| Author | Message | ||
     Sifo |
Perhaps our resident meteorologist could explain something. What's the difference between a dust devil and a tornado? Is it just the wind speed or is there a difference in how they are formed? A couple of days ago crossing NV I went right through one. Pretty harsh sudden changes of direction! A bit later we saw another one where you could see a very well developed funnel that was white with vapor like you get with a tornado. I didn't know dust devils did this. The funnel went up probably 150 yards or so then went horizontal for a ways then went up some more. It was nice clear blue skies when this happened. Today we saw another with the vapor showing the funnel all the way up to a big rain cloud. This one could easily have passed as a small tornado IMO. Cool stuff to see when it's out in the middle of nowhere! | ||
| Geforce |
In Afghanistan we had dust devils strong enough to flip anchored tents over. I think the primary difference between the two is the hot/cold forces needed to generate wind speed. A tornado forms when warm/cool air collide. A dust devil occurs when air mixes at low ground levels absent of a warm/cold front. Pretty sure the difference is quite staggering considering I have been very close to both before and I'd take those massive 1000 foot tall Afghani tent crashers any day. | ||
| Aesquire |
I generally sort them into clear day/thermal/hot air rising/dust devil & Storm/supercell/tornado. Based on cause. A dust devil is a thermal column of hot air that, in rising, picks up rotation through local irregularities and coriolis force. Transient and sometimes quite strong. Clear blue sky dust devils are quite common. A tornado is a phenom of thunderstorms where large cloud internal thermal/rotating movement gets you a whirlwind going. Varies in size quite a bit up to "finger of G-d". "Cow" "'Nother cow" "Actually I think that was the same one." Waterspouts seem to be either. Big ones are tornados, little ones are thermal/dust devil style. Born and raised in tornado country, have flown through, and used dust devils in a glider & hang glider, and you couldn't get me near a tornado outside a tank or a bunker. you also get small transient dust/snow devils near corners of buildings, courtyards, etc. That's just a shedding vortex, though, and not the real heat pumped deal. http://en.wikipedia.org/wiki/Dust_devil http://en.wikipedia.org/wiki/Whirlwind http://en.wikipedia.org/wiki/Tornado http://en.wikipedia.org/wiki/Coriolis_effect | ||
| Sifo |
Pretty much what I thought. I just never saw dust devils back home with enough force to show the funnel by pulling vapor from the air. I have seen "the finger of God" type tornado. Actually had our car hit with debris from it traveling I80 out in Wyoming. There was no mistaking that for a dust devil. The problem with that one was that with all the crap thrown into the air a couple of miles wide, it hid most of the funnel from view. | ||
| Xl1200r |
Sounds like, in layman's terms, a tornado is caused by a storm and forms from the top down where as a dust devil is just caused by heat and starts at ground level. I live in upstate NY, and believe it or not we get both around here. I think it was about 12 years ago we had a strong F4, bordering F5 roll through and caused a lot greif. | ||
| Aesquire |
You guys pretty much got it.  | ||
| Sifo |
I'm still kind of wondering how powerful a dust devil can get. The one I rode through knocked the bike around quite a bit, but at 80 mph I was through it far faster than I could react. I was glad that I had a split second to brace myself before hitting it though. the stronger ones I saw where you could see vapor defining the funnel would really worry me. There must be some meteorological data on these. Know anything offhand? | ||
| Aesquire |
Personal experience includes gliders and light planes being picked up and spun about. But those are built to ride/modify airflow, and are relatively light. ( large surface area, low mass ) Most of those devils didn't have more than momentary condensation streaks. Depends on humidity if you can see those at a given pressure drop. Solid condensation in a whirlwind is a bit scary. Heard tales of jeeps spun around, and the south western ones tend bigger. Anecdotes for Effects up to tipping vans over, so, yeah, a bike can get pushed around a lot. Then there's gust front winds. That's where the initial rush of falling rain from a cloud that just got "tripped" and cut loose, push/drag a large air mass down, which splashes on the ground and races outward at high relative pressure and speed. Easily tip Semi's and throw motorcycles off the road. 90+ mph winds. Transitory, brief, but powerful. I've seen that from above, tree branches and crops look like ripples in a pond after a rock gets tossed in. Now, I'm a coward, so I try and avoid driving through anything opaque. ( with the right gear, some clouds...ok, unless there is granite inside. ) | ||
| Ourdee |
When I lived in NV I used to Chase them down on my bike and ride inside them. Incredibly calm in there. |
