On Saturday, temperatures on the Atlantic Ocean off of the Delmarva peninsula were above 70. By Monday, Ocean City Beach Patrol members were writing, "50 degrees, COLD!" in chalk on the back of their stands.

With a little meteorology and a lot of physics, it's easy to understand why temperatures plunged 20 or more degrees over a weekend. Strong winds blew from the south and southwest all day Sunday, forcing warm surface water further out to sea. It doesn't make much sense that the water and wind are moving at a 90 degree angle to each other, until the Coriolis effect is factored into the equation.

As the Earth spins, water in the northern hemisphere appears to be pulled to the right (west) while objects in the southern hemisphere appear to be pulled to the left (east). As the wind pushes the water out, something has to fill its place. Cold water from the deep ocean swirls up and brings phytoplankton with it. That's why the water was a murky green on Sunday.

This phenomenon is known as a coastal upwelling, and can last for weeks or just days. A few years ago, strong winds from the south persisted for the entire month of July, and water temperatures in Ocean City struggled to break 70 until mid-August. It could only last a few days, and the ocean could heat up within a week.

Check out this neat demonstration of how upwelling works. The explanation given above is the simple version, and leaves out a bunch of scientific terms like the Ekman transport and Rossby radii. To make a long story short: south and southwesterly winds make the water very cold near shore.

And recently, they have been blowing smoke from the fires in Virginia and North Carolina, which the firefighters are having a tough time putting out. On Sunday night, a slight shift in the wind brought a thick blanket of smoke down around midnight. It was awful until it rained and the winds shifted again.

With a little luck and some calmer winds, the water might be bearable by this holiday weekend.