PDS SVR vs TOR watch?

[Paul Knightley]

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.

Rich - I hope you don't mind me asking this...in SVR and TOR watches, are the wind speed estimates based on possible RFD velocities, FFD velocities, or a mixture?

From my experience with issuing experimental forecasts for the UK it's pretty tough to nail them all the time!

 

[Rich Thompson]

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

We are now testing specific wording at the beginning of the public watch product (SEL) that is driven specifically by the watch probabilities. They should become available on the web page soon, but I don't recall the specific date.

This new wording will list the threats in order of significance based on expected coverage and intensity of tornadoes, damaging wind, and hail.

Rich T.

 

[Rich Thompson]

Rich - I hope you don't mind me asking this...in SVR and TOR watches, are the wind speed estimates based on possible RFD velocities, FFD velocities, or a mixture?

From my experience with issuing experimental forecasts for the UK it's pretty tough to nail them all the time!

Paul,

The wind speed estimates are not specifically for the RFD or FFD areas of a storm. The RFD can be especially tricky since it gets difficult to separate it from a tornado circulation. The wind estimates are notoriously hard to nail down because thunderstorm winds are usually not measured consistently outside of the larger convective systems passing through areas like the OK mesonet.

The wind numbers we put on the watch are essentially a best-guess for the stronger (but still somewhat common) gusts to be expected within the watch area.

Rich T.

 

[Paul Knightley]

OK, thanks Rich. In my experience in the UK it's often easier to estimate wind gusts in convection when we have some strong low-level shear to work with (e.g. a line squall on a strong winter cold front, with a powerful 850 hPa LLJ just ahead of it) compared with a summertime situation with plentiful moisture/CAPE, and marginal shear (when perhaps a small cluster/MCS develops, and produces severe wind damage).

 

[Pete Smith]

Okay, we now have a PDS SVR in effect for parts of Kentucky, Tennessee and Georgia until 7 PM EDT tonight for t-storm wind gusts of 80 mph. I've seen numerous SVR's for that wind criteria that were not PDS. What gives here? Why a PDS on this one and not others that contain similar wording?

 

[Mike Smith]

I had an email exchange with Joe Schaefer after the KS-MO-KY derecho earlier this spring. I noticed the PDS severe thunderstorm watch called for 80 mph winds but the non-PDS tornado watch called for 105 mph winds. That didn't make sense to me.

Joe agreed and said they would address it after the season was over.

 

[Pete Smith]

I had an email exchange with Joe Schaefer after the KS-MO-KY derecho earlier this spring. I noticed the PDS severe thunderstorm watch called for 80 mph winds but the non-PDS tornado watch called for 105 mph winds. That didn't make sense to me.

Joe agreed and said they would address it after the season was over.

I was thinking the same thing. I remember that "non-PDS" tornado watch from earlier this year and was thinking that they need some more forceful wording for situations like that. The threat for long tracked destructive tornadoes may not have existed, but the threat for widespread EF1 type wind damage was there and really needed to be emphasized more. It will be interesting to see how this is addressed after the season is finished.

Back to the PDS SVR criteria though, I notice that most if not all of the recent PDS SVR's have been issued for 90+ mph winds but not for 80 mph winds. Unless this is a new criteria that is just now being enforced, it seems like the SPC does not follow the 80 mph criteria. Just wondering if this was very recently changed or whether they will now enforce the 80 mph criteria more.

 

[Mike Smith]

It is my opinion that the whole "enhanced wording" set of products should rethought. For more, see the "tornado emergency" thread that I reactivated today at: http://stormtrack.org/forum/showthread.php?t=12361&page=18