Thoughts about the upcoming 2015 chase season

[Brett Roberts]

FWIW, I've calculated correlation coefficients between ENSO and my objective chase season scores. I've found essentially no correlation for the southern Plains, and a weak negative correlation for the northern Plains (using ONI, where El Nino is positive and La Nina is negative).

A few plots:
Plains as a whole
Northern Plains
Southern Plains

Based on these data and composite SSTA plots I produced using the "top 20" and "bottom 20" chase years, I believe there is some truth to the idea that La Nina is more favorable for active northern Plains years. For areas from I-80 southward in chase country, though, it looks like a wash (no signal).

Subjectively, my impression is that La Nina could be more favorable for large/intense outbreaks east of the Plains, such as the Midwest and Mid South. However, in my opinion, this is largely irrelevant to storm chasing. If you're looking for deadly megaoutbreaks ravaging Illinois or Tennessee, El Nino might be bad news -- if you're looking for quality dryline setups in Kansas, it doesn't really matter. I would hope most of us on this board are more interested in the latter. The two most recent "true" El Nino events, 2006-07 and 2009-10, happen to have preceded arguably the best chase seasons of the last decade (both of which had numerous good northern Plains events, illustrating how even that signal is weak).

 

[Clarence Bennett]

To add a little more to the El Nino vs. La Nina discussion, one of the more prominent features of an El Nino season (most notably March/April) is a more active southern stream jet at 250mb. This tends to limit more northward transport of deeper moisture. It doesn't mean you can't/don't get it, but it does hinder it. During a La Nina episode of ENSO, this strong southern stream jet is pretty much absent. History says if you want big outbreaks and lots of tornadoes, La Nina will get it done for ya.

 

[jaredleighton]

Ran across this article.. basically stating La Nina good/El Nino bad for tornado season: <<LINK>>

To go along with that article...here is the article/paper that your linked article apparently is referencing. John Allen at least used to post on here, but I haven't seen him pop up recently. Anyway, he just published the article in which he shows how the ENSO cycle affects the tornado season.

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2385.html

In a nutshell moderate to strong El Nino in Dec/Jan/Feb means a below normal tornado season for the plains, while a moderate to strong La Nina means the converse. I asked him what a weak El Nino means, and he told me that the signal was muted. So I'm not sure that our current ENSO status means much for the plains.

 

[Jeff Duda]

So I'm not sure that our current ENSO status means much for the plains.

Basically it doesn't mean anything. The full impacts from an ENSO event occur in the northern hemisphere winter, with impacts trailing off into the spring.

 

[Paul Knightley]

The link shown above (another story based around it here also http://www.earth.columbia.edu/articles/view/3239) is to a comprehensive study which, rather than linking tornado number per se to ENSO, links the overall synoptics with ENSO. When Harold Brookes pops up and states that this is the first study to link ENSO to large scale patterns which favour (or not), rather than just focussing on reports, it's worth a serious look. There have been tentative statements over the last several years about La Nina favouring violent outbreaks over El Nino, but this appears to be something more concrete. As mentioned above, though, studies such as this tend to focus on the more robust episodes, and rightly so. All in all it suggests that the large-scale pattern this season will not favour multiple severe outbreaks, but as El Nino is weak, it would lean towards not a major suppression either. However, as I mentioned above, the PDO appears to be the main driver (and has been for about the last year at least) - it is very strong at the moment and favours western ridge-eastern trough...so it maybe that this dominates and the ENSO signals is much less relevant.

 

[Andy Wehrle]

So the million-dollar question is...when does that PDO weaken?

 

[Brett Roberts]

So the million-dollar question is...when does that PDO weaken?

Absolutely no sign of cooling SSTs across the northeastern Pacific as of this week. If those warm SSTs are in fact a dominant driver of the nauseating hemispheric pattern we're stuck in (not claiming that's definitely the case), this spring is going to be as bad or worse than the last few.

Of course, we were stuck in this same type of pattern (at least over the CONUS) through much of March-April 2013 and 2014. In 2013, the PDO was negative; last year, it was just starting to go positive. Wouldn't it just figure that, perhaps, we found other ways to squander a three-year stretch of favorable -PDO conditions during 2011-2013.

 

[chrisbray]

If we get nothing on Tuesday you can almost bank on a tornado-less March!

 

[Michael Gavan]

Tuesday and Wednesday don't look like tornado days to me, but severe weather nonetheless....and that's step in the right direction. Maybe once the NAM gets a hold of it there will be something to look at. Either way the GFS brings one of those strong deep south cold fronts into the Caribbean after this. GFS really wants to bring a few boomers into west Michigan on Wednesday. I'm good with that.

 

[James Gustina]

The shear values definitely don't blow me away for Wednesday at the moment. Everything else is relatively there, that turning just doesn't materialize in the lowest 3 km. Its also likely going to be eastern Oklahoma which adds a whole different element of nope.

 

[Adam Lucio]

Tuesday looks like a cap bust. Wednesday I can see a nice squall line type event. Those who are desperate better get out and get a small fix, what comes after that is not pretty!

(image may be time sensitive)

 

[Stephen Szulborski]

Tuesday looks like a cap bust. Wednesday I can see a nice squall line type event. Those who are desperate better get out and get a small fix, what comes after that is not pretty!

(image may be time sensitive)

At least with the Euro, the Gulf quickly recovers after being blasted around day 7.

 

[Jared Orr]

Tuesday looks like a cap bust.

I think it's faarrrrr too early to be making that call. With a little sounding modification and as much forcing we're going to be seeing, we could very easily have some broken line segments.

 

[Michael Snyder]

If anyone has a site or the raw data that breaks down Tornadoes by month back to JAN 1950, I have a nice Excel spreadsheet that I can break down the Tornado data month by month based on ENSO temps.

Something everyone seems to do is break it down by El Nino/La Nina years. El Nino and La Nina being based on a 5 month running average of course.

I have started just breaking it down by actual monthly ENSO water temps, regardless of whether an El Nino or La Nina officially occurred or not. This method allows for ALL months to be included and shows some interesting patterns.

So far all of my work has been with Pacific Northwest snowfall, rainfall, temps vs ENSO temps. I havent even started plugging tornado data into this spreadsheet yet. Im kind of interested in what it might have to say...

Anyone have any good links?

Thx
Snyder

 

[chrisbray]

Calling this one a month in advance, book it!