Sunrise 5:16 AM   Sunset 8:20 PM Moonrise 5:35 PM   Moonset 3:40 AM

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LMZ542 Sturgeon Bay To Two Rivers Wi-two Rivers To Sheboygan Wi- 327 Am Cdt Mon May 20 2024
Early in the morning - SE wind 5 to 10 kts. Mostly cloudy. Waves 2 ft or less. Today - SE wind 10 to 15 kts. A chance of rain showers in the morning. A chance of Thunderstorms. Light rain showers likely in the afternoon. Waves 1 to 3 ft. Tonight - NW wind 5 to 10 kts. A chance of light showers and Thunderstorms in the evening. Patchy fog. Waves 1 to 3 ft. Tuesday - E wind 10 to 15 kts. Patchy fog in the morning. A chance of rain showers. Waves 2 ft or less. Tuesday night - SE wind 10 to 20 kts veering S 15 to 25 kts after midnight. Gusts to around 30 kts. Rain showers in the evening. A chance of Thunderstorms. A chance of rain showers after midnight. Waves 2 to 4 ft building to 4 to 7 ft. A small craft advisory may be needed.

LMZ500
No data

FXUS63 KGRB 200353 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 1053 PM CDT Sun May 19 2024

Updated aviation portion for 06Z TAF issuance

KEY MESSAGES

- Thunderstorms are possible Monday. An isolated severe thunderstorm could occur during the afternoon south of Highway 29. The main threats will be damaging winds and large hail.

- There is increasing confidence in the potential of a significant severe weather outbreak late Tuesday afternoon into Tuesday evening. Damaging winds, large hail and a few tornadoes are possible. Heavy rainfall and localized flooding is also possible.

DISCUSSION
Issued at 246 PM CDT Sun May 19 2024

Short Term...Tonight and Monday

High pressure ridge that is bringing dry weather this afternoon will give way to low pressure system and approaching warm front late tonight. Wave of low pressure eventually makes it to western Wisconsin on Monday while warm front attempts to lift south to north across Wisconsin.

As low-level jet and elevated instability shifts into western Wisconsin late tonight, swath of showers and some elevated thunder will shift into central Wisconsin late tonight, even more so toward daybreak on Monday. Coverage of these showers will be enhanced by divergence aloft from upper jet across Lake Superior.
On Monday, showers and some thunder will shift west to east through midday riding along the nose of low-level jet. Don't expect any of these storms to be severe, but with 1.25+ inch PWATs moving in there could be heavy downpours. Most areas will see less than 0.50 inch of rain through early afternoon.

There is then loose agreement of a lull behind this initial wave of showers and thunder from the subsidence before additional showers and storms develop as sfc warm front and building instability arrive from the southwest as highs most areas rise into at least the lower 70s and dewpoints push toward the 60 mark.
Appears greatest coverage of the additional convection will stretch from central Wisconsin to east-central Wisconsin. Though MLCAPEs could rise above 1000J/kg, effective shear is weaker mainly 20 kts or less, suggesting pulse type mode to any storms. However, the lack of forecast shear may be offset by convective modulated shortwave that moves through as well mid to late aftn. If that wave is stronger (models differ on the strength), then at least isolated severe storms would be possible over southern portion of the forecast area where SPC currently has a marginal risk. Any storms will have the potential to produce heavy downpours as the PWATs stay in the 1.30 to 1.50 inch range.

Long Term...Monday Night Through Sunday

Thunderstorms trends, including severe and heavy rainfall potential Monday evening and Tuesday afternoon and evening, will be the main forecast concerns.

Depending on the timing of an MCV, there may still be a chance of thunderstorms and a marginal severe threat over the southeast part of the forecast area early Monday evening. This would occur as the SE CWA briefly resides in the warm sector of a weak low pressure system tracking through the area. If the MCV moves through quicker, the severe threat would be confined to the afternoon. Regardless, there does appear to be a lull in the precipitation chances from 03z-12z/Tuesday, along with potential for patchy fog. Lows should be in the upper 40s and 50s.

Confidence is increasing for a potentially significant severe weather event Tuesday late afternoon and evening. A potent low pressure system (990 mb low) is expected to track just west of the forecast area late Tuesday afternoon and evening. Timing of this will be critical, as an earlier arrival would help to maximize instability in the warm sector over the southern part of the forecast area area. Even if the system arrives in the evening, advection of warm/moist air (dew points in the 60s) and steep mid-level lapse rates (7-8 C/km) should support at least a narrow tongue of modest instability into the SW part of the CWA The strength of the dynamics (negatively-tilted short wave trough and low-level convergence with a 50-60 kt LLJ) and shear (0-6 km shear of 50-60 kts, and 0-3 km helicities of 400-800) should help overcome limited instability and bring a round of impactful severe weather to the region. Supercells with damaging winds, large hail and a few tornadoes will be possible. Given the dynamics and anomalously moist air mass, heavy rainfall and localized flooding will also be a concern, especially in any areas that received heavy rainfall with earlier rounds of convection.

Wrap-around showers to persist over the northwest part of the forecast area on Wednesday, followed by mainly dry conditions Wednesday night through Thursday night. A cold frontal passage will bring the next significant chance of rain later Friday into Saturday, but timing issues are evident.

AVIATION
for 06Z TAF Issuance Issued at 1053 PM CDT Sun May 19 2024

VFR conditions will continue late this evening and most of tonight with mainly mid and high clouds spreading across the area.
A few sprinkles or light showers are are possible, but will have no impacts to flying conditions.

An area of showers will arrive from southwest to northeast after 08z ahead of an approaching low pressure system and frontal boundary, continuing at times into Monday morning. Weak instability could allow for a few embedded thunderstorms. A break is expected for much of the late morning and afternoon, with additional showers and storms developing later in the day as the warm front lifts across the area, especially across eastern WI, with more spotty activity further west. Still some uncertainty just how long the break will be and where the second round of activity will be focused. VFR conditions look to last through at least 11z then MVFR and possibly some IFR conditions are expected at times on Monday, associated with the heavier showers and stronger storms. The strongest storms could produce gusty/erratic winds, hail and heavy rain. Tried to limit the thunder/ceilings/ visibilities conditions as best as possible to 2-3 hour windows where the threat looks to be greatest, but those may need to be shifted/changed as models hone in on exact timing of each round of showers/storms. Another round of showers and storms looks to arrive late Monday night (after 06z).

Fog may develop on Lake Michigan Monday into Monday night as dewpoints climb ahead of the low, but should stay mainly over the lake, so will not include at MTW. In addition, some fog will be possible across most land areas Monday night as winds die off and recent rain will provide moist low levels, but winds just off the surface and cloud cover may limit this threat.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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