New Method May Accurately Forecast Hazardous Weather

Washington: NASA scientists have developed an improved forecasting method to identify where severe winds, hail or tornadoes are more likely to occur within storm clouds, by combining satellite images with novel algorithms.

"We are able to analyse the locations where severe storms most frequently occur and when they occur with unprecedented detail using commonly available satellite imagery," said Kristopher Bedka, a physical scientist at NASA's Langley Research Centre.

Researchers studied hazardous thunderstorms with satellites across the globe from the National Oceanic and Atmospheric Administration, NASA and other international agencies.

Thunderstorms form when warm, moist air rises rapidly into the atmosphere. These air currents produce cloud formations known as cumulonimbus incus, or anvil clouds, which look similar to an atomic bomb explosion with a flat and wide top, researchers said.

The flat anvil tops form because when updrafts rise through the lowest layer of the atmosphere, they hit the layer above, known as the stratosphere, without penetrating it, they said.

These updrafts usually flatten wide and spread under the stratosphere, but some of them are intense enough to punch through the stratosphere, researchers said.

These extreme updrafts are the ones forecasters should be most concerned about, they said.

Forecasters have known for years that anvil clouds indicate thunderstorms. But anvil tops can be miles wide, and it is sometimes difficult to distinguish where within those clouds hazardous weather may be occurring, researchers said.

Bedka said it is crucial to figure out what is a hazardous storm and what is not within anvil clouds, especially because strong updrafts pose serious risks for things like flying aircraft.

"You never really want to fly through turbulence, but you cannot tell a forecaster or a pilot: 'do not fly anywhere here,'" he said.

Researchers focused on updrafts that are strong enough to punch into the stratosphere. That penetration creates lumpy clouds, which look almost like the top of a cauliflower sticking out from an anvil top.

Known as overshooting tops, these lumps indicate areas where strong thunderstorms - sometimes hail and tornadoes - usually occur, researchers said.

Analysing sunlight reflected from clouds allowed them to see the signature cauliflower shapes of overshooting tops.

They also used infrared imagers that function like night-vision goggles to detect heat. These imagers can spot overshooting tops, which emit less heat than other clouds in lower regions of the atmosphere.

To deliver almost instant forecasts, researchers combined their satellite observations with powerful software engineering.

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