What Are Shelf Clouds?

Thursday, August 11, 2016 several strong thunderstorms passed over the Cleveland suburbs. Many viewers submitted photos of stranger cloud formations with some speculating that there tornadoes. What are these clouds?  Are they a rare phenomena?  Not really. These are called shelf clouds or Arcus Clouds. They are fairly common around thunderstorms even in northern Ohio. I blogged about shelf clouds over 10 years ago!

What are shelf clouds? The National Weather Service has a great description.

Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. Remember, shelf clouds are not tornadoes or wall clouds. These are formed when rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. When this warm, moist air condenses, you see the shelf cloud. 

Normally, you will feel a burst of cooler wind followed by rain and maybe hail. The higher gusts occur on the back edge which can cause downed trees and power outages. So when the next storm develops, look for the Arcus Cloud. Remember that tornadoes normally don't accompany these cloud formations just gusty winds, rain/hail then the highest winds toward the back end.

June 15th to July 17th Temperatures Since 1991

We are in the midst of our first heat wave across northern Ohio.  Temperatures will stay above 90 for several days until the heat pushes back to the west late this weekend.  Is this type of heat across the country common or a rarity?  Below is a plot of temperatures compared to normal for JUNE 15th through JULY 17th for each of the last 20 years starting with this year.  Warmer colors indicate temperatures above normal.

Check out 1998 and 1994.  The heat looks very similar to what has been going on most of this summer.

Notice the core of the heat in Oklahoma and Texas

Heat last year was along the East Coast, Washington, D.C.

Two year ago, the heat was once again over Texas

Heat in 2008 was along the West Coast. Cooler in the Great Lakes

Heat in 2007 in the Pacific Northwest

2006 featured heat in the norther tier and out West

2005 heat:  Central Plains

Very little heat here

Cooler temps from Texas to New York

Heat across the northern 1/2 of the US

Heat out west in 2001

Heat in the deep south/cooler north

Heat in New england, cooler in the deep south

Look familiar? Heat across Texas and Oklahoma

Temps stayed near normal

Heat over Texas; cooler in the Great Lakes

Well below normal out west; heat in Canada

Look familar? Heat in Texas, New Mexico and in New England

In 1993, heat was located East

Temps well below normal across most of the US

Heat across the Great Lakes; cooler than normal out west

UNBELIEVABLE Storm Clouds

Something you don't normally see in Ohio is a "Shelf Cloud" or an Arcus Cloud. Last night, a squall line developed around 8PM and produced a fast-moving Arcus Cloud. They rarely produce any rain themselves. Its the massive Cumulonimbus Clouds behind the Arcus Cloud that contain the rain/hail/severe weather.

Arcus Cloud - Northwest View

Arcus Cloud #2

Arcus Cloud - West View

Mammatus Cloud - After Arcus Cloud Passage