PDS SVR vs TOR watch?

[Angie Norris]

So, why did SPC go with a PDS SVR watch? What makes it different from a TOR watch, other than this is a straight line wind event? What is the criteria for a PDS SVR? Is it based on progged wind speed or forward speed of the system (of course wind speed is a factor of the forward speed)?
I hope somebody is getting vid of this critter as it moves through!!

MODS: I know this is probably more of a post for the advanced section, but I can't get in there for some reason

 

[Matthew Harding]

I am guessing it might be because SPC is not looking for a great quantity of EF2 and higher tornadoes, rather, they are looking for multiple reports of winds greater than 80 mph. I am not sure though. Maybe somebody from SPC can comment on what their exact criteria is for issuing PDS watches (both SVR and TOR).

 

[John Wetter]

What makes it different from a TOR watch, other than this is a straight line wind event?

You answered your own question. A TOR watch would be for tornadoes, and a PDS severe watch is for extremely damaging thunderstorms. Check out the probabilities for the two watches currently in effect and this will point you in the right direction. It's basically due to the high probability of high-end severe reports.

 

[Rich Thompson]

PDS Severe Thunderstorm Watches are normally reserved for rare cases where there is an ongoing, high-end damaging wind event, or such an event is likely soon. We often see brief tornadoes with these bowing systems, especially where they intersect and ride along stalled surface boundaries. I guess it ultimately comes down to forecaster judgement when choosing between the two.

The only other recent PDS SVR watches I recall were back on 5/8/2009 for SE KS/SW MO, and around Chicago on 8/4/08. In each case, there were several tornado reports with circulations along the leading edge of the bow echo, though I'm not as certain about what happened around SW MO with the multiple EF2 reports the morning of 5/8/2009. There were also damaging winds of 75-100 mph over much larger swaths than the tornado reports, so it gets tough to figure out which threat to emphasize. I also ran into the same concerns way back on 5/6/03 around Saint Louis with an intense MCS that contained clear supercell elements. I opted for a TOR watch in that case, but also tried to "play up" the damaging wind threat. I guess it comes down to which watch type will garner the appropriate response, assuming that can be known.

Rich T.

 

[Pete Smith]

I'm new to the forums here, so I may be wrong on this. However I have seemed to notice that the SPC reserves these PDS SVR watches for events where extremely damaging wind gusts greater than 90 mph are expected. I've seen many SVR watches of 80 mph that were not labeled PDS. So 90 mph seems to be their criteria.

I did notice a tornado watch earlier this year where the SPC was expecting 90mph wind gusts, but since the tornados were not expected to be strong long-tracked tornadoes, they did not issue a PDS TOR watch.

Also someone posted the two previous PDS SVR watches, but I also recall one from June of 2007 that included the Oklahoma City area for potential 90 mph winds gusts from an overnight derecho.

 

[Robert Dewey]

I also ran into the same concerns way back on 5/6/03 around Saint Louis with an intense MCS that contained clear supercell elements. I opted for a TOR watch in that case, but also tried to "play up" the damaging wind threat.

Rich, is there a limitation put on the wind estimations for a TOR watch? For example, in the case you mentioned, would it be possible to issue a non-PDS TOR but with "EXTREMELY DAMAGING THUNDERSTORMS WIND GUSTS TO 105MPH" verbiage?

EDIT: Actually, I think I might remember a TOR on May 31, 1998 (very large scale derecho with numerous +100MPH reports) having the 105MPH verbiage.

 

[Rich Thompson]

Rich, is there a limitation put on the wind estimations for a TOR watch? For example, in the case you mentioned, would it be possible to issue a non-PDS TOR but with "EXTREMELY DAMAGING THUNDERSTORMS WIND GUSTS TO 105MPH" verbiage?

EDIT: Actually, I think I might remember a TOR on May 31, 1998 (very large scale derecho with numerous +100MPH reports) having the 105MPH verbiage.

We have no limitation on the wind estimates for a TOR vs. SVR watch. The question often comes down to the relative effectiveness of using the "PDS" wording with a SVR watch, or going "normal" TOR and losing that wording.

 

[Darrin Rasberry]

We have no limitation on the wind estimates for a TOR vs. SVR watch. The question often comes down to the relative effectiveness of using the "PDS" wording with a SVR watch, or going "normal" TOR and losing that wording.

Incidentally, I saw the term "derecho" defined on Good Morning America some few days before the derecho that crushed the KS/MO/IL area last month. What about continuing a minicampaign to educate the meaning of such a system to the public, and maybe investingating a new type of watch for that system? With winds packed as high as a derecho has, I'd think such an establishment would have valid grounds upon which to stand.

 

[Karen Trammell]

Incidentally, I saw the term "derecho" defined on Good Morning America some few days before the derecho that crushed the KS/MO/IL area last month. What about continuing a minicampaign to educate the meaning of such a system to the public, and maybe investingating a new type of watch for that system? With winds packed as high as a derecho has, I'd think such an establishment would have valid grounds upon which to stand.

IMO, I don't think we need to make things more complicated for the public by introducing new terms, warnings, watches to their verbiage. Keep it simple, especially since there is a large segment of the population that doesn't "get" the current terminology...

 

[John Wetter]

IMO, I don't think we need to make things more complicated for the public by introducing new terms, warnings, watches to their verbiage. Keep it simple, especially since there is a large segment of the population that doesn't "get" the current terminology...

I'd agree with Karen. We don't need to look back any further than the assessment done for the Parkersburg, IA storm... Even EM's and local fire depts either didn't know there was a PDS watch in effect, or didn't know what that meant for them and that was a PDS TOR watch! Keep it simple. Let the high end nature come out in the text and let the media folks run with it.

 

[beaudodson]

I'd agree with Karen. We don't need to look back any further than the assessment done for the Parkersburg, IA storm... Even EM's and local fire depts either didn't know there was a PDS watch in effect, or didn't know what that meant for them and that was a PDS TOR watch! Keep it simple. Let the high end nature come out in the text and let the media folks run with it.

I like the enhanced wording in watches. I do think, however, that the public doesn't care. OEM does care - when they understand what it means. It is a fine balance - SPC trying to give us as much information as possible and SPC trying to make sure the public understand what is going on.

Psychology is becoming a bigger and bigger factor in how assessments are done on the public's reactions to these products. The Super Tuesday report is an excellent read.

PDS tornado watches are similar to tornado emergencies. Does the public understand these concepts?

 

[Chris Hayes]

I'm new to the forums here, so I may be wrong on this. However I have seemed to notice that the SPC reserves these PDS SVR watches for events where extremely damaging wind gusts greater than 90 mph are expected. I've seen many SVR watches of 80 mph that were not labeled PDS. So 90 mph seems to be their criteria.

I did notice a tornado watch earlier this year where the SPC was expecting 90mph wind gusts, but since the tornados were not expected to be strong long-tracked tornadoes, they did not issue a PDS TOR watch.

Also someone posted the two previous PDS SVR watches, but I also recall one from June of 2007 that included the Oklahoma City area for potential 90 mph winds gusts from an overnight derecho.

In May 2004 northern Ohio was put under a PDS severe thunderstorm watch for a bow echo that formed over Indiana and raced across the state. That watch was for winds of 80mph. I remember one in Oklahoma a few years back that was for 80mph winds also. However, most of the time they are for winds of 90mph+ One a few days ago was for winds of 105mph.

 

[Chris Hayes]

I'd agree with Karen. We don't need to look back any further than the assessment done for the Parkersburg, IA storm... Even EM's and local fire depts either didn't know there was a PDS watch in effect, or didn't know what that meant for them and that was a PDS TOR watch! Keep it simple. Let the high end nature come out in the text and let the media folks run with it.

I miss the good old days when NWS offices would announce a watch over the weather radio and say "This is a particularly dangerous situation (destructive tornadoes) or (Very damaging thunderstorm wind gusts). I'm not sure if OUN still does it or not. I know they used to be very good about it, but I havent chased in OUNs area during a PDS event since May 15, 2003 so I'm not sure. I would like all the NWS offices use the enhanced wording in their watch announcements though when a PDS watch is in effect. It might act as a trigger for the TV guys to make mention of it as well.

 

[Mike Gibson]

I like the enhanced wording in watches. I do think, however, that the public doesn't care. OEM does care - when they understand what it means. It is a fine balance - SPC trying to give us as much information as possible and SPC trying to make sure the public understand what is going on.

Psychology is becoming a bigger and bigger factor in how assessments are done on the public's reactions to these products. The Super Tuesday report is an excellent read.

PDS tornado watches are similar to tornado emergencies. Does the public understand these concepts?

I agree with Beau. I'd go further and suggest embedding predictable language and/or computer-friendly info (VTEC-like) in the text so that computer programs can reliably detect the significance and present it to users.

Mike

 

[John Wetter]

I agree with Beau. I'd go further and suggest embedding predictable language and/or computer-friendly info (VTEC-like) in the text so that computer programs can reliably detect the significance and present it to users.

That might be hard, but one area could be to grab the probabilistic output for the watches for better information on the threat?

John