BEHAVIOR PATTERNS OF NEW ENGLAND HAILSTORMS 
307 
TasiEe 1—Thunderstorm echo top characteristics 
Maximum hail size 
Parameter 
None (all rain) 
Height (K ft) 42 
37 
30 
Temperature (°C) —60 
—51 
—38 
Height above (+) or below +2 
(—) tropopause (Kx ft) —4 
—11 
Negative energy required for 9X, 10° 
tropopause penetration 0 
(ergs/gm of air) 0 
Diameter < 44” Diameter > 34” 
48 50 Upper quartile 
40 46 Median 
35 39 Lower quartile 
—60 —63 Upper quartile 
—54 —59 Median 
—48 —52 Lower quartile 
+5 +9 Upper quartile 
0 Fo) Median 
—6 +1 Lower quartile 
4.6 X 10° 1.4 X 107 Upper quartile 
0 6.3 X 105 | Median 
0 xX 105 | Lower quartile 
approach the conditions listed by Vonnegut and 
Moore [1958] for their category of ‘giant’ thun- 
derstorms. Their simplified assumption that the 
updraft speed at the tropopause equals 20 m/sec 
for each kilometer of penetration shows good 
agreement with a sample calculation. The re- 
quired updrafts are incredibly high for these few 
extremely penetrative storms. However, it is 
suggested later (under Hailstorm echo areas) 
that the first penetration of the tropopause ini- 
tiates a modification of the lower stratosphere, 
and hence the unreasonably high requirement 
for updraft speeds is considerably reduced. 
Composite hailstorm histories—Twenty  hail- 
storms depositing hail one-half inch or larger in 
diameter were selected from case studies con- 
ducted during the three years for examination of 
their common features, if any. A storm is defined 
as a unique radar echo, in most cases entirely sep- 
arate from other echoes at maximum radar re- 
ceiver gain and O° antenna elevation angle. Oc- 
casionally, the weaker, lower parts of a storm will 
merge with another storm, but the boundary be- 
comes clear at slightly reduced gain settings and 
especially at moderate heights (for example, 
above the melting level). A storm may have one 
to five or six well-defined echo cores which be- 
come visible from the surrounding background 
as the receiver gain is lowered. The cores, which 
are very likely related to convective cells, gen- 
erally have a much shorter lifetime than the total 
storm duration of two to six hours. 
Ten of the storms produced hail during a single 
period of less than 20 min, reported in every case 
but two from a single location. The others, named 
‘hail repeaters,’ dropped hail for periods of up to 
35 min continuously and up to 140 min inter- 
mittently. This classification of storm types may 
be analogous to that found by Douglas and 
Hitschfeld [1958] in Alberta hailstorms. They 
found that the hail usually fell in short bursts but 
on several occasions there were continuous hail 
falls of 1/2 hr in a swath 30 mi long. If the New 
England hail frequencies were increased by closer 
observer spacing (comparable to the tight Al- 
berta network) and by accounting for over-all 
regional differences in hail probability, some of 
our hail repeater storms might fill in to form 
continuous hail swaths. 
One further fact emerged: the single-hail pro- 
ducers ineluded no instance of severe wind dam- 
age (uprooting or fracturing of trees, structural 
damage to buildings, etc.). However, of the ten 
hail repeater storms, severe wind damage was re- 
ported in seven of them, including three storms 
with several tornadoes each and another one with 
two funnels aloft. Also, the maximum hail size 
was only 4 inch in four of the ten single-hail pro- 
ducers; hail of %4 inch diameter or larger was re- 
ported in all of the hail repeater storms. Inciden- 
tally, the maximum hail size in the repeaters 
appeared 10 to 100 min after the time of first hail, 
with a median separation of 40 min. 
In the analysis that follows, all times are given 
with respect to the first appearance of hail. This 
may be a dangerous thing to do because of 
the probable incompleteness of hail reports. Of 
course, the storm classification scheme is subject 
to the same criticism. However, for all its uncer- 
tainty, it seemed better to relate events to time 
