Sunrise 5:41 AM   Sunset 7:57 PM Moonrise 2:06 AM   Moonset 10:33 AM

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LMZ541 Rock Island Passage To Sturgeon Bay Wi- 142 Pm Cdt Tue Apr 30 2024
This afternoon - SW wind 10 to 15 kts. Mostly cloudy. Waves 2 ft or less. Tonight - S wind 10 to 15 kts. A slight chance of rain showers in the evening, then rain showers and a slight chance of Thunderstorms after midnight. Waves 2 ft or less building to 2 to 4 ft early in the morning. Wednesday - SW wind 10 to 20 kts veering W in the afternoon. Gusts to around 25 kts. Partly cloudy. Waves 2 to 4 ft subsiding to 1 to 3 ft late in the afternoon. A small craft advisory may be needed. Wednesday night - NW wind 10 to 15 kts. Partly cloudy in the evening then becoming mostly cloudy. Waves 2 ft or less.

LMZ500
No data

FXUS63 KGRB 301923 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 223 PM CDT Tue Apr 30 2024

Forecast discussion for routine afternoon forecast issuance

KEY MESSAGES

- A low pressure system will bring a period of showers and embedded storms from late this evening into the overnight hours tonight. No severe weather is expected, but a few storms could bring brief gusty winds and small hail. Another round of showers and storms are likely from Thursday into Friday.

- Gusty west winds from 30 to 40 mph are expected over central and east-central Wisconsin on Wednesday. While recent rains will limit the fire weather potential, the gusty winds will bring a threat of isolated power line fires.

- Due to recent and upcoming rainfall, rivers and streams will be on the rise late this week. Some rivers are forecast to reach bankfull stage by Friday or Saturday.

DISCUSSION
Issued at 223 PM CDT Tue Apr 30 2024

Short Term...Tonight and Wednesday

The latest RAP analysis and satellite/radar imagery show widespread low stratus across north-central to far northeast Wisconsin within a shallow, cool airmass. The back edge of this cloud cover has been slowly shifting to the northeast as return flow on the western flank of a ridge axis increases over the northern Mississippi Valley. Looking upstream, an elongated area of low pressure exists to the lee of the Rockies ahead of a potent shortwave trough. Showers and thunderstorms have developed on the leading edge of the moisture axis in a region of elevated moisture convergence from eastern South Dakota to Iowa. As low pressure tracks northeast across the region, precip and thunderstorm trends along with gusty winds on the backside of the system are the main forecasts concerns through Wednesday afternoon.

Showers and thunderstorm potential: Low pressure will be intensifying as it moves from southern Minnesota early this evening to western Lake Superior by Wednesday morning. Strong QG forcing will be passing across the northwest half of Wisconsin as the low passes to go along with steep mid-level lapse rates upwards of 7 C/km.

This forcing combined with a 40-50 kt low level jet will lead to a swath of showers and embedded thunderstorms lifting from southwest to northeast across the region from late evening through the overnight hours. The HRRR indicates that elevated instability will weaken though the night, but can reach 500-750 j/kg as storms enter central WI late this evening. As a result, a few strong storms will be possible, primarily over central WI, but no severe weather is expected. The storms will become more isolated over north- central and far northeast WI late tonight as instability wanes. There is a 30-40% chance of 0.50" or more of rainfall over parts of central to north-central WI tonight.

Gusty winds Wednesday: As the low lifts across Lake Superior, boundary layer winds will increase in a cold advection regime on Wednesday morning. HRRR/RAP/GFS all point to substantial low level moisture beneath the inversion and within a broad thermal troughing regime. As a result, some drizzle may stick around into Wednesday morning over far northern WI. The cloud cover and light precip will likely hinder wind gust potential across the region.
Forecast soundings and NBM probabilities indicate the greatest potential for wind gusts above 35 mph will occur over east-central WI (40-60%) in the 1-2 pm hour, but those probabilities fall to under 20% for wind gusts greater than 40 mph. Therefore, while it will be windy, gusts do not appear strong enough for a wind advisory at this time.

The gusty winds of 30-40 mph could lead to isolated power line fires, but recent rainfall and potential for underperforming winds due to cloud cover should limit the potential substantially. Think the potential is greatest over central WI to far northeast WI where green up has yet to occur in the sandy soil/forested areas.

Long Term...Wednesday Night Through Tuesday

An active pattern containing several systems and multiple rounds of precip is set to persist through the extended. Main focus will be on an end of week system that will bring rain chances to the western Great Lakes starting Thursday afternoon. As a result, the majority of the forecast area is under a slight risk for excessive rainfall Thursday through Friday. Expect river/stream levels to be on the rise through the end of the week, with some locations reaching bankfull by the end of the week.

Thursday/Friday precip chances... Rain chances will begin to ramp up toward the latter half of the week as a robust trough spins up a lee cyclone that will eject into the upper Midwest by Friday morning. Warm air advection precip will likely arrive Thursday afternoon out ahead of a warm front before becoming more widespread Thursday evening along a trailing cold front as it moves east across the forecast area. Models are still struggling to hone in on QPF amounts, although ensemble guidance currently shows a strong signal for at least half an inch of storm total QPF through Friday. Given strong poleward moisture transport and an open Gulf, some models (GFS and ECMWF) would suggest closer to 0.75 to 1" of event QPF. Most convective elements look to remain to our south and east, although an elevated thunderstorm with some gusty winds cannot be ruled out Thursday evening through Friday morning with MUCAPE values in the 300 to 400 J/kg range (NAM). Best chances for thunder currently look to be in east- central Wisconsin, although any storms will have to overcome a robust surface inversion due to easterly flow advecting a stable lake airmass onshore. Drier conditions will then arrive behind the cold front on Friday as winds increase and veer to westerly. Gusts between 20 and 30 mph will be possible during this time, mainly in central Wisconsin.

Saturday/Sunday precip chances... As Friday's surface low continues to decay and exits to the north, another upper-level disturbance is progged to develop in its wake, bringing additional precip chances through the weekend. However, there is still model disagreement about the timing of this feature this far out in the forecast period, and thus how fast precip chances will arrive. Overall QPF amounts look to be lower than the previous system as most of the prime Gulf moisture struggles to make it up into the forecast area. Convective elements currently don't look too impressive, although this may change as additional models come in range.

AVIATION
for 18Z TAF Issuance Issued at 1237 PM CDT Tue Apr 30 2024

In a shallow, cool airmass, MVFR and low VFR stratus continues to blanket much of northern Wisconsin. Drizzle has been observed at times as well. The back edge of this cloud mass will continue to shift northeast this afternoon as ceilings gradually rise with the heat of the day. The clearing may not reach north-central WI until later this afternoon.

While a brief period of clearing will occur this afternoon, clouds will quickly return as a low pressure system approaches the region this evening. This low will bring a period of showers and thunderstorms to the region late this evening into overnight.
Ceilings and visibilities are forecast to fall to IFR/MVFR over central and north-central WI when the heavier showers move through.

After the rain ends, low ceilings in the IFR/MVFR range will likely persist through much of Wednesday morning. Some improvement to ceilings are likely over east-central WI where the dry slot will be present. If this occurs, west-southwest wind gusts will increase to 30-35 kts over east-central WI by late morning.

Lastly, the strong system will bring a period of low level wind shear to the taf sites late tonight into Wednesday morning.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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