Ok guys, I’ve been following severe weather >for a while in my short life. I’m definitely not a pro so I apologize in >advance if this seems “stupidâ€.
>Is there any direct correlation with tornado intensity or tornado >frequency with outflow boundaries? I noticed discussion in the historic >chase event thread of 3/13/90 and Hesston that the storm was aided >immensely by an outflow boundary. I think the Andover tornado spun up >on one too maybe? How often do outflow boundaries lead into the >formation of tornadoes?
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I can't really give you a number or a percentage, and I'm not familiar with any outflow boundary help on the Hesston and Andover days. Perhaps the best way to approach this is to think of (most) tornadoes as rather small and fragile by-products of its "mother" cell or storm system. Conditions in the lowest levels of the atmosphere (say, from the surface to a couple of thousand feet up) need to be VERY favorable for tornado formation ---- even for tornado formation beneath supercells. A balancing act of sorts among the temperature, moisture, and wind fields in and around a storm is necessary in order for a tornado to form and to persist.
Some outflow boundaries --- some new ones and some old ones --- tend to be locales where the low-level "meteorology" can greatly enhance tornado development.
So the best answer to your question so far is --- "it depends". It depends on the outflow boundary and whether it is a good boundary or a poor boundary for tornado-making.
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> Is there a better a chance a violent tornado can form on one of those as >opposed to some other kind of a boundary?
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The answer to this one is a shaky "yes." From my experience, on the big days and outbreak days with numerous strong-to-violent tornadoes, outflow boundaries are of little or no consequence. If the atmosphere wants to make violent tornadoes, then it doesn't need a boundary. Outflow boundaries can be well-suited for tornado-making if they are oriented somewhat parallel with the mean flow aloft, allowing storms to "latch on" and ride the boundary. The same is true on occasion for warm fronts. Cold fronts and dry lines are "boundaries" which are often good for storm development, but tornadic storms tend to move off of these types of boundaries, so that it is not the boundary itself which aids in tornado formation. So, chasers playing the dry line or cold front don't sit right on the boundary and hope for tornadoes, whereas a chaser could position himself or herself on the warm front or outflow boundary to improve tornado-intercepting odds.
Outflow boundaries tend to be more important on the "subtle" slight-risk days when the overall synoptics are favorable for supercells (if storms can form), but the overall low-level regime is weak or generally unfavorable for tornadoes. However, an outflow boudary in this situation could well be the difference-maker in locally providing a very favorable environment for tornadoes. In addition, the boundary may also be where convective development is most likely, given the local low-level convergence. The May 24, 2008 event in northern Oklahoma (pig farm tornado) comes to mind. So, outflow boundaries can aid in storm development AND tornado formation.
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>Is there any difference with structure or formation when a tornadic >supercell forms on an outflow like Andover as opposed to say like the Red >Rock storm (which I’m assuming wasn’t formed on one?)
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Again, I don't know the role that outflow boundaries played on this day (my guess is that they were of little consequence, but I could be wrong). Assuming that the storm that formed ON the outflow boundary is able to REMAIN on the outflow boundary for a while, then it would be favored for tornadic production as opposed to a cell that is not associated with an outflow boundary.
An outflow boundary can locally enhance inflow with its stronger backed winds, and can result in locally lower cloud bases if one side of the boundary is relatively cool and moist. Outflow boundaries tend to be places where local low-level vorticity is enhanced, and tornados like that. So, you could have two similar non-tornadic supercells plugging away and working on similar air...and if one of them comes upon an old outflow boundary, with vorticity-rich air and higher relative humidities, then that one should be favored for tornado production.
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>Can they really make or break a big tornado event??
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I guess it depends on your definition of "big tornado event". As a chaser, you can only be on one storm at a time, so it doesn't matter if there are 100 tornadoes that day or just one ----- all that matters is what your storm does. But, yes, there likely have been many days with numerous tornadoes which would have been tornado-less had outflow boundaries been absent.
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> And finally, do supercells intentionally form on the outflow boundaries in >response to them or can they just by sheer coincidence bump into one of >them and then enhance tornado output/intensity?
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Both occur. Outflow boundaries can be excellent foci for convective development. On days with strong caps, it may only be along the old outflow boundaries where development is possible. And, once a supercell gets cranking after forming on the outflow boundary, it immediately becomes a prime tornado candidate as it is sitting on the boundary.
There are a bunch of ways to get supercells and outflow boundary interaction. Some "new" outflow boundaries might not be favorable at all if they are cool and rushing away from their parent storms and undercutting others. The Last Chance, CO, tornado that I saw in July 1993 was from a storm that formed on outflow from nearby storm that had been drifting along for hours. The initial storm formed on the dry line on the Colorado Plains and moved slowly east for several hours, and had problems making tornadoes. Its cool and moist outflow bumped into the nice moist southeasterlies to its southwest, and a new storm went up as sunset approached. The new storm rode the outflow boundary from the old storm and produced a couple of large tornadoes. The two storms were perhaps 20-30 miles apart.
The more typical way to get a "good" outflow boundary is from morning convection that spills out cool and moist air. Eventually this air stalls out as it comes up against the moist shoutherlies or southeasterlies to its south. Ideally, the boundary will remain in place through the afternoon, the low clouds associated with the cool air burn off, and the boundary bakes for a fews hours under the high sun. The convergence along the boundary might aid in storm development, and the backed winds (and the higher RH) on the cool side of the boundary would enhance low-level helicity values beneath the updraft.
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>Sorry for that barrage of rambling questions. I’m just really curious about >the play on tornadoes and outflows. Probably simple and common stuff to >you guys but it’s something I just never really looked into too >much.