Fog, Rain and a Warm Front at the Ferry Dock

A Foggy Thursday at Osprey Harbor

1Osprey Harbor is a fishing and ferry town on the Atlantic coast of the United States, with open ocean to its south and east. Each spring, the harbor master, Mr. Obi Mensah, lets members of the Bayside Middle School sailing club help read the weather instruments on the ferry dock. The ferry to Long Gull Island crosses only when the captain can see far enough ahead, so the dock crew watches the weather closely.

2Large bodies of air called air masses take on the temperature and moisture of the places where they form. Air that forms over cool land in spring is often cool and fairly dry. Air that forms over warm ocean water far to the south is usually warm and humid. Warm air is less dense than cool air. When air rises, it cools, and when humid air cools, some of its water vapor can condense into clouds, drizzle or rain. A front is the boundary where two air masses meet.

3On Wednesday night, a cool air mass sat over the harbor, and the forecast showed a warm, humid air mass over the ocean to the south, moving slowly north. On Thursday, club member Iris Lindqvist copied the dock readings every three hours. The morning felt chilly. By early afternoon, a gray, steady rain had been falling for hours and thick fog hid the island. In the evening the fog began to lift, and the air felt warm and sticky, even though the Sun had already set.

4Mr. Mensah also showed Iris how wind is linked to air pressure. Near the ground, air tends to flow from places with higher pressure toward places with lower pressure. When the pressure changes a lot over a short distance, the wind is usually stronger. At noon, he checked the pressure at a weather buoy out at sea and at an airport inland, both on a straight east–west line through the harbor.