Weather Sensors

Weather Terms:

What's measured by the weather station on the roof above you?

The meters on the left report the current weather from instruments on Pacific Science Center's roof.

This information is stored on the computer to the right which sends it to computers at KING 5 and the National Weather Service.

Wind speed and direction
Winds are referred to by the direction from which they blow. A north wind is one which blows from the north.
In Seattle, a north wind usually means a high pressure system and dry weather are approaching. A wind shift to the south usually means the approach of a low pressure system and wetter weather.

Relative humidity
Relative humidity is a percentage of moisture in the air as compared to the maximum amount of moisture the air can hold. This maximum varies with temperature-warm air can hold more moisture than cool air.

Temperatures in Western Washington tend not to be as hot or as cold as temperatures in Eastern Washington. This is because water heats and cools more slowly than land. Because Western Washington is surrounded by the Pacific Ocean and Puget Sound, air temperature changes more slowly than in Eastern Washington, where water is scarce.

Wind chill/heat index
The combination of temperature, humidity and wind speed can make the air feel hotter or cooler than the actual temperature. Wind makes us feel cooler. High humidity makes a hot day feel hotter.

Dew point
Dew point is the temperature at which air becomes saturated, or unable to hold additional moisture. Warm air can hold more water vapor than cool air. When the temperature drops during the night, the air can't hold as much moisture, and dew forms.

Barometric pressure is a measure of the weight of the air pressing down on us. Cold, dry air weighs more than warm, moist air. Watching how the pressure changes over time tells more than the pressure alone. Rising pressure usually indicates that a high pressure system is approaching, typically bringing clearing skies. Falling pressure usually means a low pressure system is approaching, often bringing clouds and precipitation. Rapid changes in pressure warn of strong winds.

The sun's rays provide the energy that drives the weather. This meter shows the current percentage of sunlight relative to the amount of sun at noon on a clear summer day.

The average rainfall in Seattle is about 38 inches per year.

Average rainfall in inches

January 6.0"
February 4.2"
March 3.6"
April 2.4"
May 1.6"
June 1.4"
July 0.7"
August 1.3"
September 2.0"
October 3.4"
November 5.6"
December 6.3"