Velocity of Falling Hailstones

[Tony Laubach]

I need some assistance in finding some information...

I am having a hard time finding a consistant number for the falling speed of hailstones. These are the five stones I am trying to find...

Penny, Quarter, Golfball, Baseball, Softball

If there's a chart/graph with this information that is freely available, that would be wonderful!

Thanks guys!

 

[Angie Norris]

Tony, the numbers I have are penny hail= terminal velocity of 35 mph, quarter hail = 50mph, golfball hail = 66mph, baseball hail = 85mph and softball hail = 117mph.
There was a chart somewhere in Stormtrack, but can't find it. It was either under library or links. My numbers are from a chart that Tim V produced a few years back, so I'd say they're pretty good values.

 

[Stan Rose]

Im sure you're aware, but for those who aren't, those numbers assume a perfect sphere of pure ice falling in standard unmoving air. A fair # of assumptions, since big hail often is pretty spongy and non-round, and it takes a strong updraft to form it in the first place (course wind-driven hail could increase the velocity beyond terminal)

 

[Jim Zandonai]

Actually Ironically I was interested in the same data but also for those same sizes of hailstones what kind of updraft speed is needed to keep the stones aloft ?

 

[Brian Stertz]

Yes those numbers are correct Angie...I've got some notes from back in the day at OU and these were the numbers for the various hailstones...of spherical solid structure. After seeing divots left by solid softball hail in the ground, I think that is very accurate velocity. I just always shudder to think of getting skulled by one. I've been hit by flat disc type 3" hail on the back and shoulder (Sept. 22, 2001) and that was like being hit with a baseball bat. Had some very deep bruises that lasted for about a week.

 

[Angie Norris]

From Eagleman's Severe and Unusual Weather, a 3 cm hailstone (~1.1" or slightly larger than quarter) requires an updraft of 100km/hr. An 8 cm hailstone (~3" or slightly larger than baseball) needs an updraft of 200km/hr. For the 10 cm variety (almost 4" or grapefruit) a 300km/hr updraft is needed. If I did the conversion correctly, that's ~62mph, ~124mph and ~186mph (if I didn't do the conversion correctly, please feel free to correct it )

 

[Robert Edmonds]

I ran through a quick a dirty approximation

Assume drag force is equal to -(1/2)*(air density)*(velocity)^2*(area)*(drag coefficient). Assume the hail is at terminal velocity(not accelerating), therefore drag is equal to -mg. Set equal and solve for velocity. Assume spherical with drag coefficient ~.47(note this can change with speed), air density at sea level, hail has typical density similar to ice. In the end I get...

speed of hail ~ 52.0*sqrt(size of hail in inches) mph. It's a approximation but pretty good.

note I changed the equation it was set for radius not diameter

 

[Tony Laubach]

Muchos Gracias, folks!