Chaser traffic in 2012 and the "CTI" (Chaser Traffic Index)

[Jake Orosi]

If those dots are representative of all chasers then I’d say there wasn’t much of a problem. Have you ever chased on the plains? I’m guessing that you have not. I never show up as a dot and I know there are others that aren’t on SN either. Without a question there were many more cars on the road because of the storm than shown by those dots, and from what I saw elsewhere many were local lookers. I don’t have a bit of a problem with that by the way, cause if I lived there I’d be out looking also. Both contribute to the numbers. It’s hard to come on a forum for chasers and be critical of chasers without many of them just tuning it out. This is coming from a guy that is rather critical himself of some stuff that goes on.
I've only been making trips 5 years or so, but I think you would say things differently if chasing was a part of your life and you had experience on the plains.

I don't doubt it; but the value is in having a different and unattached perspective. A highly invested chaser isn't going to be objective, they're going to be defensive and dismissive.

 

[Dan Robinson]

I found this interesting quote from a 1996 article describing an event in Oklahoma in 1991:

http://www.cimms.ou.edu/~stumpf/twistint.html

Already these days, real chasers have to contend with news crews and thrill-seekers clogging roads on their way to capture footage of tornadoes. With this movie, they can envision a bad situation getting worse. Richard Thompson recalls a set of 1991 storms in Oklahoma that drew a caravan 100 cars long. "It was that bad," he said.

 

[Jason McKittrick]

The Oregon, MO day in 2009


I was there and it was at least a CTI-5. I am not sure how many others witnessed this, I think it was in Maysville, where the sheriff closed the main intersection in town to allow the carivan to go through town without having to stop at the signal.

 

[Robert S. Thompson]

I would rate the Oregon MO day at 6 or 7. Ideal situation for massive convergence - a weekend, a down year with few other opportunities, a few slow moving supercells (and not much else to spread people apart). Also, most chasers had arrived the day before the Oregon storms because storms had been predicted for that day in the same general area (ended up being a cap bust).

RST

 

[Dan Robinson]

I've been thinking about the possibility of forecasting chaser numbers.

Based on observation, the theory is that storm chaser numbers increase when the following conditions are in place:

- Weekend or Holiday
- Proximity to a city
- Southern Plains region
- Fewer target storms
- High-end SPC categorical risk

Formula for calculating expected CTI:

(M+C+R+S+D)-(T-1) = CTI

- Where (M) is Month value:

July-February = -1
March = 0
April = 1
May = 2
June = 1

- Where (C) is proximity to a city:

Within 100 miles of major city = 2
Within 200 miles of a major city = 1
More than 200 miles from a major city = 0

- Where (R) is the geographic region:

Southern Plains (northern Texas, Oklahoma, southern Kansas) = 2
Central Plains (northern Kansas, Nebraska) = 1
Northern Plains (Dakotas) = 0
Midwest, South, Atlantic Coast = -1

- Where (S) is the SPC categorical risk:

General, 2% tornado = -1
Slight, <=5% tornado = 0
Slight, 10% tornado = 1
Moderate, 15% tornado = 2
Moderate, <=10% tornado = 2
High, <=15% tornado = 2 (wind event)
High, >=30% tornado = 3

- Where (D) is the day of the week:

Weekday = 0
Weekend or Holiday = 1

- Where (T) is the number of dominant, mature tornadic supercells within the risk area.

The maximum theoretical CTI would then be 10, which would occur:

- on a weekend or holiday
- in May
- inside of a SPC high risk
- close to a major city
- in the southern Plains
- one dominant supercell

The minimum would be zero (even if the calculated CTI was below zero).

I know this isn't perfect, but would be interesting to refine and see how it validates.

Any comments or observations?

 

[Skip Talbot]

Maybe a 3 tomorrow in SD? 2+0+0+1+1-1? Not too shabby.

 

[Jacob Ferden]

My God, how long did it take you to come up with all that? That's brilliant.

 

[Dan Robinson]

Thanks - slow day at work today

I've also wondered about dynamically generating a CTI forecast based on realtime data.

It might go something like this:

(STP/2)+(SC/5)+M+C+R+D = CTI

Where STP is the significant tornado parameter, SC is the supercell composite parameter, and all of the other variables are the same as before. You could integrate R and C values into a map grid (with M and D being pretty straightforward) and then overlay the STP/2+SC/5 for any point on the map. Those are just rough-guess divisors for the STP and SC.

Spotter Network data may or may not be another way to generate an expected CTI. We'd first have to figure out what percentage of chasers use SN, then we could estimate the actual number of chasers on the road. Many chasers don't turn on their beacons until the chase is under way (and in some cases, not until they're on a storm). This issue might be solveable by finding a reliable ratio of chasers beaconing at 6PM to the number beaconing at 10AM (IE, something like 10 to 1). I'd assume this ratio is never consistent enough day to day to be of any use, though. If it was consistent, you could reliably forecast the maximum theoretical number of chasers to end up on a single storm (or multiple storms). Either way, SN would be a great validation tool to refine the formula after each event.

 

[Dan Robinson]

Using the theoretical formula, today is going to probably be a high end "6" chaser traffic day, but if we end up with one storm, it could be higher given it's Memorial Day weekend (the season maximum in vacationing chaser numbers). The only thing tempering this event is the fact that today was originally expected to cap bust, and most everyone who chased in WI yesterday is not going to be able to travel the required distance in time (at least safely) to make the Kansas target.

I think the original formula might need a tweak to add a point or two for Memorial Day weekend events. If it weren't for WI yesterday, today could have been the worst chaser traffic day in history. I'd expect the problem to be significant today, maybe critical, if that triple point goes.

 

[Brian Hurst]

It was maybe a 2 yesterday (5-25-12) most congested areas where on and off ramps of I-70 east of Russell.Most of those seemed to be people stopped coming off the interstate not really chasers.

 

[Robert S. Thompson]

I like the formula, I think it is well thought out. Maybe use the Day 2 1730Z SPC forecast to determine that portion of your equation as most people probably need to make the chase/no chase decision on Day 2 to schedule time off from work and/or travel. You could also add in a distance term: "0" if within X miles of previous day's highest risk area, "-1" is more than X miles from previous day's highest risk area. Not sure what value to use for X. RST

 

[Paul Knightley]

Surely the problem is that once you create an index, and publicise the formula, people will take this into account and perhaps start heading for an area when the CTI, meaning that you have to factor the CTI into itself to create a new CTI2 index, and so on....!

On a side note, on our 2 week 2 day 'chasecation' this year, we didn't encounter much chaser convergence at all really - some here and there, but nothing of much note.

 

[Dan Robinson]

Based on yesterday's high-traffic event between Quanah, Texas and Eldorado, Oklahoma caused by the limited bridge crossings of the Red River funneling most chasers onto Highway 6 and nearby secondary roads on either side of the river, I added a "road network" variable to the CTI formula:

http://stormhighway.com/blog2016/april2516a.php

 

[Jeff Duda]

I think you forgot June 7, 2009 in northwest Missouri. That was the first incidence I encountered with uncomfortably high chaser convergence. I'd say that qualifies as a CTI-6 or -7.

 

[Warren Faidley]

There also needs to to be desperation factor (DF), e.g., busy season with lots of storms vs. dead seasons when everyone is going to be out in very large numbers to chase the few good events.