Changes to NWS Severe Thunderstorm Warnings (Adding Categories)

[Jeff Duda]

Much like what was done for impact-based tornado warnings several years ago, the NWS is rolling out a program to add levels of severity to Severe Thunderstorm Warnings starting later this year.

The essence is that SVR warnings will now have three levels of severity:

• BASE - standard warning issuance for minimal threat (60 mph wind/1 inch hail)
• CONSIDERABLE - wind gusts of 70 mph / hail of golfball size (1.75 inches) or larger
• DESTRUCTIVE - wind gusts of 80 mph or greater / hail of baseball size (2.75 inches) or larger

The highest category that either wind or hail threat meets will determine the tag of the warning. WEA alerts will not go out for BASE and CONSIDERABLE warnings...but only for DESTRUCTIVE warnings, to cut down on the false alarm and complacency problems from the public.

Full details: https://nws.weather.gov/products/PD...p6r3BSLm2dzjtpdK41XxYb85bxNXX3d0K_pFQS2q-mEQk

 

[Lou Ruh]

For these to be truly impact based, I think the criteria would need to include more possibilities. If 70mph winds go through an area where large trees are in residential areas (very common in the area I live in), 70mph winds are more than enough to bring trees down into houses ... into parts of the houses where folks should really get out of (like bedrooms) to save lives. I assisted with a storm survey in an area devastated by straight line winds estimated at 70mph and, the only reason there were no fatalities was the distant tornado warning (not affecting the surveyed area) that third party apps (from TV stations, etc.) sent to customers well outside of the tornado warned area. I would think another criterion that better represents the possible impact (potential level of damage, maybe) needs to be added ... otherwise, you could end up with no WEA message when you probably should have had one for the warned area.

 

[rdale]

There really is no way for a forecaster to know that 70mph winds in the north part of the city will cause deaths and in the south part won't... If that's the case - they'll just go 80...

If you look at StormData on wind deaths - 70mph winds don't really show up much. This is saving WEA for those truly deadly storms.

 

[Alex Elmore]

For these to be truly impact based, I think the criteria would need to include more possibilities. If 70mph winds go through an area where large trees are in residential areas (very common in the area I live in), 70mph winds are more than enough to bring trees down into houses ... into parts of the houses where folks should really get out of (like bedrooms) to save lives.

There's also no way of knowing exactly what is "beneath" a warning. Sub-severe winds can take down trees, branches, and light poles that are rotting. It's understood that 60, 70, and 80mph winds are *generally* going to produce certain thresholds of damage. Similarly with tornadoes, a well built home can brush off an EF1, whereas a mobile home that isn't strapped down will most likely get rolled. The latter could be considered catastrophic, but we can't use that tag on every warning or the point of the tag will be lost. Trying to create a warning with wording/criteria that cover every possible scenario is a losing battle.

 

[Lou Ruh]

There really is no way for a forecaster to know that 70mph winds in the north part of the city will cause deaths and in the south part won't... If that's the case - they'll just go 80...

If you look at StormData on wind deaths - 70mph winds don't really show up much. This is saving WEA for those truly deadly storms.

How widespread is the practice of NWS only surveying suspected tornadoes, and, a few cases where there is widespread damage? At least in my area, that is the case. So, I would suspect that most fatalities are UNK for the wind speed (but, I have not researched that). So, maybe not a good measure to go by (but, I guess there is not a better one at this point). I am waiting for StormData info on the June 3 derecho, but, there were four fatalities locally and no surveys were done. The survey I mentioned above was only done because of the tornado warning along with a good number of damage reports within the warning.

 

[Drew Terril]

I'm curious as to whether this is adding a layer of complexity from the standpoint of the non weather enthusiast. Considering I've been looking at weather related stuff since I was 6 years old, I don't have the frame of reference that someone who is in the general public would have, and whether this adds clutter or makes it easier to understand for the general population. What I can do though, is ask around with some of my non weather friends, and see what their thoughts are.

I've also crossposted to the ST Discord as well to get some additional awareness.

 

[Lou Ruh]

I'm curious as to whether this is adding a layer of complexity from the standpoint of the non weather enthusiast. Considering I've been looking at weather related stuff since I was 6 years old, I don't have the frame of reference that someone who is in the general public would have, and whether this adds clutter or makes it easier to understand for the general population. What I can do though, is ask around with some of my non weather friends, and see what their thoughts are.

I've also crossposted to the ST Discord as well to get some additional awareness.

Most likely, the non weather enthusiast is not looking that closely at how things are worded. Most folks I talk to just want to know if they are "safe", and, if not, should they do something. So, if they typically get that type of information from a WEA alert, they will now potentially get such an alert for severe thunderstorm warnings where that was not possible before.

 

[mkavulich]

WEA alerts will not go out for BASE and CONSIDERABLE warnings...but only for DESTRUCTIVE warnings, to cut down on the false alarm and complacency problems from the public.

I don't see in the product description document where they mention that WEAs will only go out with top-level warnings, is this covered somewhere else or do you just have internal knowledge?

If that change ends up being implemented I definitely agree with it, and I hope they do the same with flash flood warnings. IMO public complacency is big in this area. But I think to be most effective the changes need to be widely advertised for sure.

 

[Marc R. O'Leary]

How long before the weather channel starts naming severe thunderstorms and turns the word "DESTRUCTIVE!" into a regular everyday term for drizzly bird fart storms?

 

[rdale]

How widespread is the practice of NWS only surveying suspected tornadoes, and, a few cases where there is widespread damage?

Pretty widespread. There is no need to survey 60mph reports. That's what the local EM can do. But if there is 80+ winds, or deaths, I'm sure it gets surveyed.

I don't see in the product description document where they mention that WEAs will only go out with top-level warnings, is this covered somewhere else or do you just have internal knowledge?

That was in the PNS. The top level will be WEAd just like FFW tiers.

 

[Drew Terril]

Most likely, the non weather enthusiast is not looking that closely at how things are worded. Most folks I talk to just want to know if they are "safe", and, if not, should they do something. So, if they typically get that type of information from a WEA alert, they will now potentially get such an alert for severe thunderstorm warnings where that was not possible before.

That may be true, but we've long had an issue with the public not taking a severe warning (vs a tornado warning) seriously. Hence why I'm wondering whether this will make a discernible impact with communicating threats.

 

[rdale]

Hence why I'm wondering whether this will make a discernible impact with communicating threats.

Oh by all means yes... Apps can now safely ignore most SVRs and then trigger on the tag. Plus WEA is a big step forward.

 

[Alex Elmore]

So, I would suspect that most fatalities are UNK for the wind speed (but, I have not researched that). So, maybe not a good measure to go by (but, I guess there is not a better one at this point). I am waiting for StormData info on the June 3 derecho, but, there were four fatalities locally and no surveys were done.

Surveys are not done just because fatalities occur. Surveys are done to determine if damage was done by non-tornadic winds or a tornado, and if a tornado, what magnitude. If NWS meteorologists can easily determine through radar data what occurred, then a "in person" survey doesn't have to be done. If particularly significant damage occurs, regardless of fatalities, it may be surveyed even if meteorologists are confident in what caused it.

Looking over some of the fatalities from June 3 that are listed in the SPC reports, 3 deaths due to wind were because of trees falling on occupied vehicles. While tragic, trees can fall with 60mph winds or less, and vehicles are not going to hold up against a falling tree, so unless there's other significant damage in the area or a questionable feature on radar, that probably doesn't warrant a survey. Another death was because a tree fell on a power line that then fell on a house, causing the house to catch fire and kill an occupant. That is extraordinarily unlucky, but the fatality was indirectly caused by the wind, so it too probably doesn't warrant a survey.

 

[rdale]

Thanks for clarifying - I didn't realize he was speaking of trees being blown down. In that case yes a formal survey would not be necessary.

 

[Matt Zumbrunn]

Pretty widespread. There is no need to survey 60mph reports. That's what the local EM can do. But if there is 80+ winds, or deaths, I'm sure it gets surveyed.

We have taken winds in excess of 80 mph several times in the last few years. Ive never seen a survey team.