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Here are some numbers for those of you who are interested in
the how much "punch" a hailstone has. Values here are for freefall only. You'd
have to increase/decrease it for wind effects. This was posted by Tim Marshall on
the U.S. chase listserver.
| Hail Size (IN) |
Freefall Velocity
KPH (MPH) |
Freefall Energy (FT-LBS) |
|
|
|
| 1/2 |
55.8
(34.7) |
.009 |
| 3/4 |
68.1
(42.3) |
.044 |
| 1 |
80.1
(49.8) |
1.43 |
| 1.25 |
90.0
(55.9) |
3.53 |
| 1.50 |
98.8
(61.4) |
7.35 |
| 1.75 |
106.5
(66.2) |
13.56 |
| 2 |
115.2
(71.6) |
23.71 |
Thus, a 1.25 inch hailstone has about 2.5x the punch of a one inch hailstone and a 2 inch
hailstone has about 17x the punch of a one inch hailstone. OUCH! The rapid increase in
freefall energy causes a sharp damage threshold for most roofing and siding products as
well as vehicle metal. This occurs in the 1 to 1.5 inch diameter range. Keep in mind that
hail will fall at different velocities due to its shape, density, spin axis, collisions
with other stones, etc. Small hail tends to "float" due
to air resistance. Rainfall
Information
Every wonder how we get the terms regarding rain and rainfall
rates. This chart should explain it all.
|
Drops Per sq. ft. per sec. |
Diameter of Drops (mm) |
Intensity (cm. per hr.) |
Intensity (in. per hr.) |
| Cloudburst |
113 |
2.85 |
10.24 |
4.00 |
| Excessive Rain |
76 |
2.40 |
4.01 |
1.60 |
| Heavy Rain |
46 |
2.05 |
1.54 |
.60 |
| Moderate Rain |
46 |
1.60 |
0.38 |
.15 |
| Light Rain |
26 |
1.24 |
0.10 |
.04 |
| Drizzle |
14 |
.96 |
0.025 |
.01 |
| Mist |
2,510 |
.10 |
0.018 |
.002 |
| Fog |
6,264,000 |
.01 |
0.012 |
.005 |
Here's a great little trick sent to me by Sandy:
Keep a small mirror in your instrument screen or other sheltered outdoor
space so that it'll be at ambient temperature. Expose it to the sky for
half a minute or so. One mm is the threshold between drizzle and rain. The
mirror also helps to distinguish hail, ice pellets, snow grains, and
freezing precipitation.
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