Outflow Dominant?

[BBauer]

The media has been buzzing about this photo a bit taken of a supercell in MT. I have seen similar phenomena in other photos. The example I'm referring to is shown best in the second photo down. I'm basically seeing a very sculpted updraft but in the area where I would be looking for a tornado to form I'm seeing a big downdraft/rain curtain. I know storms get outflow dominated but more often than not it seems the outflow will be further away from the updraft. In this case it seems moisture is condensing and the rain is falling straight down through the pre-existing updraft. Does this occur when there is not enough upper level shear to tilt the updraft? I may be off base. Help me understand what I am seeing in this photo, thanks!

http://www.dailymail.co.uk/sciencet...enormous-supercell-cloud-Glasgow-Montana.html

 

[Skip Talbot]

Rain is falling straight down through the updraft (or where the updraft used to be) in that second photo. However, what you're seeing is the rear flanking downdraft. Often times what's being talked about when storms can't separate their updrafts and downdrafts is more referring to the forward flanking downdraft. You can see the forward flanking downdraft off to the right on that image, and you can see its well separated from that mothership shaped updraft tower. The rear flanking downdraft does punch through the updraft base and forms a a clear slot, which can preclude tornadogenesis. This is a favorable process that storm chasers look for rather than an unfavorable one when a storm transitions to outflow dominant. The fact that there is so much rain in this RFD means you're looking at a high precipitation supercell. This storm might be making the transition to an outflow dominant storm, but usually you see more scud, more turbulent bases, and a more bowed out rear flanking gust front. There is still a very well defined updraft base here. When a storm goes outflow dominant, these downdrafts take over and bury the updraft base in rain/outflow.

 

[BBauer]

Thanks, that clears things up a bit. Yes, I was wondering why there is a nicely sculpted updraft yet there is a big rain curtain falling straight down its throat. I guess I thought the RFD wraps around the outside of the updraft but its good to know it often (or always?) cuts through it.

 

[Rob H]

For reference, here's a side-on view of the same type of event, where it's cut right down the middle: