The backdoor cold front has passed and now strong, post-frontal full fetch north/northeast winds have taken hold and are sweeping off Lake Michigan over Chicago’s shoreline.

Little wonder the winds are strong–with gusts from 30 to 40 mph being reported up and down the western Lake Michigan shoreline. Gusts have reached 32 mph at the Harrison-Dever Crib 3 miles off the north Chicago lakeshore, but have reached 41 mph up the lake in Sheboygan. These winds are sweeping into the area beneath the southern flank of, by late-spring standards, an impressive 1037 mb (30.62″) Canadian high pressure centered over Canada’s Ontario province. That a very respectable high pressure for this time of year.

Here’s a windy.com depiction of the “full fetch” NNE winds blowing down the length of Lake Michigan. The reference to “full fetch” winds means winds are blowing southward the length of Lake Michigan. That’s important because this offers the wind time to transfer its kinetic energy to the lake surface building waves. It’s no accident the highest waves to sweep onto Chicago beaches occur in “full fetch” wind set ups like Wednesday’s.

Here’s a model forecast off the Weather Service’s 3km HRRR showing the the full fetch winds blowing the length of Lake Michigan. Colors on this depiction indicate wind velocities. The GREEN AND YELLOW shaded areas are the regions with the strongest winds.
Wednesday morning surface weather map showing a well developed 1037 mb (30.62″) high pressure centered over Ontario province in southern Canada. The winds beneath its southern flank are strong.

Lake Michigan’s surface has been churned by the strong post cold frontal winds

It’s been interesting watch the impact on Lake Michigan Wednesday morning–the change in the lake state has been quite dramatic in the opening hours of the day.

The initially quiet lake surface at an just past daybreak Wednesday has been replaced by well developed southbound waves sweeping onto Chicago beaches with whitecaps. Video from the Edgewater shoreline.

A broken deck of low, post frontal stratus clouds with evidence of Canadian smoke is now sweeping southward along and over the Chicago shoreline hiding the sun on occasion.

What’s ahead Wednesday

The stage is set for a cool, windy day with temps far lower than Tuesday’s July level 80s–in fact anywhere from 20 to 30-deg cooler–the equivalent of moving from a July-level temp regime back to late April temp levels. Daytime temps Wednesday will retreat to the 60s inland and fall back to the 50s along the Lake Michigan shoreline.

Were this swimming season or a weekend with southern Lake Michigan populated by mariners, concerns over the rip-currents and growing wave heights would be front and center in the wind whipped Lake Michigan waters.

I’m posting a series of wave height forecast panels which you can cycle through and watch what amounts to a model forecast of how wave heights will continue building as the full fetch “NNE” winds run the 280 mile length of Lake Michigan–allowing plenty of time for energy transfer from the wind to the lake surface building waves into a 6 to 9 ft. range along the Chicago shoreline and offshore waters. A SMALL CRAFT ADVISORY IS IN EFFECT through 7am CDT Thursday.