How Water Vapor Satellite Images Work:
Most of the satellite weather images that we see are created by satellites that sit about 22,500 miles above the earth. These satellites are stationary above a particular point on earth, so they always show the same view of the earth, 24 hours a day, 365 days a year.
Each satellite has numerous sensors that view the earth in slightly different ways. The water vapor sensor detects water vapor in the middle and upper parts of the atmosphere. This is one of the most powerful tools for detecting storms.
Water vapor is always present in the atmosphere, even when it feels very dry and there are no clouds. Water vapor satellite images allow you to see the movement of the air even though the water vapor in the air is invisible to the naked eye. The visible clouds that we see with our eyes are made of tiny liquid water drops or of tiny ice crystals, which are detected with a different satellite sensor.
The purple in the satellite image above shows areas where there is more water vapor in the middle and upper part of the atmosphere, while red areas show areas with less water vapor. There is an area of spin indicated over Seattle and “ripples” over northern California and Oregon. Identifying these air motions is only possible with a water vapor image because these locations have no clouds for satellites to detect.
How does a water vapor satellite image help you find snow?
Storms in the atmosphere spin counter-clockwise in the northern hemisphere, and areas of spin in the atmosphere act to lift the air. When air is lifted, the air expands due to lower pressure, cools, and the moisture in the air condenses into snowflakes or raindrops. Finding areas of spinning air is very helpful for forecasters. Many times, finding areas of spin is easiest with water vapor images because it allows you to see the air spinning even if there are few or no clouds.
Limitations of Water Vapor Satellite Images:
The satellite images show water vapor in the atmosphere and not the precipitation that is falling on the ground, so the presence of water vapor doesn’t necessarily mean that it is snowing. A water vapor satellite image is just one tool in the weather forecasting & powder chasing tool belt.
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