Topic: Hailstorm Intensity Scale

[Harley Pearman]

HAILSTORM INTENSITY SCALE

Hello

Further to my readings on severe weather, I have recently come across the term 'Hailstorm Intensity Scale". It is a term used in the United States and is a table used to describe the size of hail events. I thought that it would be useful to add this scale to the Forum for reference as I have not heard of this scale being used here in Australia. It may come in use when describing hail events.
Figures are in inches but it is easy to convert to cm.

Hailstorm Intensity Scale - Table

Intensity     General Description / Damage caused                               Size of hail in inches

H0             None                                                                          0.2 to 0.4 (Pea size)
H1             Makes holes in leaves.                                                   0.2 to 0.8 (Marble size)
H2             Strips leaves from plants.                                               0.2 to 1.2 (Penny size)
H3             Breaks glass panels and can scrape paint.                         0.4 to 1.8 (Nickel size)
H4             Breaks windows, scrapes paint.                                       0.6 to 2.4 (Golf ball size)
H5             Breaks some roof tiles, dents cars, strips bark.                   0.8 to 3.0 (Tennis ball size)
H6             Breaks many roof tiles, damages roofs.                             1.2 to 3.9 (Baseball size)
H7             Shatters roofs, serious damage to cars.                            1.8 to 4.9 (Grapefruit size)
H8             Cracks concrete roofs, splits trees, injury to people.           2.4 to 5 (Softball size)
H9             Marks concrete walls, kills people, fells trees.                     3.2 to 5 (Softball size)
H10           Destroys wooden houses, damages brick homes, kills people. 4 to 7 (Volleyball size)     

For example, the recent 9 December 2007 hail event in Blacktown would have registered around H5 / H6 using this scale but no higher.
Whereas, the recent thunderstorm of Saturday 29 March 2008 over parts of Sydney would have sustained hail in the H0 range causing no damage.

From (Extreme Weather (Revised and updated) Christopher C Burt - 2007).

Trust this comes in handy when describing hail events.

Harley Pearman

[Jimmy Deguara]

Hi Harley,

Thanks for posting that information. Although we tend to develop an understanding of hail size from damage ourselves, it is good to have a verified system that is already in place. Interesting read!

Regards,

Jimmy Deguara

[Shaun Galman]

Hi guys,

I have been wondering about this hailstorm intensity scale idea for some time now and it is great to finally see that one has been in use, and no doubt, very effectively.

I would have thought that once hail reaches H4. Breaks windows, scrapes paint. 0.6 to 2.4 (Golf ball size) it would have gone under the "Injury to People" category, and be attached to each successive rating from there on? My grandmother had her hand badly cut & broken by a hail stone that was tennis ball size (H5 on the scale) during the 1999 severe hail storm that hit the Sydney area. She was at South Windsor when it hit and under the cover of a large shop front awning when it bounced up and hit her.

Q: How long has this scale been in use now?

Kindest regards,
Shauno

 

[Harley Pearman]

Hello

Shaun, I have done a little further research on this.

To answer your question, it is a scale devised by Tornado and Storm Research Organisation in England (Date not known) to rate the intensity of hailstorms. Hailstorms are rated on 2 factors under this scale being:-

a) The diameter of the stones.
b) The damage done.

The diameter is rated by a size code. The scale extends from H0 to H10 with its increments of intensity or damage potential related to hail size (distribution and maximum), texture, numbers, fall speed, speed of the storm, translation and strength of the accompanying wind.

It has been modified for various countries to reflect differences in building materials and types.

The international Hailstorm Intensity Scale recognises that hail size alone is insufficient to accurately categorise the intensity and damage potential of a hailstorm, especially towards the lower end of the scale. Additional information such as ground wind speed or the nature of the damage the hail caused would help to clarify the intensity of the event.

Example:- A walnut size hailstone with little or no wind may scar fruit and sever the stems of crops but will not break vertical glass and may be ranked as H2 or H3. However if accompanied by strong winds, the same size hail may smash many windows in a house and dent the bodywork of a car and thus it would be given a higher grading such as H5.

Evidence indicates that maximum hailstone size is the most important parameter relating to structural damage especially towards the more severe end of the scale. Hailstone shape is also important especially as the effective diameter of a non spheroidal specimen should ideally be an average of the co ordinates. Spiked or jagged hail can also increase some aspects of damage.

There are variations presented to suit the needs of different countries.

In Australia, Macquarie University (Division of Environmental and Life Sciences - Department of Physical Geography) introduced it in 1986 with some variations to suit Australia's conditions. Still has the H0 to H10 range but a size Code is provided and a description is given of its impact similar to that stated in the first post.

Given that I have only just come across it, it does suggest that it is not widely used in the general public.

Good web sites where versions can be found is

http://www.torro.org.uk/hsintens.htm

http://www.torro.org.uk/torro/severeweather/hailscale.php

Trust this helps

Harley Pearman

[Richary]

Interesting, though size alone is not necessarily an indicator of damage. Apart from the obvious one being how hard they fall (speed) which I am sure vaires from storm to storm, some hailstones are not necessarily solid balls of ice. Yes - the large round tennis ball size ones are obviously a problem. But I have seen some which may have been golf ball size but were actually a conglomeration of multiple smaller hailstones that had stuck together so obviously weren't as solid.

And in a recent storm we had pea size round ones, and 10 cent size flat ones falling at the same time. So what scale would you rate that? Obviously given the total lack of damage H0 would be appropriate, but if people took the larger size they could easily rate it to H3.

[Jimmy Deguara]

You know, I must hand it over the British when it comes to developing scales and research in general on severe weather.

Was not the supercell concept developed by a British scientist (Browning) and now this scale and the Torro scale for tornadoes. And they don't experience much in the way of these major severe weather events!

Regards,

Jimmy Deguara

[Shaun Galman]

Thanks for the explanation and links Harley, much appreciated!

I guess the (almost infinite) variables would factor into multiple ratings all depending on how precise you'd like to be and where you are on the globe? Nicely thought out for a "relatively new" scale though? Now all we need is one for how electrically active a storm is and we'll be set

I do agree with Jimmy about the British, they are definitely dedicated to their sciences!

Cheers guys,
Shauno       

[Harley Pearman]

Hello

I will add the "Australian Version" to this here because the Intensity Scale has further explanations and a CODE with diameter ranges and an Intensity Rating attached to the code.

It may address conditions where varying sizes fall but no damage occurs. It is more detailed and should address some of the questions raised where various hail sizes occur during the one event.

TORRO Hail Intensity Scale - Australian version

Intensity          Size Code      Description

H0                   1                 True hail of pea size but no damage.
H1                   2 - 3            Leaves holed and flower petals cut.
H2                   1 - 4            Leaves stripped from trees and plants, fruit and crops bruised and scarred.
H3                   2 - 5            A few panes in glasshouses smashed, skylights broken, wood fences scored
                                         paint scrapped of window ledges and vehicles, caravan body work dented,
                                         perspex roofing holed, canvas (tents) torn, stems, stems severed and seeds threshed.
H4                   3-6              Some house windows and or vehicle windscreens broken or cracked, glasshouses
                                         suffer extensive damage, some felt roofs pierced, paint scraped off walls and vehicles,
                                         some thin car bodywork visibly dented, branches broken from trees, unprotected birds
                                         and poultry killed and firm ground pitted.
H5                   4-7              Some roof slates and potter type type tiles are broken, many windows broken, plate
                                         glass roofs and reinforced glass windows cracked or broken, bodywork of most cars
                                         that are exposed visibly pitted, bodywork of light aircraft pitted, serious or fatal injuries to
                                         small animals, strips of bark torn from trees, woodwork pitted and splintered and large
                                         branches cut from trees.
H6                  5-8               Many roof slate and tiles except concrete tiles broken, shingles and thatch roofs breached,
                                         corrugated iron and some sheet metal roofs scored and a few holed, brick walls slighted pitted,
                                         wooden window frames broken away.
H7                  6-9               Slated, shingles and many roof tiles shattered, exposing rafters, metal roofing punctured,
                                         brick walls pitted, metal window frames broken away, bodywork of cars and light aircraft
                                         seriously damaged.
H8                  7-10             Concrete roof tiles cracked, sheet metal, slate, shingle and other tiled roofs destroyed,
                                         pavements and bodywork of commercial aircraft seriously damaged, small tree trunks split
                                         apart and people likely to suffer serious injury if in the open.
H9                  8-10             Concrete walls pitted, concrete roof tiles widely broken, walls of timber homes holed,
                                         larger tree trunks cut down, risk of death to people caught in the open.
H10                9-10              Wooden homes destroyed, brick homes suffer severe damage and people caught in the
                                         open are likely to be killed.

In addition the Australian version has a size code as follows:-

Size Code        Diameter            Description                                   Intensity rating

1                   5 - 10 mm          Peas                                             H0 to H2
2                   11 to 15 mm       Mothball, bean, hazelnut                   H0 to H3
3                   16 to 20 mm       Marble, cherry, small grape                H1 to H4
4                   21 to 30 mm       Large marble, large grape, walnut       H2 to H5
5                   31 to 45 mm       Chestnut, pigeon egg, golf ball         H3 to H6
6                   46 to 60 mm       Hens egg, small peach, small apple     H4 to H7
7                   61 to 80 mm       Large peach, large apple, tennis ball   H5 to H8
8                   81 to 100 mm     Orange, softball                              H6 to H9
9                   101 to 125 mm    Melon                                           H7 to H10
10                 125 mm or greater (Coconut)                                    H8 to H10

The Australian version is designed to accommodate the majority of windspeeds within which hail falls and the emphasis is placed on the likelihood that hail of a given size is likely to produce damage within a given range. Richary, I trust the Australian version answers your query and it is a good question raised. The Australian one appears to be better than the US one I originally posted here.

Harley Pearman   

     

[Peter J]

Hi Harley,

Based on that scale, the severe storm (possible tornado) event of Oct/Nov 1983 in Croydon/Mooroolbark/Mt Evelyn/Montrose (O/E Melb - Vic) region would have had hail at the H7 level of the scale - maybe a low H8 category - at least to my vivid and clear memory of the event - It did make these suburbs resemble a mortar attack / bomb site.

Big Pete

[Richary]

Thanks Harley. That expanded scale is probably more relevant to conditions here at least. Would definitely put the most recent one at H0 with no damage (except to some of the orb spiderwebs in the garden - so maybe I will rate it 0.5!). And would put the Sydney eastern suburbs storm in 1999 at about H7. Which caused quite enough damage I don't think we need to go any bigger!

I can't even begin to imagine a H10!