Vertical speed and hail

[David Shohami]

Does anyone know how fast the rising air in the updraft has to be in order to produce hail of a certain diameter? Let's say golfball size hail, for instance. Is there a chart perhaps for different hail sizes and vertical speed?
Thanks!

 

[Robert Dewey]

The equation for updraft speed (in meters per second) is:

The square root of ( CAPE * 2 ).

With that, a CAPE of 4000J/KG equates to roughly 89m/s in updraft speed. To me, that would be sufficient to maintain baseball sized hail (3 to 4 inches in diameter hail have terminal velocity of 40-60m/s, so it would take at least that to sustain them aloft).

 

[Michael P. Morris]

The only problem with that formula is that it neglects the effects of friction, water loading, turbulence, entrainment, etc. so it is really just an "ideal" measurement of the max updraft. A more accurate measure can be obtained by dividing the result from the equation by two. In the case of 4000 CAPE as mentioned, the maximum updraft speed would probably be around 50 m/s instead of 90. Still enough to sustain rather large hail, though.

 

[Robert Dewey]

The only problem with that formula is that it neglects the effects of friction, water loading, turbulence, entrainment, etc. so it is really just an "ideal" measurement of the max updraft. A more accurate measure can be obtained by dividing the result from the equation by two. In the case of 4000 CAPE as mentioned, the maximum updraft speed would probably be around 50 m/s instead of 90. Still enough to sustain rather large hail, though.

Yeah, that and there are some other ingredients as well, such as shear/wbz heights/freezing level/etc... I believe shear is one of the main components though - If it is weak, then chances are high that the storm will die before it even has the time to produce large hail, as opposed to a high shear environment with high CAPE, where the storm can persist several hours, with the hail growing in size as it recycles/remains aloft in the updraft...

 

[Jeff Snyder]

Reposting this since it fell victim to the server move...

Yes, while updraft strength is related to bouyancy (CAPE), it is also strongly affect by storm updraft organization and rotation. For example, given two storms in the same thermodynamic environment -- meaning the same CAPE, the same WBZ level, the same freezing level, etc -- two storms can have signficantly different updraft vertical velocities. A storm with a rotating updraft will have a stronger updraft, despite having available the same CAPE, than another storm without a mesocyclone. Strong vertical wind shear, presumably favoring updraft rotation, induces vertical perturbation pressure gradients, which enhances updraft velocity. So this is a very possible scenario: two storms, same environment -- completely different updraft strengths... Thus the reason why supercells, which have a rotating updraft by definition, produce the vast majority of very large hail, in contrast to the hail produced by other storm modes -- such as squall lines. Heck, a derecho ingesting 6000 CAPE air (the terminology isn't very good, but you understand) can fail to produce hail that a supercell ingesting lesser CAPE can produce (given the same wbz level, freezing level, etc)...

 

[David Shohami]

Thank you for the answers.
What I was trying to find out is something like this (the one-before-last paragraph):
http://www.erh.noaa.gov/box/updraft.html
dime=37mph
golfball=56mph
>baseball=100mph
etc etc.