000
FXUS63 KGRB 241733
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1233 PM CDT Wed Apr 24 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

 - Elevated fire weather conditions are possible Today and
   Thursday due to relative humidities ranging from 15 to 25
   percent. However, relatively light winds and cool temperatures
   will keep conditions from meeting critical fire weather
   thresholds.

 - Two systems will result in rounds of showers and thunderstorms
   late Friday through Sunday night. There is a potential for
   severe storms, though there is still uncertainty on when the
   greatest potential will be. Storms this weekend could also
   produce locally heavy rain with isolated flash flooding
   possible.

&&

.DISCUSSION...
Issued at 328 AM CDT Wed Apr 24 2024

Short Term...Today...Tonight...and Thursday

High pressure over northern Ontario will build across the western
Great Lakes today. Lingering clouds early this morning will quickly
give way to sunny skies after daybreak. Gusty northerly winds will
also diminish while turning more to northeast. Main concern today
and Thursday is fire weather with low humidities expected with the
high pressure overhead.

Temperatures will be below normal today with onshore winds keeping
lakeshore locations chilly mainly around 40. Farther inland mid
50s seem achievable given the sunny skies and deep mixing. We have
not started frost/freeze headlines for any part of our forecast
area yet and it is a good thing, because if we had, we would need
some headlines for tonight with lows at or below freezing across
the board, including readings bottoming out near 20 for much of
the northwoods north of a line from Tomahawk to Wausaukee. High
temperatures on Thursday will bounce back up with another day of
sunny skies and deep mixing. Still cool near the lake with onshore
southeast winds. Leaned on bias corrected MOS guidance inland
which yielded widespread upper 50s to lower 60s.

Long Term...Thursday Night Through Tuesday

An active pattern is taking shape for the weekend as two systems
will impact the areas with rounds of showers and thunderstorms.
For Thursday night, high pressure will continue to move away from
the area while a warm front shifts northward across the central
plains southeast into Tennessee. Easterly winds should be on
the increase Friday into Friday night as the warm front approaches
the state. The forecast already becomes complicated as the
ECMWF/Canadian models are considerably slower with the arrival of
the rain on Friday compared to the much quicker NAM/GFS solution.
The model tendencies are to eject the main system out quicker with
closed 500mb systems, thus will lean toward the ECMWF/Canadian
solution. I have lowered rain chances for the Friday period, and
may need to be trimmed back even more if the ECMWF/Canadian trends
hold true.

On Friday night, the warm front lifts northward. The placement
of the front should keep it mainly south of the area. Showers
will continue to overspread the area with the chances of
thunderstorms from late evening into the overnight. Models were
showing several hundred J/KG of CAPE and 0-6 km shear values of 35
to 45 knots. Could be some stronger storms with hail and gusty
winds as there will be strong winds off the deck later Friday
night. On Saturday, the main question is how far north the warm
front will make it into northern Wisconsin. It is the time of the
year where warm fronts at times struggle to make it as far north
as the models would suggest due to the cooling effects of the
colder waters of the bay and Lake Michigan. With the low tracking
to the northwest of the area, there will be a tendency to push
the warm front too far north across northeast Wisconsin near the
bay/Lake Michigan. This could have a significant impact on high
temperatures and what the real surface based CAPE values will be.

Even if clouds linger, most unstable CAPE values off the models
were in the 1,000 to 2,000 J/KG with 0-6 km shear values around 45
knots. Stronger storms are possible Saturday into Saturday
evening. For Saturday night, the surface boundary will sink
southward due to outflow boundaries and maybe some lake
enhancement of the southward push of the boundary due to the
colder waters from the bay and Lake Michigan. Another round of
showers and thunderstorms are expected at times late Saturday
night and more likely Sunday into Sunday night as the next low
pressure system moves into northern Wisconsin Sunday night. The
chances of rain continue Monday morning across eastern Wisconsin
with the passage of the cold front, while some showers will linger
at times during the day across the north. High pressure will
prevail on Tuesday with dry conditions across the area.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1233 PM CDT Wed Apr 24 2024

Minimal aviation impacts are expected through Thursday as a
Canadian high pressure sinks south over Ontario and delivers a
very dry air mass to the region. This morning`s clouds have
cleared out and skies should remain clear with VFR conditions
through the TAF period. Light 5-10kt winds will be shifting
around from the northeast to east then southeast this afternoon
and evening. Overnight winds become light and variable then
increase to around 10kt out of the southeast Thursday.

&&

.FIRE WEATHER...
Issued at 328 AM CDT Wed Apr 24 2024

Elevated fire weather conditions are possible Today and Thursday
due to a very dry airmass that will move into the region with high
pressure centered over northern Ontario. Afternoon RH values of
15 to 25 percent are likely today, but cooler temps are anticipated
in the lower 40s lakeside to the low to mid 50s inland. Winds
will be light, so conditions will not meet critical fire weather
thresholds.

On Thursday, RH values will be slightly higher between 20 and 30
percent, but temps and winds will both be slightly higher. Even
so, conditions will not meet critical fire weather thresholds.

&&

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

&&

$$

DISCUSSION.....JLA/Eckberg
AVIATION.......GK
FIRE WEATHER...JLA