The NAO

[Chris Hayes]

I posted on facebook about how it's been a record breaking April for tornadoes; beating out 2006. I then hoped we don't go into a pattern such as 2006 where everything died after April. A fellow chaser brought up computer models showing the NAO going negative pretty soon. I was wondering what affect the NAO has (and what it is exactly lol).

I was also comparing this year to spring 2008 when we had a La Nina as we do this year.

 

[Jeff House]

NAO is the North Atlantic Oscillation, and only mildly concern me about May. However we still got La Nina in our corner. The NAO is the difference in height anomalies between the central North Atlantic (35-40N) and the far North Atlantic (Greenland). Positive is the warm phase for the East; negative is cool East. The positive phase is preferred for chasing because it can promote ridging in the East if a trough is in the West, with action in between. Negative NAO can allow the reverse, and shut the Gulf, but this year I'm hoping La Nina continues to influence the West with troughs.

Those models have been trying to bring a -NAO for weeks, but having trouble carrying it forward from the 11-15 to the 6-10 day. Today they hint at bringing it forward to days 9-10, but we'll see how it goes the next few days. Even with a -NAO enough troughs in the West could still promote southern Plains action.

Just to be clear, I'm not at all concerned about the season overall. Just want to explain the NAO deal. It is just mid-April. Most years the Plains light up in May regardless. Then of course the Upper Midwest could get it next time we go back to the +NAO phase in a few weeks. Don't forget about the Panhandle and the rest of the High Plains.