outflow boundary

[Lanny Dean]

Yes. I would have to say 80% of my tornadoes have been in direct relation to outflow bundries. Take the pig farm tornado in Oklahom back in 2008. That cell i was on rode an outflow boundry all day, and produced numerous tornadoes. I would however have to say that iv noticed some cells have not produced once intersecting outflow boundries due to perhaps the orientation of the boundry. Dont get me wrong, iv seen a supercell literally completly change its path once it intersected the boundry, 110 degrees to follow the outflow boundry and produce numerous tornadoes. On the other hand, iv seen a NESW oriented boundry intersect a NE moving cell, and have nothing happen. No increased SREH, and minmal surface backing was increased. Iv seen more cells go tor when there riding the SOUTH side of the boundry then the NORTH side of it. Its interesting how these mesoscale fetures all interact with eachother.

hmmmm.... interesting!

 

[Steve Miller TX]

Here are some good satellite images of outflow boundaries in action:

http://cimss.ssec.wisc.edu/goes/blog/archives/2812

http://www.umanitoba.ca/environment/envirogeog/weather/lasatpix.html

Adding to the good discussions in this thread, my preferred outflow boundary (OFB) is one created from overnight or early morning convection. This gives the generated cold pool enough time to "spread out" with the OFB becoming stationary or slowing to a crawl as afternoon heating ensues. Fast moving OFBs tend to quickly undercut storms as well as a storm being unable to remain rooted along it to take advantage of the horizontal vorticity the boundary provides. I also like to see an OFB intersect a stationary or very slow moving cool front or dryline too. Even better if the boundary ends up oriented roughly parallell to expected storm motions.

My $0.02

 

[Eric Duncan]

Here are some good satellite images of outflow boundaries in action:

http://cimss.ssec.wisc.edu/goes/blog/archives/2812

http://www.umanitoba.ca/environment/envirogeog/weather/lasatpix.html

Adding to the good discussions in this thread, my preferred outflow boundary (OFB) is one created from overnight or early morning convection. This gives the generated cold pool enough time to "spread out" with the OFB becoming stationary or slowing to a crawl as afternoon heating ensues. Fast moving OFBs tend to quickly undercut storms as well as a storm being unable to remain rooted along it to take advantage of the horizontal vorticity the boundary provides. I also like to see an OFB intersect a stationary or very slow moving cool front or dryline too. Even better if the boundary ends up oriented roughly parallell to expected storm motions.

My $0.02

Yeah no doubt Steve. I saw this "undercutting" action in place back in early June when i was in SE Kansas, and went bust like almost everybody else. The (OFB) was moving fairly quickly, about 35-40 mph, and intersected the cell i was on. The cell was tornado warned for a short period of time once it encountered the OFB, had some small low level rotation, but then quickly became outflow dominate and screamed NE. The OFB was moving nearly due south if i recall, and the storm was moving NE, which would correlate directly with what your saying in regards to the cell more likely becoming rooted ina OFB that is parallel with the storm motion, unlike this instance.

 

[Eric Duncan]

Excellent point Brian. I have seen many days when the airmass never modified behind the boundary and new convection developing along the boundary quickly became undercut. In fact June 9th in southern Kansas is an excellent example.

Yeah Greg that was crazy. As i was just saying earlier about how everything got undercut that day, there was a very sharp contrast in temperatures that day behind this boundry, along with the cloud cover. Too bad that had to happen, could have been a big day.

 

[Connor McCrorey]

I think the problem on 6/9 wasn't as much the OFB, as it seemed to stall in S KS while the convection was mainly in OK. However, the low level winds SUCKED, staying nearly SWerly all day.