User blog:SilentShadow87/La Niña dissipates - but don't write this tornado season off just yet

The latest models have shown La Niña is dissipating, with the IRI forecast suggesting that ENSO-neutral conditions are most likely throughout this year's tornado season (with a 70% chance of ENSO-neutral conditions for the FMA period, roughly 60% for the MAM to AMJ period, and 50% for the MJJ period. By the time we get into summer, models begin to favour El Niño, with a 45% chance of El Niño in the SON period). A graph from IRI showing the ENSO probabilities is shown below for convenience. As I'm sure everyone knows, La Niña is considered to create a favourable environment for tornadoes to develop, while El Niño has the opposite effect. So, does this mean the 2017 tornado season will be a total bust?



Not necessarily. To begin with, the effects of El Niño and La Niña don't end immediately after the Niño or Niña dissipates - it usually takes several weeks at least to transition. Second, and more importantly, I recently came across this very informative post on the Stormtrack forum discussing the little-known connection between the MJO and high numbers of tornadoes, as well as strong/violent tornadoes. "Forecasting" the MJO really is wild guessing based on a few clues, but the gist is that Phase 2 of the MJO cycle appears to be favourable for tornadoes and tornado outbreaks. The MJO doesn't always stick to its own cycle - sometimes the oscillation is erratic - but at this point it looks like Phase 2 might be in effect by early March, which means that if verified, March could be an active month, possibly extending into April.

El Niño is also generally considered to be favourable for fall and winter tornado outbreaks. Notable examples are the Widespread Outbreak of 1992, the Benton, Arkansas outbreak of 1997, the 2002 Veteran's Day outbreak, and the December 23-25 and 26-28, 2015 outbreaks.

The full Stormtrack post:

The full post: https://stormtrack.org/community/threads/upcoming-chase-season-2017-edition.29511/#post-347432