and instability of 1000-2000
j/kg would suggest organized severe weather will be possible.  Most
likely looking at a damaging wind and large hail threat, but a
tornado threat may develop depending on how surface heating and low
level wind fields evolve. The greatest threat would occur during
peak heating - mid to late afternoon.

The front is forecast to remain nearby to northeast Wisconsin on
Saturday night.  The severe weather potential looks to diminish as
the atmosphere gets worked over and large scale forcing decreases
for a time.

A second cyclone will then move across the region during the Sunday
and Sunday night time frame.  Instability does not look as robust as
compared to the previous cyclone, but a severe threat may yet
develop depending on the details.  Heavy rainfall and flooding will
also be a threat by this point as soils will get preconditioned by
rainfall over the previous 1-2 days.  Some light showers may linger
into Monday, but most precip (1-3 inches) will likely fall during
the Friday-Sunday night time frame.

Temperatures...Warm temps in the low to middle 70s are possible on
Saturday if the region can move into the warm sector as expected.
After a brief cool down early next week, temps look to warm up again
by the middle of next week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 555 PM CDT Wed Apr 24 2024

Dry Canadian high pressure will bring VFR conditions to the
forecast area through the TAF period, with only some high clouds
moving through overnight. Light and variable winds will become
SE-S and increase around 10 knots on Thursday.

&&

.FIRE WEATHER...
Issued at 225 PM CDT Wed Apr 24 2024

The elevated fire weather concerns continue through Thursday as
relative humidity values are expected to drop into the 20-
30 percent range and fuel moisture remains fairly low. Concerns
are somewhat tempered with temperatures only forecast to warm
into the mid 50s to around 60s and southeast winds only
increasing to around 10-15 mph Thursday afternoon. Conditions
will not meet critical fire weather thresholds.

&&

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

&&

$$

DISCUSSION.....GK/MPC
AVIATION.......Kieckbusch
FIRE WEATHER...GK