SPC Watch Probability consistency

[Jeff Snyder]

For the SPC mets among us... I was wondering if there were set criteria for tornado vs. severe and PDS vs. "regular" watches when it comes to the watch probabilities. I ask this because I've seen severe thunderstorm watches when the "Probability of 2 or more tornadoes" was 20% (such as http://www.spc.noaa.gov/products/watch/ww0...prob.html]WW129), but now I see that Tornado Watch 167 has "Probability of 2 or more tornadoes" at 20% as well. I've also seen PDS watches with "Probability of 1 or more strong tornadoes" of 30% (like WT157), and non-PDS watches with "Probability of 1 or more strong tornadoes" of 40% (like WT155). I'm sure the size of the box plays a role in the type of watch for a given probability (or vise versa), since the size would affect the overall threat to any given location w/in that watch, and I'd think that a Tor box may be issued in those situations like "if there are any tornadoes, they may be strong or have a path length >2 miles" even though the overall threat is rather small. Regardless, the watches listed above aren't particularly small, so I don't think size directly affects those. IIRC, I saw a few cases last year with a severe watch, but with "Probability of two or more tornadoes" at 30%, higher than some tornado watches are comparable size.

At any rate, just curious if there are criteria, or if the probabilities and watch types are up to the individual meteorologists... Thanks!

 

[Rich Thompson]

For the SPC mets among us... I was wondering if there were set criteria for tornado vs. severe and PDS vs. "regular" watches when it comes to the watch probabilities. I ask this because I've seen severe thunderstorm watches when the "Probability of 2 or more tornadoes" was 20% (such as http://www.spc.noaa.gov/products/watch/ww0...prob.html]WW129), but now I see that Tornado Watch 167 has "Probability of 2 or more tornadoes" at 20% as well. I've also seen PDS watches with "Probability of 1 or more strong tornadoes" of 30% (like WT157), and non-PDS watches with "Probability of 1 or more strong tornadoes" of 40% (like WT155). I'm sure the size of the box plays a role in the type of watch for a given probability (or vise versa), since the size would affect the overall threat to any given location w/in that watch, and I'd think that a Tor box may be issued in those situations like "if there are any tornadoes, they may be strong or have a path length >2 miles" even though the overall threat is rather small. Regardless, the watches listed above aren't particularly small, so I don't think size directly affects those. IIRC, I saw a few cases last year with a severe watch, but with "Probability of two or more tornadoes" at 30%, higher than some tornado watches are comparable size.

At any rate, just curious if there are criteria, or if the probabilities and watch types are up to the individual meteorologists... Thanks!
[/b]

Jeff,

We are supposed to be consistent with the following guidelines:

1. Tornado Watch - minimum prob of 2+ tornadoes of 30%, unless going 20% with a 10% or greater prob of F2+.

2. Severe Watch - maximum prob of 2+ tornadoes of 20%, and a minimum prob of 6+ reports of 40%.

We do allow for "20%" tornado watches in the case where local offices really want tornado and we don't quite agree, but we issue tornado anyway. I can't say for sure what happened with TOR 157.

There's nothing to enforce consistency at the moment other than the forecasters themselves. In the next year or so, we'll likely make the wording and watch type internally consistent. The tricky part seems to be the PDS watches, which are driven by the outlook as much as anything. I'm guessing that we'll enforce some internal consistency with the PDS distinction in the next year. Personally, I'm not convinced that the PDS wording really means much, and it would be easier for me if we just didn't have that choice.

Rich T.

 

[Jonathan Whitehead]

Rich,
thank you for you comments on subject.
I agree with your comments on internal consistency b/c there does need to be at least a little bit more consistency in the WW's.
Secondly, I am a big fan of the PDS criteria that can be added to WW's. Unfortunately they've lost their emphasis and importance with not only the media but NOAA weather radio. The TORN watch that was issued for northern Oklahoma on 3/30 was PDS and my weather radio didnt even mention PDS in their first warning alert statement. Same thing for the eastern Oklahoma watch on 4/6 (I believe that was PDS). I just wish PDS was taken as seriously as it used to be in the 80s and 90s. I definately think SPC should keep with the PDS wording to WW's but should definately have hardline criteria for such issuence.

 

[Rick Smith]

Unless the watch is recorded manually for weather radio, the formatters that turn the text into speech will not recognize the watch as PDS.

 

[Damon Poole]

You're right about the PDS Watches on NOAA Weather Radio. I agree that the main problem has to do with the software that the NWR Console Replacement System uses to format those messages. You might have also noticed that they also simplified the "Remember...A Tornado (or Severe Thunderstorm) Watch means.." statement, too. I guess this was done to be generic and allow for the County Watch Notification alert to be shorter for use in the EAS, and, to air more quickly. Back in the day when humans did all the announcing, the PDS and the Remember statements were read verbatim right after the county list. I also am a PDS fan and hopefully when they release future updates to the CRS software, they'll allow for a little more flexability.

Damon Poole