SPC Thunderstorm/Tornado Watch Verification Study - Part 1

[IndianaWxOnline]

Well first of all, it has been a long time since I have posted here, and figured I would start stopping by again!

Figured you guys might be interested in this study I just got done doing, and am still working on.

This is meant in no way to bash the SPC, but I am in the process of researching the verification rates and lead time for SPC issued tornado and severe thunderstorm watches. This first part of the study is concerning PDS Watches and in general the numbers of the different types of Watches issued this year. I have been curious all season with the PDS Watches as in my opinion I have felt that we have seen more and more PDS Watches being issued than normal, but I was sort of surprised to see that there have only been 10 as for some reason I had thought there had been more than that.

I considered the PDS Watch verified if one F2 tornado or higher occurred within the watch area, and out of the 10, only 5 verified. Here are the stats for part 1 of the study.

PDS Watches:

1. Tornado Watch # 5 Slight Risk Day (Missouri Jan 7th) Verified Issued by: Corfidi

2. Tornado Watch # 17 Slight Risk upgraded to Moderate (Much of the Mid-South January 10th) Verified Issued by: Hales

3. Tornado Watch # 36 Moderate upgraded to High (Arkansas Super Tuesday) Verified Issued by: Thompson

4. Tornado Watch # 37 Moderate upgraded to High (Much of Western Tenn, Kentucky, etc Super Tuesday) Verified Issued by: Thompson

5. Tornado Watch # 120 Moderate upgraded to High (Georgia and South Carolina March 15th) Verified Issued by: Hales

6. Tornado Watch # 130 Slight Risk (Arkansas and Northeast Texas March 18th) Not a single tornado report or strong tornado report - NOT VERIFIED Issued by: Hales

7. Tornado Watch # 131 Slight risk upgraded to Moderate Risk (Texas, Louisiana March 18th) 1 EF-0 Tornado, no strong tornadoees - NOT VERIFIED Issued by: Hales

8. Tornado Watch # 169 Slight risk upgraded to Moderate Risk downgraded to Slight Risk (Oklahoma & Northern Texas April 7th) 1 EF-0 Tornado, no strong tornadoes - NOT VERIFIED Issued by: Hales

9. Tornado Watch # 179 Moderate Risk (Texas) 1 EF-1 Tornado, no strong tornadoes - NOT VERIFIED Issued by: Hales

10. Tornado Watch # 180 Moderate Risk (Southern Oklahoma) 1 EF-0 Tornado, no strong tornadoes - NOT VERIFIED Issued by: Hales

Total PDS Tornado Watches issued: 10
Total PDS Tornado Watches Verified: 5
Total PDS Tornado Watches Not Verified: 5
Verification Rate of PDS Watches: 50%

Total Tornado Watches Issued This Year: 116
Total PDS Tornado Watches Issued This Year: 10
Total Severe Thunderstorm Watches Issued This Year: 76

It just has seemed like the once enhanced PDS status has been used more and more liberally, and while I know that has very little impact on the public, I was curious what the PDS verification rates looked like.

Part 2 is still a work in-progress which will hi-lite lead times and verifications of severe weather parameters within the watch area. Once again though, I think the folks at the SPC do a fine job, but was curious about the PDS Watches this year and just curious about the verification rates in general.

[CrazyC83]

IMO, a PDS watch verifies if it produces a significant tornado outbreak in the area - i.e. at least 10 tornadoes per 50,000 square miles (equivalent to Oklahoma without the Panhandle), of which at least 3 are F2/EF2 or greater OR at least 1 is F4/EF4 or greater.

Using that criteria though, the verification rates do not change.

As for a PDS Severe Thunderstorm Watch (which is very rare and has not been issued in 21 months), verification IMO requires at least 50 high-end wind reports in that same area (i.e. structural damage or measured 75 mph or greater), of which at least 10 are extreme reports (measured or damage-estimated 100 mph or greater) OR at least 3 are measured or damage-estimated 115 mph or greater.