What cell feature is this?

[Tim Moxon]

We were on a cell in Colorado on June 12 and saw the feature below.

We are only a week into our first chase-cation, and still pretty newbie in terms of understanding what we see. It appears to be a condensation inflow (or maybe outflow?!). Could anyone advise on what this feature is?



Many thanks,

Tim

 

[Jody Radzik]

My guess, much less educated than that of others around here, is that it's an inflow feature vectoring off outflow running along the ground.

 

[Dave Kaplow]

I'd have to say outflow, or at least I would call it an outflow feature. I've seen these fingers of scud before, features virtually identical to the posted picture, usually with big HP hailers but always with an outflow dominant storm. They do sometimes look like tornadoes and occasionally they get called in as such by overeager sheriffs, but they don't rotate, they're just scud being pushed around by outflow.

 

[cdcollura]

Good day all,

It looks like the "side" view of a shelf cloud / gust front.

 

[Rob H]

Hi Tim,

We were probably very close to that same position on that cell. It seemed to be rain cooled rair getting ingested back into the storm with some gust front-type characteristics. The "top" part was a wall cloud but looks very ragged and minimal in your picture. There was definite lift in the scud, but it also had anticyclonic rotation in there which is not what you want to see in a wall cloud feature (outflow clashing with inflow). The inflow at this time was very cold, the wall cloud was very ragged and unorganized, VIL/reflectivity/velocity were all rather weak at the time - the storm looked like it was going outflow dominant and was about to die out. It eventually reorganized a little (you can see this in my picture from the 6/11 Reports thread) but we were very close to bailing on this cell when we saw the storm as it was in your picture. We didn't see anything else compelling to move to, and this cell had already been around for several hours with a history of cycling and reorganizing so we rode it out until the end.

edit: The more I read Jody's description, the more I like it. One simple sentence easily conveyed what my entire paragraph was trying to sum up

 

[Tim Moxon]

Thanks all - that's some great info - reckon you've nailed it, and I can read some more up on it having been pointed in the right direction.

Robert - glad there were others around to enjoy it...only saw one or two other chasers for miles, while not the most amazing cell I'm sure, it was nice to have one so rural we could get around without fighting past the whole of V2 etc!

Cheers again all,

Tim

 

[Gene Moore]

I won't get into the wind flow dynamics, that's already been covered.

Storms that leave hail (on the ground) in their wake often have this scud on the ground type features. This can be extrapolated to other parts of the storm. If the FFD hail path of a (hard) right turning supercell intersects the inflow then tail cloud on the ground results. That is, it effectively lowers the LCL by hundreds to a couple thousand feet given the same vertical lift.

 

[Skip Talbot]

Good points by all. This is definitely inflow structure similar to that of a wall cloud where its ingesting rain cool aired. I have seen this structure several times:

June 5, 2009:

If you got timelapse video of the feature I believe you might see some rotation. There was definitely rotation in the feature above, but it was very, very weak. I believe this may also be a failed tornado attempt. Although the feature condensed most of the way down to the ground, it couldn't wrap itself up enough to get a tornadic level of rotation. Had the processes involved that created this been stronger, you may be looking at a legit tornado. I'd label it inflow scud.

 

[Jason Harris]

Storms that leave hail (on the ground) in their wake often have this scud on the ground type features. This can be extrapolated to other parts of the storm. If the FFD hail path of a (hard) right turning supercell intersects the inflow then tail cloud on the ground results. That is, it effectively lowers the LCL by hundreds to a couple thousand feet given the same vertical lift.

Could you elaborate with more examples and details. Height and position of wall cloud relative to LCL level with pic examples would be ideal, or maybe another thread covers some of that? How LCL varies during life of storm is something it would be great to hear more about and how that relates to structure and tornadoes. I only know the general idea lower LCL better in relation to LFC:

From personal observations of the authors and of RB98, supercells above deeply mixed convective boundary layers, with relatively large dew point depressions and high LCL, often do not produce tornadoes even in environments of large CAPE and/or vertical shear which otherwise are considered “favorable” by operational forecasters. Hypothetically, stronger evaporational cooling of moist downdrafts leads to greater outflow dominance of storms in high LCL settings (RB98). We found LCL to be markedly lower for supercells producing significant tornadoes than for those producing weak tornadoes, which were in turn lower than for nontornadic supercells (Fig. 1). In fact, LCL for supercells producing strong and violent tornadoes was roughly half that of nontornadic supercells. In our analyzed data set, no strong and violent tornadoes occurred with LCL >1500 m

that's from 2000--maybe more news since then conclusion-wise?
http://www.spc.noaa.gov/publications/edwards/part2.htm

 

[Paul Knightley]

Yes, as others have said this is outflow - it actually looks like the 'top' portion of the low cloud/scud is marking the edge of the density current (outflow) as it moves out of the storm.