Thoughts about the upcoming 2015 chase season

[Jason Harris]

Down in Bryan/College Station TX it's looking like Spring is on the move. Birds chirping, crane flies coming out, folks searching for snakes that are coming out of hibernation, and dewpoints in low 60s with temp expected near 80 today. Storm system tonight and tomorrow and supposedly stronger one Fri/Sat. Even a hazardous outlook posted for SE TX with chance of spotter activation. SPC has a 5% for Eastern TX. No word about tornadoes as of yet, but note the 150-200 1 km helicity forecast on the NAM about 24 hours from now in S. Central TX and then creeping up to 250 in N. Central for Fri . Not seeing CAPE beyond 500, but just for the sake of speculation--and remembering the odds are against a truly tornado-less March, maybe a brief and nearly invisible spin-up amid some heavy showers Wed. or Sat.?

 

[Jeff Duda]

Don't look now but...

MJO!

I've been watching this for several days now. A similar intense pulse was seen in the past 90 days in phases 5 and 6 but it quickly died down. This one is strengthening. It is my understanding that U.S. tornado activity is linked in some way to the strength and phase of MJO activity. IIRC, tornado activity may be increased when the MJO is in phase 2 during the spring. Not exactly where the MJO is right now, but I think having an active pulse is better than not having one. Also, when there are competing factors like a strong positive PDO with a CPW ENSO event and an MJO event, I'm not sure the MJO can overwhelm the PDO. Also, saying "increased tornado activity" as we pass through March is like saying it's gradually getting warmer in the Northern Hemisphere as we transition into spring. So take it for what it's worth.

 

[chrisbray]

Don't look now but...

MJO!

I've been watching this for several days now. A similar intense pulse was seen in the past 90 days in phases 5 and 6 but it quickly died down. This one is strengthening. It is my understanding that U.S. tornado activity is linked in some way to the strength and phase of MJO activity. IIRC, tornado activity may be increased when the MJO is in phase 2 during the spring. Not exactly where the MJO is right now, but I think having an active pulse is better than not having one. Also, when there are competing factors like a strong positive PDO with a CPW ENSO event and an MJO event, I'm not sure the MJO can overwhelm the PDO. Also, saying "increased tornado activity" as we pass through March is like saying it's gradually getting warmer in the Northern Hemisphere as we transition into spring. So take it for what it's worth.

Hate to be a noob, but, how do I read or interpret this? lol

 

[chrisbray]

I Wiki'd it and apparently when it is outside of that circle in the middle, it is a strong pulse and that leads to increased tropical moisture coming from the western pacific all the way across to the US West Coast

 

[calvinkaskey]

http://www.weather.com/news/weather/video/el-nino-la-nina-and-tornadoes

 

[Andy Wehrle]

That's one way to look at it. I've also read a lot of studies claiming that El Nino increases tornado probabilities across the southern states due to the jet stream being further south. The frustrating thing is that most such analysis seem to focus on the ENSO phase during the winter months, not the phase during the spring (i.e. the Plains chase season).

There's so much conflicting information out there, it's certainly a gross oversimplification to just say "La Nina (El Nino) increases (decreases) the risk of tornadoes and thus makes for a better (worse) chase season." The one conclusion I've heard that seems to have some teeth is that the extremely violent outbreaks tend to occur when the phase is transitioning out of a strong La Nina. This was the case in both 2011 and 1974.

Anyone know what the ENSO situation was for Palm Sunday 1965?

 

[Adam Adkins]

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

 

[Andy Berrington]

Anyone know what the ENSO situation was for Palm Sunday 1965?

Weak Nina transitioning to a strong Nino.

 

[Andy Wehrle]

So maybe, in broad terms, transition > phase?

 

[Donnie Beasley]

That's one way to look at it. I've also read a lot of studies claiming that El Nino increases tornado probabilities across the southern states due to the jet stream being further south. The frustrating thing is that most such analysis seem to focus on the ENSO phase during the winter months, not the phase during the spring (i.e. the Plains chase season).

There's so much conflicting information out there, it's certainly a gross oversimplification to just say "La Nina (El Nino) increases (decreases) the risk of tornadoes and thus makes for a better (worse) chase season." The one conclusion I've heard that seems to have some teeth is that the extremely violent outbreaks tend to occur when the phase is transitioning out of a strong La Nina. This was the case in both 2011 and 1974.

Anyone know what the ENSO situation was for Palm Sunday 1965?

Hi Andy, you have the right idea, just a bit backwards. It would be coming out of a strong El Nino and transitioning straight into a La Nina that has shown to produce years with extreme outbreaks. 1999 was also one of these years and featured the May 3rd tornado with the highest winds ever recorded as well as the largest single day outbreak in Arkansas history.

 

[Donnie Beasley]

So maybe, in broad terms, transition > phase?

This does seem to be the case, specifically with El Nino's transitioning straight into La Nina's.

 

[Donnie Beasley]

http://www.weather.com/news/weather/video/el-nino-la-nina-and-tornadoes

And your point? That video shows absolutely no facts. Just makes a very broad generalized statement. Unfortunately I can't read the article they reference due to not being a paying member of the website it is located on. Here are a few quotes I took from the little bit I was able to read.

"However, limitations12 of the severe thunderstorm observational record, combined with large year-to-year variability12, 13, have made it difficult to demonstrate an ENSO influence during the peak spring season."

This should tell you all you need to know.

We show that fewer tornadoes and hail events occur over the central US during El Niño and conversely more occur during La Niña conditions.

Okay, we already know that. No one is saying that El Nino years are going to produce more tornadoes than La Nina years. We are saying that El Nino years can still produce above average numbers of tornadoes with large outbreaks. The little bit of this article I was able to read doesn't have any facts to prove otherwise. Keep trying Calvin.

 

[Dan Robinson]

Scratch my last post, the models always ding me as soon as I try to say something about the pattern +7 days out. Back into hibernation mode.

 

[Verne Carlson]

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

 

[Donnie Beasley]

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

That is the article that was referenced in my previous post. That's not really what it is stating at all. It's simply stating that more tornadoes typically occur during La Nina years than El Nino, which we already know. It doesn't say anywhere in the article that El Nino years typically produce below average numbers of tornadoes or outbreaks. In fact, it doesn't mention tornado numbers at all, that I can see. If a La Nina year produces 1700 tornadoes and an El Nino year produces 1300, does that mean the El Nino year was a bad year for tornadoes? I will take 1300 hundred tornadoes any year. That's a good year to me.