Feb 06, 2008
Tornadoes Rip Through South in Typical La Nina Fashion
By Joseph D’Aleo, CCM
...Tornado outbreaks are more likely in La Nina years. A few years ago, I did a study of the years with the maximum number of tornadoes for every month and found that from the fall to the spring they were all La Nina years. The Superoutbreak of April 1974 came after one of the strongest La Ninas on record. And Eugenio Hackbart at the METSUL reminded me also in a similar La Nina in a cold Pacific era, in February 1971, more than 100 people died during an outbreak in the Mississippi Delta.... An unpublished manuscript by Knowles and Pielke (1993) observed that tornadoes during ENSO cold phase (La Nina) are stronger and remain on the ground longer than their warm phase (El Nino) counterparts. They further showed that there is an increased chance of large tornado outbreaks (40 or more tornadoes associated with a single synoptic system) during ENSO cold phase (La Ninas). Given the strength of this La Nina, what it has been able to do in January and February and that history, we might expect a very stormy spring from the south to the Ohio Valley.
In La Ninas, the cold tends to want to stay across the north and strong warmth builds at times across the south. Storms along the boundary feed on the contrast and severe weather often results. To the north of the storm track, it is ice or heavy snow that is the problem and that will be the story over the next few days.... Thunderstorms will likely be in the cards further south until the cold air begins to filter back in and be reinforced this weekend with an arctic blast. Wild swings as we said a few months back are also typical of La Nina.
Interesting. Thanks for the info.
SALEM, Ore. (AP) — Heavy winter snow and rain are setting up conditions similar to the 1996 flooding that caused hundreds of millions of dollars in damage across much of the state.
The heavy snows 12 years ago were followed by warm storms with heavy rains that combined to flood most of the Willamette Valley and the major cities of Oregon.
On Tuesday, the 12th anniversary of the first day of heavy rains that triggered the flooding, even more snow had fallen than in 1996, officials said.
"It's entirely possible we will get one of the dreaded rain-on-snow events," said George Taylor, an Oregon State University climatologist.