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LMZ522 Expires:202406030200;;323942 Fzus53 Kgrb 021815 Nshgrb
nearshore marine forecast national weather service green bay wi 115 pm cdt Sun jun 2 2024
for waters within five nautical miles of the shore on lake michigan
lmz521-522-030200- green bay south of line from cedar river to rock island passage and north of a line from oconto wi to little sturgeon bay wi- green bay south of line from oconto wi to little sturgeon bay wi- 115 pm cdt Sun jun 2 2024
This afternoon - SE wind 5 to 10 kts. Mostly Sunny. Waves 2 ft or less. Tonight - SE wind 5 to 10 kts. Partly cloudy. Waves 2 ft or less. Monday - SE wind 10 to 20 kts. A chance of rain showers in the morning, then rain showers likely in the afternoon. Waves 2 ft or less. Monday night - SE wind 5 to 10 kts. A chance of rain showers. Waves 2 ft or less.

LMZ500
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FXUS63 KGRB 021916 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 216 PM CDT Sun Jun 2 2024

Forecast discussion for routine afternoon forecast issuance

KEY MESSAGES

- Showers are likely with a chance of thunderstorms on Monday.
There is a marginal risk of severe thunderstorms over parts of east-central Wisconsin in the afternoon. Gusty winds, small hail and brief heavy rain would be the main threats.

- More strong storms are possible Tuesday afternoon into Tuesday night. Gusty winds, small hail, and heavy rain will be the primary hazards.

- Conditions hazardous to small craft will be possible at times from Wednesday through Saturday.

DISCUSSION
Issued at 216 PM CDT Sun Jun 2 2024

Short Term...Tonight and Monday

Main forecast challenge to be timing/extent of showers and thunderstorms on Monday with the small possibility of stronger storms in the afternoon.

The 19Z MSAS surface analysis showed high pressure that extended from northern Lake Superior to the mid-MS Valley. An area of low pressure was situated over central SD with a warm front that stretched southwest into southwest IA. Visible satellite showed high clouds streaming over WI with fair weather cu that had developed in the heating of the day.

A mid-level shortwave trough will move across the northern Plains into the Upper MS Valley tonight. Clouds are expected to steadily be on the increase through the night as south winds pull moisture northward. This moisture transport, coupled with increasing isentropic lift, will bring a chance of showers/thunderstorms into north-central and central WI toward daybreak. There could be some patchy fog to develop near Lake MI as moist air moves over the cooler lake waters. Min temperatures tonight to range from the lower 50s near Lake MI, to the upper 50s across north-central/ central WI.

The shortwave trough sweeps into the western Great Lakes on Monday and bring showers/chance of thunderstorms to all of northeast WI.
The precipitation will begin to diminish in the afternoon across central WI as the better forcing shifts east with the trough. Some of these storms will have the capability of becoming strong as shear reaches 30-40 knots in the afternoon, especially over east- central WI. Models indicate MUCAPES of 500-1500 J/KG, but much of this instability will depend on how fast showers/storms move east.
Latest guidance from SPC has moved parts of east-central WI into the marginal risk for severe thunderstorms based on some models developing a weak low pressure on the backside of the shortwave trough. Gusty winds and small hail would be the main threats.
Another factor to watch will be for locally heavy rains as PW values climb to around 1.5 inches and the forecast area to be under the favorable right entrance region of the upper jet for lift. Max temperatures Monday to be in the middle 60s near Lake MI, lower to middle 70s inland.

Long Term...Monday Night Through Sunday

An energetic weather pattern will bring periods of showers and storms from Monday night through Wednesday thanks to southwest flow aloft and occasional shortwave energy traversing the region.
Thunderstorm chances and potential impacts are the primary forecast concerns during this period.

Thunderstorm Chances: Shortwave energy will be exiting the region by the start of Monday evening. Modest elevated instability will remain in place behind the shortwave, but large scale ascent will depart with the wave and nocturnal stabilization should lead to only low chances of showers and storms. Most models generate light qpf over far northeast Wisconsin and this looks appropriate.

Northern WI will be in a weak warm advection pattern for the rest of the night into Tuesday morning. Relatively steeper mid-level lapse rates near 7 C/km will remain over southern WI and northern IL during this time and a relative lull in forcing should occur. Will likely see a break in the precip coverage during this time.

This may change on Tuesday afternoon if shortwave energy arrives from the southwest and gets to interact with daytime instability.
Not all guidance shows this shortwave moving into northern WI, so confidence is relatively low with the details. But if it does, dewpoints will be creeping up into the middle and upper 60s by this time and modified forecast soundings indicate instability upwards of 2000 j/kg. With temps approaching their convective temps by midday, conditions support scattered thunderstorms developing through the afternoon. Localized heavy rain will be possible given the relatively slow storm movement.

Additional thunderstorms are likely to arrive from the west during the evening when a potent shortwave and associated cold front move through the region. Forcing looks robust for widespread precipitation, but instability will be at its diurnal minimum so thunderstorm chances will be waning through the night. Better chance of strong thunderstorms will reside west of the region.

The region will reside under upper troughing on Wednesday. Models depict weak instability developing with the heat of the day that could lead to scattered storm development in the afternoon. Far northern WI will have the highest chances.

Severe Potential: The main period to watch will be Tuesday afternoon into Tuesday night. As mentioned above, ample instability (2000 j/kg cape) will be in place as dewpoints climb into the mid and upper 60s. However, deep layer shear is weak and roughly around 20 kts. Seems like a recipe for pulse storms and perhaps an isolated severe threat given the magnitude of instability and dcapes around 700 j/kg. Outflow boundaries and lake breezes could also augment the forcing arriving aloft (if it does arrive). Strong winds and hail will be the primary threats.

Prospects for severe storms on Tuesday night look low as timing of the front coincides with minimal cape of 200-400 j/kg. While deep layer shear will be increasing aloft, storms are likely to be elevated, thereby reducing the severe risk.

Rest of the forecast: Beneath upper troughing, showers look possible on Thursday and Friday. There will be a cooler airmass in place by this time, so thunderstorm potential looks low. Flattened troughing looks to hang around through next weekend which will keep temperatures near to slightly below normal.

AVIATION
for 18Z TAF Issuance Issued at 1226 PM CDT Sun Jun 2 2024

Excellent flying conditions expected this afternoon into this evening with weak high pressure overhead. Anticipate scattered fair weather cumulus clouds and high clouds with 10+ visibility.

Conditions gradually deteriorate late tonight into Monday morning as the high pressure shifts east and a mid-level shortwave trough approaches from the west. The result will see showers/chance of thunderstorms reach central WI toward daybreak with both cigs and vsbys lowering to MVFR.

Conditions deteriorate to MVFR (local IFR) from west to east across the rest of northeast WI on Monday as showers and some thunderstorms spread across the area. While MVFR conditions to prevail, possibility of some IFR conditions exists under any of the heavier showers or storms. In fact, a few storms may become strong Monday afternoon over parts of east-central WI. South winds on Monday could gust to around 20 knots.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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