What is a Beach Hazards Statement? When are they issued for Chicago beaches on Lake Michigan?

CBS News

4 days ago

A Beach Hazards Statement is issued by the National Weather Service on high swim risk days, and are largely dictated by the wind direction.
High risk days for swimming and boating are typically brought on by high winds that lead to large waves, leading to the National Weather Service's beach hazards slogan: "When the waves are high, stay dry!"
But not all windy days lead to large waves. It all depends on the wind direction.
As wind blows a greater distance, or "fetch," over open water, it piles up larger waves. Wind blowing over a short fetch has little impact on water conditions. You can see this effect by watching the upwind and downwind sides of a pond. The water will be still where the wind is coming from, and more disturbed on the downwind portion.
On days with an offshore wind – a wind blowing from land toward the water – the wind is blowing over a very short fetch of water for lakeshore swimmers, and thus has little to no impact on wave size. On the other side of Lake Michigan, however, the wind's fetch is greater, leading to larger waves.
Days with an onshore wind – a wind blowing from the water toward land – feature larger waves and more hazardous conditions as the wind blows over a larger fetch of water.
Winds in Chicago blowing from the west or south are offshore winds, leading to little impact on wave size. But winds from the east or north are onshore, leading to rougher water conditions.
Southeast winds blow onto Chicago's beaches after traveling over a 25 mile fetch of water from Indiana. East winds create larger waves, blowing over a 50-mile fetch from Michigan. Chicago's largest waves and most dangerous beach conditions come from north-northeasterly winds that blow over 275 miles of open water – the entire length of Lake Michigan.