Video of mammatus clouds by Jason Asselin
Though they may be associated with severe thunderstorms, mammatus clouds, like the ones in this popular Youtube video, are not necessarily an indication of severe weather.
Mammatus clouds form when air sinks, unlike most clouds which form due to rising air. This results in the pouches of condensation that give these clouds their bumpy appearance.
The turbulent atmosphere that creates these "upside down" clouds can be conducive to thunderstorms. Generally, a severe thunderstorm is eminent if mammatus clouds form on the underside of a cumulonimbus cloud. If they form beneath an anvil cloud, however, they are typically not threatening.
Asselin said that the video was taken around 8 p.m. CDT on July 22, and AccuWeather.com Expert Senior Meterologist Paul Walker said that coincides with a cold front that moved through the area. The high for that day around Iron Mountain, Mich., was 85. The day was also marked with high humidity. When the cold front moved through, it pushed down from atop the warm air and created the pockets in the clouds.
There were some thunderstorms in the area, but the temperatures evaporated much of the precipitation, leaving no measurable rainfall.
Thumbnail image by Phyllis Carlson, courtesy of AccuWeather.com Astronomy on Facebook.
The risk of drenching and locally gusty thunderstorms will expand northwestward over the balance of the week, reaching parts of Southern California, Arizona and Nevada.
While the heat wave and high humidity will recede in the Northeast to finish out the week, 90-degree F air may linger in many areas into August.
The Stockholm Arlanda Airport in Sweden is giving travlers a chance to sample weather at various destinations around the world through the use of the Climate Portal.
The Dead Sea is disappearing at an alarming rate, leaving behind thousands of sinkholes that are chipping away at the coastline's vibrant and touristy atmosphere.
Gulf Coast (1995)
Tropical storm Dean entered the Texas coast near Galveston, TX. Galveston reported a wind gust of 51 mph, but just 0.54" of rain. Coastal roads were flooded across Louisiana.
Las Vegas, NV (1998)
2.50 inches of rain in 1 hour.
Greenville, SC (2004)
Heavy rain causes nearby river to crest at 19.2 feet, the second highest crest ever.