Spooky sound (not thunder) in storm E. of Road 71, 12 mi N of Stoneham: What was it??

[Carol Sidofsky]

Yesterday (Thurs., July 14, 2011) my husband Dave and I were driving South on Colorado Road 71, and we were about 12 miles north of Stoneham, CO.

A big impressive storm was to our east--lots of rain & ?hail shafts and lighting & thunder.

Shortly before sunset, we got out of the van to stand in awe, watching that storm, and we thought we saw a little rotation in some clouds just to our east.

While watching, we heard a strange sound coming from that storm, that we had never heard from a storm before. The sound was a loud, low pitched, powerful, rumbling constant (no changes--was continuous) sound, kind of like a train, but it wasn't thunder. The sound lasted for what seemed a very long time. The sound seemed to be relatively close to us, but seemed to be coming from the other side of (? or within?) the rain curtains. It sounded fairly low to the ground. We were simply awe-struck!

Dave thought it must be a tornado, since he thought it had a wind-type sound to it. How far away does the sound of a tornado carry? Does that vary?

There was no train in that area.

What was that strange and awesome loud, low pitched, constant rumbling sound?

Did anyone else hear it, on Thursday evening in that severe thunderstorm (North of Ft. Morgan, CO)?

I called it in, and the meteorologist in Boulder said they were also watching that storm, which he said they were going to immediately warn as being severe (shortly before sunset), Did anyone else hear that spooky sound yesterday (Thurs. 7-14-11)??

After we got onto Road 52 heading south, there was no more sound, but the huge, pendant, mamatocumulous clouds were amazing to see, as they turned sunset colors, and had their shadows hitting the humongously big anvil, --from the low angled sun. What a sky!!

The meteorologist wondered if the sound was from hail, &/or from some updraft.

We're looking for answers about the sound.

Carol and Dave (from the Fraser area)
cell: 970-531-5000

 

[cstrunk]

I had a nearly identical experience probably 10 years ago or so while at home back in Iowa. It was for a rather small, yet severe warned thunderstorm that was drifting south towards our house. As it got closer I could hear the low, constant rumbling sound that you described. It sounded like a jet aircraft flying overhead. We experienced some dime sized hail minutes later.

If you ask me, it's the downdraft area with the hail/rain/wind making a whooshing noise. There must be some certain conditions that make it so pronounced at times from a distance.

 

[Jason Foster]

"It's the hail wroar"

;-) CDC (that one was for you)

Colorado has been putting out some serious hailers lately. Not having been there, but from your description and knowing was the storms have been doing, I'd make a pretty good bet that was it.

It often can't be heard when you are close to the storm due to higher intense winds creating more noise, but if you find a calm area, close enough to the storm, close to the hail core, and listen close...it often sounds like an airplane, but without the doppler effect of it flying by...like it was stuck overhead.

 

[Andy Jackson]

It was probably a hail roar. If the NWS was just warning it severe there probably wasn't a strong couplet so I'd make a safe assumption that it wasn't a tornado. With that said, I've heard both tornadoes and hail roars as well as some "jet" sounds I couldn't pinpoint the cause, I'd almost call it a shear roar if there is such a thing.

 

[Andy Wehrle]

I've heard a sound similar to what you describe emanating from several thunderstorm clouds, all of them severe, some tornadic (including the Stoughton, WI tornadic supercell of 8/18/2005).

 

[Greg Stumpf]

We've called that "hail roar" ever since I started chasing (25 years) and I hear it anywhere from 0-3 times per year. But so far, nobody has proven that the sound is from hail, but it always seems to emanate from aloft when you are situated under or near the BWER.

 

[Jason Foster]

We've called that "hail roar" ever since I started chasing (25 years) and I hear it anywhere from 0-3 times per year. But so far, nobody has proven that the sound is from hail, but it always seems to emanate from aloft when you are situated under or near the BWER.

I'm far from a scientist, but hail points to the most likely to cause the sound (at least one that I've heard). It's the only thing that is the level of mass in a storm and moves as fast as it does (when finally falling). But I would love to have a couple of good arguments against it. Perhaps a subject for someone to write a paper on. Isn't Blair doing a bit of hail research right now. Would be cool to have an excuse to give him a call. Haven't chatted in a while.

 

[JanelleHelling]

Agree with all the folks who identified hail roar. As a native of eastern Colorado, and longtime resident of Weld county, I know this sound happens with big hailers. If you are in a location to experience outflow, you can often identify the smell of crops upwind that are getting clobbered - especially onions and cabbage. At the practical level, when you can hear one of these coming, it's time to put vehicles and animals under shelter and go inside. In my experience, this sound happens with really BIG hail -- the kind that can kill cattle or take windows out of farm machinery. I'm not sure if the noise is generated by the hail impacting the ground or the interaction of ice chunks within the storm itself. The racket made by "ice cubes in a blender." Or maybe both?

 

[Greg Stumpf]

Agree with all the folks who identified hail roar. As a native of eastern Colorado, and longtime resident of Weld county, I know this sound happens with big hailers. If you are in a location to experience outflow, you can often identify the smell of crops upwind that are getting clobbered - especially onions and cabbage. At the practical level, when you can hear one of these coming, it's time to put vehicles and animals under shelter and go inside. In my experience, this sound happens with really BIG hail -- the kind that can kill cattle or take windows out of farm machinery. I'm not sure if the noise is generated by the hail impacting the ground or the interaction of ice chunks within the storm itself. The racket made by "ice cubes in a blender." Or maybe both?

The sound that I've always identified had its source overhead, so it was not an interaction of hail and objects on the ground.

 

[David Wolfson]

I've also heard hail roar several times in my limited chase experience. It got me pondering, and I'd like to propose a hypothesis for one or another of the many atmospheric physicists on this forum who might like to take this further. Just give me a mention for the idea if it proves out in peer-reviewed research .

Many, many years ago I did a high school science project that displayed the Von Karman vortex street phenomenon using a 2D water flume and indicator dye. The Von Karman Effect is where an object in a stream sheds regular vorticies in its wake. The frequency of the vorticies depends on the stream velocity, the cross-section of the object, and the Reynolds number of the configuration. Research has shown that the formation of the vortex street is inhibited by object geometries that diffuse the turbulence -- hence the cast spiral one sees in some vehicle-mounted radio antennas that serves to inhibit resonant vibration of the antenna caused by vortex shedding.

As Greg Stumpf says the "hail roar" seems to be a hydro-acoustical phenomenon emanating from aloft. It has a relatively low first-order frequency of 100Hz or less, characterized as more of a roaring that a rushing sound.

With this information in hand, and courtesy of the Wikipedia entry for the "Karman vortex street" plus the parallel finding from another hail discussion thread that the terminal velocity of hail in m/s is approximately 90d^0.5, where d is the diameter in m, the following formula for the frequency of the vortex shedding is derived, said to hold true for 250 < R < 20000:
f = (90/d^0.5) * 0.198 * (1- (19.7/R))

The formula is rather insensitive to the Reynolds number R, and 20000 is reportedly characteristic of a thrown fastball, so I think we're basically ok there and didn't get into the weeds for these scratchpad calculations. For R = 20000, at d=.025 (approx. 1"), f=112Hz; d=.05 (approx. 2"), f = 80Hz; at d=0.1 (approx. 4"), f=56Hz.

In order for an audible low frequency roar to be produced I suggest that there must be a degree of coherence or resonance to the phenomenon rather than random noise production. Here's where it gets interesting (and more conjectural) IMO.... Falling hailstones are distributed randomly within the volume. If one considers the vortex street in the wake of a hailstone like a short dragged vibrating string, falling hailstones would not tend to have coherent wakes. However hail suspended in the updraft vault one suspects would assume more of a uniform distribution and remain proximate for a relatively long time within a limited volume -- conditions that would be more conducive for acoustic resonance.

A frequency of 60Hz equates to a wavelength of around 5m and an xyz separation of around 8.5m between stones. 80Hz is around 3.75m wavelength and 6.4m separation. 112Hz is around 2.7m and 4.5m separation. These values appear to be reasonable for real-world conditions.

So in conclusion the hypothesis is that occasionally the combination of hailstone size distribution, hailstone surface roughness characteristics, updraft persistence and configuration, and hail density promote constructive resonance of the vortex wakes. FWIW.

 

[joel ewing]

Hail Roar. I've heard it perhaps 5 times in 25 years. I actually heard it again this June at the Nebraska / S. Dakota border. It was a tough little storm that was all by itself, with a cork-screwing and quickly shrinking updraft. The storm was non-tornadic, and very small in comparison to most storms that one would normally associate a roar with.
Now.....I've always wanted to ask this within StormTrack: Has anybody ever seen a storm "open up" (as in a mouth would open wide) and absolutely ROAR for a few seconds? What I'm describing is not associated with hail at all. I experienced this in Arizona, and it absolutely terrified me. It was definitely some type of exhale or expulsion....and it was extremely loud.

 

[KFackler]

The sound that I've always identified had its source overhead, so it was not an interaction of hail and objects on the ground.

There are several good YouTube videos out there that appear to have good sounding hail roars. This is the best one I could find.

http://www.youtube.com/watch?v=qm7Pe1OjYCY

What is interesting is in the description they say that this was taken before a defined hail core was observed, so this goes along with Greg as the hail seems to be suspended aloft at this time. It also does sound like an airplane flying low to the ground as Jason mentions.

I think some of the guys that took this video are members so it would be interesting to hear their thoughts.

 

[Andrew Herron]

Umm, 60Hz has a much longer wavelength than 5 meters. Consider the ham '2 meter' band is 144 MHz and 6 meters is 50 MHz. I think you mean that 60 Hz is about 5000000 meters, or 5000 km.

 

[David Wolfson]

Ummm, no, Andrew . The speed of sound waves in the troposphere is 300m/s, more or less. You're thinkin' 'bout electromagnetic waves....

 

[Dan Robinson]

I have heard the 'hail roar' several times in IL with storms that apparently were not producing hail, IE, just very heavy rain. I think that given a quiet, rural environment, an isolated heavy precip core close by will make perceptible noise.