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LMZ541 Rock Island Passage To Sturgeon Bay Wi- 556 Pm Cdt Wed Apr 24 2024
Tonight - E wind 5 to 10 kts veering S after midnight. Clear. Waves 2 ft or less. Thursday - S wind 5 to 10 kts. Sunny. Waves 2 ft or less. Thursday night - SE wind 10 to 15 kts. Clear. Waves 2 ft or less. Friday - SE wind 10 to 20 kts. A chance of rain showers in the afternoon. Waves 1 to 3 ft.

LMZ500
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FXUS63 KGRB 250308 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 1008 PM CDT Wed Apr 24 2024

Updated aviation portion for 06Z 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 06Z TAF Issuance Issued at 1005 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 to 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 60 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.

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