Increase in hail size for warning criteria

[Andrew Pritchard]

Just got this in an email from Chris Miller from ILX.

The NWS Central Region (which includes all of Illinois and Indiana) will most likely be making a change in criteria for severe hail from 3/4" in diameter and larger to 1" in diameter or larger.

With respect to thunderstorms which have, or are expected to have, hail of 3/4" to less than 1" (penny and nickel sized) and wind gusts of 45 to 55 mph, our office will be issuing Special Weather Statements for these storms.

The benefit of increasing the hail criteria up to 1" is that we estimate about 40% fewer Severe Thunderstorm Warnings. This has been tested in Kansas for the past 3 years or so, and the media, emergency managers and the public really like the change. Also, recent damage assessment studies indicated that it takes 1" or larger hail to produce damage to structures or autos.

To put this in an Illinois perspective, in the last 10 years there have been nearly 3,900 reports of 3/4" or larger hail. During the same time period, there have only been 1,800 reports of 1" or larger hail. This means that nearly 2,100 hail reports have been for penny or nickel sized hail alone! The hope is that increasing the criteria will lend more credence to the severity of the Severe Thunderstorm
Warning.

The tentative date for starting this is March 16, 2009 - but again that is tentative.

 

[Dustin Wilcox]

I was talking with a local forecaster for the NWS and as I have understood it the reason 3/4" hail demands a warning is more for aircraft than anything, in fact I think Offut (big AFB) takes action and issues warnings for 1/2" hail. Though I suspect as airline engineering quality like anything else increases over the years, eventually even planes won't be harmed by 3/4" hail...

 

[Scott Weberpal]

I got the exact e-mail from the WCM at MKX today. Is this an office to office thing or nationwide? The wording of the e-mail makes it sound almost like an office to office decision.

 

[Jason Harris]

What are the statistics connecting updraft strength and hail-size parameters? At what point do tornadoes become more likely based on those proportions? Often in warning texts you see claims about "any severe-warned storm can produce a tornado"--but what's the likelihood? Whatever it is, shouldn't that be part of what's taken into consideration with any reassessment of hail-size thresholds? Also wasn't the 3/4 inch hail size relevant for crop damage?

 

[John Wetter]

My understanding is that the whole CRH is looking into it after the test that has been ongoing in Kansas. I would sure hope it goes region-wide if they change it. And, I hope they decide soon!

 

[Brandon Ivey]

We have had the 1.00" standard for warning on hail in our area for a number of years. I really like the idea and hope it does go nationwide. It does cut down on the number of warnings. I would also like to see the wind criteria raised from 58mph to 65mph. We need to do away with some of these borderline warnings and not worry the public so much. That way when something is occuring that could really injure or kill them, they will be more likely to take the warning seriously. If they get 5 severe thunderstorm warnings for thier county that produce 3/4" hail and 58mph winds and then the 6th severe thunderstorm of the season rolls through with 4.00" hailstones and 80mph winds, do you think they will be ready to take shelter when that storm rolls through? They may be standing on thier porch watching it come in with their brand new truck sitting outside of the garage!

 

[Chris Bowman]

What are the statistics connecting updraft strength and hail-size parameters? At what point do tornadoes become more likely based on those proportions? Often in warning texts you see claims about "any severe-warned storm can produce a tornado"--but what's the likelihood? Whatever it is, shouldn't that be part of what's taken into consideration with any reassessment of hail-size thresholds? Also wasn't the 3/4 inch hail size relevant for crop damage?

This is a new issue that I haven't heard before. I'm not sure of any stats but I think what you're getting at is the larger the hail the more likely the storm is a supercell and therefore more likely to produce a tornado.

As far as crop damage that is a valid concern but there several factors to consider. One is if the hail is wind driven. In that case a SVR would still be issued. Two, the quantity of hail falling that essentially just beats crops down. I don't think you'll find much evidence of your average summer time thunderstorm doing much damage to crops. But suppose a farmer has a warning for 3/4" hail, what is he going to do? What possibly could he do to protect his crops? About the only thing he can do is have crop insurance.

The one inch hail criteria has been going on in Kansas for 3 years and has been a fantastic success. The media partners like it, the EMs like it and according to the media here they have gotten far fewer complaints from the public. Like maybe one or two.

Of course now I have to disclaim everything. So the thoughts posted in this reply are mine and don't necessarily represent the opinions of my employer.

 

[Chris Nuttall]

I got the exact e-mail from the WCM at MKX today. Is this an office to office thing or nationwide? The wording of the e-mail makes it sound almost like an office to office decision.

From the original post, it sounds like this is being implemented in all Central Region offices, but not nationally.

 

[Rich Thompson]

The "fun" part in all of this will be the watch program. I personally support raising the hail criterion to 1", but the national criteria for severe thunderstorm watches remain at an expectation of 6 or more occurrences of 3/4" hail and/or wind damage. You can literally face a situation where very few warnings are issued, yet there are more than enough 3/4" hail reports to justify a watch!

The integrated warning system will work better once we have consistency amongst all of the NWS regions. IMHO the best approach would be to reduce the number of marginal warnings and watches by raising the hail and wind criteria to levels more reflective of the actual threat to life and property.

Rich T.

 

[Shane Adams]

The "fun" part in all of this will be the watch program. I personally support raising the hail criterion to 1", but the national criteria for severe thunderstorm watches remain at an expectation of 6 or more occurrences of 3/4" hail and/or wind damage. You can literally face a situation where very few warnings are issued, yet there are more than enough 3/4" hail reports to justify a watch!

The integrated warning system will work better once we have consistency amongst all of the NWS regions. IMHO the best approach would be to reduce the number of marginal warnings and watches by raising the hail and wind criteria to levels more reflective of the actual threat to life and property.

Rich T.

I couldn't agree more. Needing to move your new car into the garage doesn't warrant a Severe Thunderstorm Warning IMO.

 

[Mike Johnston]

What are the statistics connecting updraft strength and hail-size parameters? At what point do tornadoes become more likely based on those proportions? Often in warning texts you see claims about "any severe-warned storm can produce a tornado"--but what's the likelihood? Whatever it is, shouldn't that be part of what's taken into consideration with any reassessment of hail-size thresholds? Also wasn't the 3/4 inch hail size relevant for crop damage?

Re: the mention of tornado possibility in SVR warning texts, it seems like including this is fairly situational. The offices do a pretty good job of adding this text when the overall situation is more conducive for tornado development, but by no means is it always included for every SVR warning - so I'm not sure that is necessarily an issue on the hail size parameter question.

Re: the test regions over the last 3 years, I could swear I heard in a spotter training class several years ago a forecaster from the KC/Pleasant Hill office mention that they were going with the change, so at least a portion of Missouri in addition to Kansas was included.

It would be interesting to compare the verification statistics, particularly the false alarm ratio, of the areas that have since changed the criteria to the national averages.

 

[rdale]

Re: the test regions over the last 3 years, I could swear I heard in a spotter training class several years ago a forecaster from the KC/Pleasant Hill office mention that they were going with the change, so at least a portion of Missouri in addition to Kansas was included.

I think any office that had Kansas responsibilities used it for their entire CWA - note the list at http://www.weather.gov/directives/sym/pd01005011c022006curr.pdf

 

[Rodney Price]

We've had this since 2005 locally. I'm happy to hear more offices will get this criteria. but do wish it were nationwide. I want to say the ICT office had a 20-30% reduction in the amount of warnings in their CWA in the first year of implementation (don't quote me on that exact stat though!). Sorry, I don't have more recent numbers.

Unless it is driven by extremely high winds (and then you'll have bigger issues on your hands) 3/4" hail is not going to hurt you or your car. Why warn for it then? "We're putting this scroll at the bottom of your screen (or worse yet...waking you up in the middle of the night) to tell you to do....absolutely nothing."

 

[Jeff Richardson]

The integrated warning system will work better once we have consistency amongst all of the NWS regions. IMHO the best approach would be to reduce the number of marginal warnings and watches by raising the hail and wind criteria to levels more reflective of the actual threat to life and property.

Rich T.

I'll second that...a million times. It would be impossible for me to count the number of times I've seen warnings issued for thunderstorms that barely met the "severe" criteria and posed little or no actual threat to life and property. For the sake of the folks at SPC, I hope the criteria for watches is revised as well.

Not to open another can of worms, but does anyone have thoughts/opinions on what are known as "Significant Weather Alerts"? For several years the Tulsa office issues those quite often for the run-of-the-mill thunderstorms so common in the warmer months. My concern is the public's perception of such an advisory/alert, confusing it with a warning, and getting into the "cry wolf" scenario.

 

[rdale]

The public rarely gets those direct from NWS - those are more intended for EMA's to give them a bit of a heads up.

When we in the media issue them, it's usually restricted to "storms we would want people to know about, regardless of the NWS issuing a warning." That usually means one we consider has stuff meeting severe criteria, or will be soon.

 

[Chris Nuttall]

I'll second that...a million times. It would be impossible for me to count the number of times I've seen warnings issued for thunderstorms that barely met the "severe" criteria and posed little or no actual threat to life and property. For the sake of the folks at SPC, I hope the criteria for watches is revised as well.

Not to open another can of worms, but does anyone have thoughts/opinions on what are known as "Significant Weather Alerts"? For several years the Tulsa office issues those quite often for the run-of-the-mill thunderstorms so common in the warmer months. My concern is the public's perception of such an advisory/alert, confusing it with a warning, and getting into the "cry wolf" scenario.

Those are issued in Southern Region offices. It's not specific to Tulsa.
http://www.nws.noaa.gov/directives/sym/pd01005017s052003curr.pdf

 

[Matt Gingery]

Personally, I think that warnings are issued for cells that are capable of producing severe weather. I understand that the entire warned area doesn't usually recieve the full impact of the cell, but sometimes it is difficult to tell where the FFD will be strongest so SPC does the best job that they can in order to cover all the bases. They have recently improved the area warnings as of late. Instead of issuing a warning for the entire county they issue it for the storm base track. In a cyclic cell the updraft is continuously overshooting the tops and being knocked down by the UA winds. As the updraft gets knocked down this sinking motion can produce severe winds and hail. The timing of this happening holds some uncertainty. A cell can produce 70mph winds in one area with large hail, and not match that level for 10 miles, but once the cell cycles again it will once again produce the severe level impact. SPC has many tools at their disposal, and I feel that they really do the best job that they can do with what they have to work with. It is the same with tornadoes in cyclic supercells, they issue the warning and if a tornado ropes out there is still strong rotation in most cases but not always confirmed touchdowns. I feel the warning is designed to warn the public of the potential hazards that should be expected, and in most cases severe weather usually occurs somewhere within the warned area, but not everywhere. Issuing watches is the area that I feel needs more research and development, i.e. convective outlooks, improving models. Given enough time and we always see improvement on a yearly basis.

 

[rdale]

SPC doesn't issue warnings - they do the watches. Local offices issue warnings. And you are correct - the goal is to issue for cells that will produce severe weather, but you can't always reach that goal. Sometimes the severe weather happens first.

 

[Jeff Richardson]

Those are issued in Southern Region offices. It's not specific to Tulsa.
http://www.nws.noaa.gov/directives/sym/pd01005017s052003curr.pdf

Thanks for the link, that was really informative. I've heard Significant Weather Alerts issued from other offices Southern Region offices in the past. Anyway, was just curious about those advisories and the reasoning behind them. That pdf file explained a lot to me. Thanks!

 

[Chris Bowman]

There are a few offices, at least, in Central Region that utilize the SWA for what they think is sub-severe. I have seen them issued as a "heads up" for a county before a warning would be needed. It's an effective tool for the offices that use them to say yeah that storm is out there, it's being monitored and if needed a warning will be issued.

The increase in hail size to one inch will really reduce the amount of warnings that are issued during pulse thunderstorm events unless the warning person feels that high winds are also a threat. I would have to double check as I don't have the numbers available readily, but I believe, and Rodney pointed this out, that Wichita issued something like 30 to 35% fewer warnings. This has resulted in warnings carrying more weight and the media doesn't need to cut into programing as much.

 

[rdale]

This has resulted in warnings carrying more weight

Is it that fast of a process? The public has ignored SVR's for years, and probably has no idea of the increased criteria. I don't think this is an instant sort of thing, it may be too late to catch their attention for a long time yet.

 

[Kiel Ortega]

While 1"+ hail for SVR warnings might decrease the number of warnings, I think it's important to remember that storm-based/polygon warnings have significantly increased the number of warnings (see below; apologies for the formating). Below are the warnings and verification for FY 2005-2008 in KS (wind speed in kts; penny means reports b/w 0.75 and 1 inch). FYI, 1" criteria were introduced during the FY 2006 (March 2006, I believe). I thought it was interesting that wind verification remained more or less the same even after the 1" criteria and polygon warnings were introduced. However, as you can see the introduction of polygon warnings (FY08), the # of warnings increased greatly. Also, you can see that penny-sized hail reports in KS remained the same (as I understand the directive, KS WFOs were to still collect penny reports), however the number of quarter+ reports nearly doubled. Really, I don't think there will be any significant impact in warnings from adopting 1" criteria, just an increase in # of 1" hail reports.


Year warnings penny hail quarter+ wind: 50 wind: 51 wind: 52 wind: 53 wind: 54 wind: 55 wind: 56+
2005 1559 513 880 27 7 223 7 5 19 320
2006 1667 517 816 19 5 256 13 1 12 440
2007 1299 405 643 24 5 185 7 2 4 218
2008 3192 573 1246 30 11 326 6 6 16 396

 

[Chance Hayes]

Many KS offices had already begun to issue polygon warnings or storm based warnings prior to 2008. I would chalk up the increase in number of warnings to a busier severe weather season. Though I won't argue that an increase in the number of warnings will occur, they will, just not by the amount depicted.

The increase in reports should also correlate with a busier season as well. The KS offices are still required to report any and all 3/4 inch reports that are received.

All posts and thoughts are mine and do not represent any agency or employer.

 

[Greg Stumpf]

Many KS offices had already begun to issue polygon warnings or storm based warnings prior to 2008.

But verification was still county-based during the test period (or so said my source at a CR WFO).

The increase in reports should also correlate with a busier season as well. The KS offices are still required to report any and all 3/4 inch reports that are received.

But there will be a lot less "huniting for dimes" since that will no longer be required to verify SVRs. Therefore, there will be fewer <1" reports. Will there be fewer reports overall? Unknown, as the "hunt" may be for nickels now.

All posts and thoughts are mine and do not represent any agency or employer.

Me too!

 

[Mike Smith]

As a Kansas meteorologist, far as I am concerned the 1" criteria has been a big success. Would like to see it nationwide.