A comparative study of hailstorms in Switzerland, Canada and South Africa

Abstract

A comparison of 5 to 20 years of qualitative and quantitative observations of hailfalls and hailstorms by three of the most active hail research groups in the world, shows very similar characteristics in a number of aspects of the hail phenomenon. The main similarities are that (a) the frequency of hailstorms decreases with increasing intensity, (b) the characteristics of hailstones (maximum size, number density) and hailswaths (length, surface area, energy) increase with increasing hailstorm intensity (i.e. lifetime, volume), (c) the single and multi-cellular type storms are most frequent, whereas the supercell is rare, (d) the hail flux is not constant but pulsating, (e) the spatial structure of large hailswath is not uniform but contains 'hailcores' and (f) the post embryonic trajectories of common hailstones are often simple and similar.A number of differences are also observed between some of the regions, the main ones being (a) the upper limit of intensity of the more severe storms, (b) the succession and scale of cells in the storm development and (c) the percentage of various embryo types.A major conclusion of this comparative study is that the severe hailstorms, which cause most of the damage, are exceptional and show little similarity in the three regions. For the more requent light and moderate damaging ones, the study suggests that dynamics may be the result of pulsating phenomena.

A radar‐based methodology for preparing a severe thunderstorm climatology in central Alberta

“…The aforementioned diurnal cycle is consistent with the findings of Kozak (1998), who reported that the frequency of cloud-toground lightning strikes increases rapidly after 15:00 LDT and reaches a maximum around 19:00 LDT, after which the strike frequency decreases rapidly. The above data also corroborate the findings of Admirat et al (1985), who noted that the peak in thunderstorm activity in Alberta typically occurs between 17:00 and 18:00 LDT. By comparison, Bellon and Zawadzki (2003) found that the peak for severe thunderstorm activity in the Montréal area occurs between 15:00 and 16:00 LDT.…”

The episodic occurrence of hail in central Alberta and the Highveld of South Africa: Research note

“…If all the hailstones were Ú 33 mm for Alberta (or Ú 30 mm for the Highveld), the day was categorized as a non-severe hail day. Comparison with measurements using aluminium hailpads suggests that the observers were reliable in identifying hail larger than 30 mm with an error margin of about 10% (Admirat et al, 1985). There was no bias in sizing the observed hailstones.…”

“…This is in contrast to the most intense Alberta storms, which form most frequently during the middle of the summertime (Wojtiw, 1975). In both regions, however, the most common time of day for severe weather is the late afternoon (Admirat et al, 1985).…”

A hail climatology of the greater Sydney area and New South Wales, Australia

“…In Colorado, large and giant hail peak in mid-summer (June and July), which is also the case for all hail in June for the southwest of France (Maddox et al, 1981;Dessens, 1986). A comparative study of hailstorms by Admirat et al (1985) reveals that the most active hail fall periods are during June and July in Switzerland and Canada, and in November in South Africa.…”