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LMZ543 Expires:202405050200;;619318 Fzus53 Kgrb 041829 Nshgrb
nearshore marine forecast national weather service green bay wi 129 pm cdt Sat may 4 2024
for waters within five nautical miles of the shore on lake michigan
lmz542-543-050200- sturgeon bay to two rivers wi-two rivers to sheboygan wi- 129 pm cdt Sat may 4 2024
.dense fog advisory in effect until 11 pm cdt this evening - .
This afternoon - S wind 5 to 10 kts. Widespread dense fog. A slight chance of light showers and Thunderstorms. Waves 2 ft or less. Tonight - W wind 5 to 10 kts veering nw 10 to 15 kts after midnight. Widespread dense fog in the evening. Rain showers likely and a chance of Thunderstorms in the evening. Waves 2 ft or less. Sunday - NW wind 5 to 10 kts veering se in the afternoon. Mostly Sunny. Waves 2 ft or less. Sunday night - SE wind 5 to 10 kts. Clear. Waves 2 ft or less.

LMZ500
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FXUS63 KGRB 041731 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 1231 PM CDT Sat May 4 2024

Updated aviation portion for 18Z TAF issuance

KEY MESSAGES

- Scattered showers and isolated thunderstorms are expected later this morning into this evening, with additional showers and thunderstorms Tuesday through Wednesday.

- Low clouds and fog, locally dense, possible across parts of central and north-central WI late tonight into early Sunday.

- A few rivers will remain at or reach bankfull stage this weekend.

DISCUSSION
Issued at 409 AM CDT Sat May 4 2024

Short Term
Today
Tonight...and Sunday

Main forecast concerns will be pinning down the timing of rain today into this evening, storm chances, fog/frost potential and cloud/temp trends.

Today...a dry start to the day is expected with mid and high clouds spreading across the region. Clouds will thicken and lower from west to east, as a shortwave, low pressure and cold front approach. An area of showers associated with these features (and possible weakening MCV?) will arrive as a LLJ aids in moisture transport back into the area and we get into the RRQ of an upper jet. Still some slight timing differences, but most of central and north-central WI should see the rain by 18-19z, with the band working east and weakening across the area through the afternoon.
Additional showers and a few storms look to develop across eastern WI in the afternoon ahead of the front. Models have trended higher with rain amounts, with some CAMs showing over 0.75" in parts of central and northern WI. While the PWATs do climb to between 1.00-1.25", think the high amounts are a little ambitious as the band will be moving rather quickly. Ensembles/NBM, along with WPC, more in the 0.10-0.40" range which seems more reasonable for most spots. Instability will be tough to come by due to clouds, but a narrow ribbon of instability (SBCAPE 200-500 J/kg)is still forecast to develop/advect into eastern WI this afternoon.
This will keep the chance for a few non-severe storms going through around sunset. If storms can form during peak heating, lapse rates do steepen for a time, so a strong storm would be possible with some small hail. Not too much wind to bring down from aloft, but a weak inverted-V profile could aid in a brief gusty winds.

Highs will be coolest where the clouds/rain arrive first, with upper 50s and lower 60s expected across parts of central and north central WI. Further east, highs in the upper 60s to low 70s are expected. Cooler readings are expected near Lake MI as onshore winds are expected.

Models are again hinting at some clouds/fog across Lake Michigan as dewpoints climb ahead of the front. Little to no fog was observed yesterday (with only a little over the far southern part of the lake), and with similar moisture and water temps, would think fog chances are low. But low clouds are more likely and will add some extra clouds over eastern WI, but will hold off on any fog mention for now. Will need to monitor the area of low clouds/fog over MI and see how it behaves as it works westward.

Tonight...the rain showers and isolated storms will exit east of the area by midnight. Recent rains, decreasing winds, and at least partial clearing skies should allow for fog development, mainly across central and north-central WI. While the the HRRR is currently showing a 20-40% chance for visibilities under a mile, it is similar to what it showed yesterday when fairly widespread dense fog developed just to our west. Have added fog for much of central and north-central WI after midnight. Lows look to drop into the upper 30s and 40s for most spots. But if clouds clear a little quicker across parts of central WI, we could see temps quickly drop into the mid 30s. Frost/freeze headlines have begun from Marathon Co. southward, so a frost advisory may be needed if temps trend a little colder.

Sunday...dry conditions will prevail as high pressure builds into the western Great Lakes. Lingering low clouds and some fog is expected in the morning, especially across central and north- central WI. Some daytime cu are expected in the later morning and afternoon due to lingering low level moisture. Winds look to be just light enough for a lake breeze to develop across far eastern WI in the afternoon. 850mb temps drop back to around 3-6C, which will support highs mainly in the 60s to near 70. RHs look to drop into the 30s in the sandy soil regions, but with the recent wet weather, continued green-p and lack of gusty winds, the fire weather threat will be minimal.

Long Term...Sunday Night Through Friday

Dry start to the extended period Sunday night through most of Monday with a ridge of high pressure over the region. Deep mixing to around 4000ft Monday afternoon could lead to slightly elevated fire weather conditions with RHs falling to around 30 percent and southeast winds gusting to 20-25 mph. Fire weather concerns will be greatest across the sandy soil regions of northern and central WI where green up has not fully occurred yet.

The remainder of next week will be dominated by an initially well organized cyclone moving into the northern Plains Tuesday. Rain may begin to push into the area as early as Monday night as a warm air advection regime sets up bringing in a surge of deeper moisture with PWAT values around 1.2-1.3". Embedded thunderstorms may develop Tuesday afternoon and evening as instability increases, however, morning rain and cloud cover along with easterly winds off the lake and bay could limit the intensity of any storms that do develop. Confidence in any storms becoming severe is low at this time, however, there is still ample time for the forecast to change. In terms of rainfall amounts the long term grand ensemble (GEFS, EPS, and GEPS) shows a 30-60% for over 0.5" of QPF Monday night to Tuesday night.

Periods of showers and storms are expected Wednesday through Friday as the aforementioned cyclone slowly shifts east and weakens. The disorganized nature of this weakening system makes specific forecast details difficult to pin down. For now expect lots of clouds and periods of rain along with a few storms through the second half of next week. With the recent and forecast rainfall many area rivers and streams will likely continue near or at bank full through next week.

AVIATION
for 18Z TAF Issuance Issued at 1226 PM CDT Sat May 4 2024

A band of showers and thunderstorms was moving across central into northeast Wisconsin early this afternoon. Some of the stronger storms could produce wind gusts up to 30 knots and pea size hail.
Meanwhile, dense fog was moving northward along the Lake Michigan coastline and will impact KMTW and all the airport sites in Door County due to low visibilities or low CIGS. Another cluster of stronger storms are possible after 21z across east-central Wisconsin, mainly south of Appleton. Some of these storms could produce wind gusts to around 40 knots and hail up to one inch in diameter. MVFR CIGS are expected for a period of time behind the cold front followed by improving CIGS during the evening.
Some patchy fog is possible late tonight across central and north-central Wisconsin where skies clear the longer and winds become fairly light towards sunrise on Sunday.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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