2008 Moderate/High Risk Day - Verification

[beaudodson]

Several people have stated that the moderate/high risk days have underperformed so far this season. I think the outlooks, for the most part, look pretty good.

Three risk categories (SLGT, MDT, and HIGH) are used to symbolize the coverage and intensity of the expected severe weather threat.

A SLGT risk implies well-organized severe thunderstorms are expected, but in small numbers and/or low coverage. Depending on the size of the area, approximately 5-25 reports of ¾ inch of larger hail, and/or 5-25 wind events, and/or 1-5 tornadoes would be possible.

A MDT risk indicates a potential for a greater concentration of severe thunderstorms than the slight risk, and in most situations, greater magnitude of the severe weather.

A HIGH risk area suggests a major severe weather outbreak is expected, with a high concentration of severe weather reports and an enhanced likelihood of extreme severe (i.e., violent tornadoes or very damaging convective wind events occurring across a large area). In a high risk, the potential exists for 20 or more tornadoes, some possibly F2 or stronger, or an extreme derecho potentially causing widespread wind damage and higher end wind gusts (80+ mph) that may result in structural damage.

A SEE TEXT label will be used for areas where a 5% probability of severe is forecast, but the coverage or intensity is not expected to be sufficient for a slight risk.


Here are all of the moderate/high risk days for 2008.

http://www.usawx.com/2008spcforecast.htm

 

[Shane Adams]

The biggest misconception with enthusiasts and even chasers regarding SPC outlooks continues to be they think of them in terms of chasing instead of serving the general public.

 

[Dustin Wilcox]

Looking through the link you provided, I would say if one looks at it from a perspective other than being a chaser looking for tornadoes, the outlooks have been quite justified and in the end verified, with maybe one exception, this past Thursday.

 

[rdale]

I'd like to see a PDS watch box compilation like the above...

 

[beaudodson]

I added the PDS boxes.

 

[Tim Shriver]

Here is Wisconsin last year we had a high risk that the press jumped all over
when very little happened.

I say that it’s like a semi-truck full of dynamite coming through town, just
because it didn’t blow up doesn’t mean the danger was not present.

I think over all the SPC does well. But just like all of us, they miss the mark now and then.

Tim

 

[Mikey Gribble]

I don't think they've done too bad on the categorical outlook (hail and wind seemed to verify alright), but the tornado probabilities haven't verified very well this year. You have to cut those SPC guys some slack though. They are forecasting for public safety and because of this they have to error on the side of caution IMO. We have had four or five days where one or two ingredients were mitigating the tornado threat. In all those cases we were teetering on the threshold of strong torndaoes. High tornado probabilities were issued on each of these days and they didn't verify, but when it's close you better cover your ass IMO. There are no consequences for us when we botch a forecast so we can say exactly what we think will happen, but forecasting for the public is a completely different situation. That being said I think they shouldn't have issued high tornado probabilities for the two veering low-level wind moderate days, but they did. I actually agree with them going with high tornado probs on Wednesday and Thursday of this week. There were a couple question marks on each day and a couple mitigating factors as well (for tornado potential), but high 1km SRH in both cases could have created an environment favorable for strong tornadoes. Both days were tough forecasts and I didn't think the tornado probs would verify, but I still agreed with the categorical outlook and tornado probs. I guess what I'm trying to say is that the potential was there on both days this week and although I thought the chances for a tornado outbreak were low, they have a responsibility to error on the side of caution.

 

[beaudodson]

Just to be clear - I posted this to show that the SPC has done well with their outlooks. There has been a lot of discussion on this topic lately. I suppose one could argue that the PDS boxes have not lived up to their name - for the most part. I am not sure anyone cares about that? Nobody that I know even realizes that they are in a PDS box vs a regular tornado watch (and I have asked around). The only people who seem to care about this subject are storm chases, weather enthusiasts, and those interested in meteorology.

On another note:

More importantly, to the public, is the fact that all tornado deaths, with the exception of one, this year were inside of a watch box or close to a watch. That in itself it worth noting. I know the "risk outlooks" are important but the watches and warnings are MOST important to the public.

Stats for tornado deaths vs watches

http://kamala.cod.edu/SPC/latest.nwus23.KWNS.html

 

[Mikey Gribble]

They shouldn't IMO hoist high tornado probs when there are veering low-level winds in the plains. I honestly can't remember a single setup since I started chasing where we had good tornadoes when low-level winds were veering. On the other hand I got suckered into chasing on one of these days, so I guess I'm just as guilty as they are.

 

[rdale]

I am not sure anyone cares about that? Nobody that I know even realizes that they are in a PDS box vs a regular tornado watch (and I have asked around). The only people who seem to care about this subject are storm chases, weather enthusiasts, and those interested in meteorology.

Actually many in EM step up their coverage and response when in a PDS watch. And many TV weathercasters (not mets) also go the extra mile in hyping an event when PDS is in the text too... So "Joe Public" certainly won't know, but many others will use that information.

I highly despise clear-air PDS watches. "Back in the day" when it took an hour to coordinate everyone involved, issue the prelim lat/long, get counties in/out, etc. it was different. But now it can be just minutes from the time you decide to issue a watch before it's out, so in conditional cases I'd rather see "the reds of their dbZ's" before going full bore PDS.

That "restriction" would have reduced the number of PDS's, maybe even reduce the number of blue sky busts.

 

[Mike Smith]

I, too, believe there are too many PDS watches while PDS are not issued in cases where they are clearly needed (i.e., May 4, 2007 -- Greensburg).

I believe that PDS watches need to be refocused on the (infrequent) situation where we believe F4 or F5 intensity tornadoes are possible or likely. As I understand it, a PDS watch currently verifies if there are two or more tornadoes of F2 or greater intensity.

 

[Mikey Gribble]

It doesn't seem like there are a whole lot of PDS's being issued. I agree on the Greensburg comment Mike made. There absolutely should have been a PDS watch that day. Conditions were perfect for tornadoes and even the day before it was evident violent tornadoes were possible if storms fired along the dryline bulge. I have no idea why they didn't issue one then.
With the current criteria for PDS watches, I don't think they did anything wrong issuing the last two (I think it was Monday and Wednesday). Both days might have been able to produce F2's. I thought Monday was a slightly better setup, but aside from a lack of insolation on Wednesday it wasn't bad either. This is another example of everything being in place minus one or two things for strong tornadoes. IMO you have to error on the side of caution in these cases if you're SPC. I also agree with the idea that maybe they could go with a regular watch and then upgrade that watch to a PDS (if that is what was being inferred) once the event begins to unfold.

 

[beaudodson]

Actually many in EM step up their coverage and response when in a PDS watch. And many TV weathercasters (not mets) also go the extra mile in hyping an event when PDS is in the text too... So "Joe Public" certainly won't know, but many others will use that information.

I highly despise clear-air PDS watches. "Back in the day" when it took an hour to coordinate everyone involved, issue the prelim lat/long, get counties in/out, etc. it was different. But now it can be just minutes from the time you decide to issue a watch before it's out, so in conditional cases I'd rather see "the reds of their dbZ's" before going full bore PDS.

That "restriction" would have reduced the number of PDS's, maybe even reduce the number of blue sky busts.

I meant in the public. They don't care.

Our local station has a set of rules:

Slight risk - they have X people on duty
Moderate risk - they have X people on duty
High risk - they have full staff.

They don't care if a tornado watch is a PDS box or not. I have learned over the years that a tornado watch is a tornado watch. Some produce more tornadoes than others. Some will produce no tornadoes. Each watch should be taken seriously.

As far as emergency management - a moderate or high risk will have my attention more than a slight. A PDS box will heighten my own interest but most of our spotters and others don't care.

I personally don't care for PDS watches. That is just me though. I know that has been debated on the forum before.

 

[beaudodson]

I, too, believe there are too many PDS watches while PDS are not issued in cases where they are clearly needed (i.e., May 4, 2007 -- Greensburg).

I believe that PDS watches need to be refocused on the (infrequent) situation where we believe F4 or F5 intensity tornadoes are possible or likely. As I understand it, a PDS watch currently verifies if there are two or more tornadoes of F2 or greater intensity.

Here is a verification thread on the PDS watches

http://www.easternuswx.com/bb/index.php?showtopic=162235