The radar loop above starts on Thursday evening, October 1 and runs through Sunday evening (thanks to Matt Daniel at WMAZ in Macon, Georgia).
A similar video — showing a narrow band of intense moisture — could be shown for the 2010 mid-Atlantic “Snowmageddon”.
Some have suggested that Japan’s extraordinary flooding in early September reflected meteorological conditions similar to what we saw last week over the Carolinas.
Detailed data does not exist to show the unfolding of the 1861 California megaflood. According to Scientific American, this 43-day storm, “turned enormous regions of the state into inland seas for months, and took thousands of human lives. The costs were devastating: one quarter of California’s economy was destroyed, forcing the state into bankruptcy.”
“Geologic evidence shows that truly massive floods, caused by rainfall alone, have occurred in California every 100 to 200 years. Such floods are likely caused by atmospheric rivers: narrow bands of water vapor about a mile above the ocean that extend for thousands of kilometers.”
The emergence of so-called atmospheric rivers is well-established, but not widely understood. NOAA explains, “Atmospheric Rivers (AR) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. While ARs come in many shapes and sizes, those that contain the largest amounts of water vapor, the strongest winds, and stall over watersheds vulnerable to flooding, can create extreme rainfall and floods.”
In 2011 USGS, FEMA, CalEMA, and others collaborated in the ARkStorm exercise focusing on a recurrence of the historic pattern in California. Scenario elements include, “The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricane-force winds. Across wider areas of the state, winds reach 60 miles per hour.”
What is important to recognize is that this is not worst-case thinking, but historically demonstrated risk. It is not so much a matter of if, but where and when.
And by the way, this winter’s El Nino is predicted to be strong, especially in Southern California.