La Nina & Tornadoes

It looks like the current La Nina is expected to continue through the spring of '08. Well, first let's start with what La Nina is. It is when the sea-surface temperature of the tropical Pacific Ocean is cooler than normal.

When was the last La Nina? A mild La Nina last occurred in 2001.

So what does that mean to us and how does it relate to tornadoes? Well, the year that Minnesota saw the most tornadoes was in 2001 (Remember Northfield and Siren, WI-just to name a couple). Since the jet stream plays an important role in severe weather, the position of the jet stream can determine what parts of the country are more likely to get tornadoes. During La Nina, the position of the jet stream often extends from the Rocky Mountains in an east/northeast direction to the Great Lakes. That means that severe weather is likely to occur farther north than normal.

Here is a list of the # of tornadoes in MN by year:
1999 = 36
2000 = 33
2001 = 74 (one-year record for MN)
2002 = 34
2003 = 47
2004 = 58
2005 = 68
2006 = 25
2007 = 18 (the fewest in one year since 1990)

So, it could be an active year. And a footnote to the Siren, WI tornado of 2001--that same storm system produced a tornado earlier it it's lifecycle, and it touched down near Braham.