Bryan Bjorkman
I've read posts where people are talking about the double eagle on radar. What is that and what is the significance?
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David Drummond
Member
It's a nice looking supercell signature on radar that resembles an eagle in shape. I can't seem to find one to post. I am sure someone has one. The hook echo makes the beak and the precipe cores make out the wings. Kinda cool.
EDIT: Lon Curtis has one on his page about half way down:
http://www.vvm.com/~curtis/Radartechs.htmBryan Bjorkman
David
Since your online I am curious, in the video that you put together (excellent btw) after dark there was a funnel illuminated by lightning that you called in. Where exactly was that? I live in Lincoln and was south of the Hallam storm. I ended up running more than chasing after dark that night, lol. I flew over the entire track the next day and saw numerous other wind/tornado damage, just trying to get an idea of that funnels location. Thanks
David Drummond
Member
Going to PM you so as not to swing way off topic on this thread. :wink:Mike Hollingshead
[Broken External Image]:http://www.extremeinstability.com/stormpics/ainsworth7-24-00anim.gif
Man I love July in NE. Seems like about once a year(or more) there is a long-lived 'flying eagle' dropping south in the central part of NE.
Skip Talbot
EF5
Mike, would you say that's an HP sup judging off the broad range of high reflectivity? It certainly looks like it might be a little bit more work to chase because the core is bearing down on you if you setup on the southern flank. I guess you have to work this one from behind the hook.
David Drummond
Member
Just adjust your position based on storm movement. SSW would be decent here. Remember, storms don't know directions. Think like the storm, become one with it! :wink:Mike Hollingshead
Actually I've had the best luck EAST of the updraft base on those, or slightly south of due east. It was a classic.
http://www.extremeinstability.com/july_24,...a_tornadoes.htm
Both that one and the July 12, 2004 Bartlett storm were dropping ssw and I was pretty much straight east of the updraft base on both. If you are close enough to the updarft base and nearly under it precip blocking the view often isn't THAT big of an issue. The updraft is moving/forming south and the precip is being left a little "behind" it to the ne as it is vented to the east. So best viewing is still to the east. Others may say differently but from what I've seen.....
Edit:
http://www.extremeinstability.com/04-7-12.htm
East of updraft....
David Drummond
Member
Looking at your pics Mike, is it fair to say that the majority of the precip was fairly well separated from the updraft base, giving you a little more manuevering room in there?Mike Hollingshead
If it is a flying eagle it is fair to say it is fairly well vented yeah. There will still be precip....likely hail...close to that updraft base. But, like I said, often if you are east of that updraft base most of the precip is lagging a bit "behind" as it moves south-ssw. So most cases you are still going to be ok to the east to slightly south of just east. On the July 12 04 one there wasn't a great deal of venting(other than its storm motion helping out). It had about 20 knots at 500mb out of the west and 40 knots at 300mb out of the wnw and was very striking visually. Only 3-4 miles up the road to the north of me and you were in a whole nother world of heavy rain...but that was getting more ne of the updraft base.
Greg Stumpf
EF5
I'm surprised that nobody has replied to offer the explanation for the shape of the echo, particularly the V-notch in the forward flank. Some feel that this is the result of "flow around the obstacle", with the obstacle being the updraft, with the notch being the wake. Comments?Glen Romine
EF5
Are you one of the 'some'? Just curious. I agree that this is a tempting explanation - as the updraft carries the momentum of surface air aloft - and theoretical and model calculations have indeed shown the stagnation high that develops aloft on the upshear side of the updraft. But, a strong updraft is a signature feature of supercells, and not all supercells show the flying eagle / v-notch signature, though some cells seem to show it at various times and not others. You could perhaps argue that the updraft often sits along the right flank edge, but moves closer to centerline as the mesocyclone intensifies and then is more apt to block the flow through the main precip core, but I've never seen this transition clearly demonstrated in a study. There might also be reason to suspect differences in microphysical processes as being a player, as polarimetric radar data suggests. I've never seen a satisfying explanation of the cause beyond the blockage one - but I'd be interested if anyone knows of a definitive description of this phenomena.
Glen
Robert Dewey
EF5
I personally like the updraft theory. It would make sense that mesoscale divergence aloft would be generated because upper level winds are being forced around an object. While upper level divergence usually leads to ascent, I believe in this case that the "forced" divergence may actually lead to descent. This is because the airstream would try to rush back in behind the storm, and actually converge, causing descent, much like the rear inflow jet, and the associated Weak Echo Channel. I have illustrated this quickly to show what I mean:
http://69.14.190.10/images/storm_theory/st..._divergence.jpg
And then applied to an actual storm:
http://69.14.190.10/images/storm_theory/52896_pic5.gif
The way I like to look at it is like a rock in a stream of water. The water moves around the rock, diverging... But, on the other site of the rock, the water actually flow TOWARDS the rock, and with a downward motion...
I hope I am making sense :lol:
Greg Stumpf
EF5
One of the concerns about the obstacle theory is that the updraft is not a solid body, like a rock in the stream. The updraft is also fluid.Glen Romine
EF5
Also, you need to be careful about the layout of the blockage (updraft) relative to the storm features. In your diagrams, the split is not where the updraft is located. Here is perhaps a better representation:
[Broken External Image]:http://www.atmos.uiuc.edu/~romine/img/notch_model.jpg
The peach color is the main precip core (say > 40dbz), the purple is the storm updraft, green arrow aligned through the main updraft aligned with the mid-level flow, blue lines maring the wake region downshear from the updraft, the 'H' and 'L' the relative mid-level pressure fields owing to the blockage by the updraft, and the black lines might represent the perturbation flow around the blockage. The yellow flow pattern sort of seems to make sense to me, as in the acceleration of flow around the north side of the updraft elongating the reflectivity field as shown. However, the lobe on the south side of the echo doesn't seem as intuitive in this perturbed flow model - as you'd expect the southern edge to be heavily rounded as the echo 'emerges' out from behind the flow obstruction - but instead it seems to not really fit.
As most folks that have hung out in cores much can tell you, the hail is located immediately north to northeast of the updraft for a layout as shown in the image above, and smaller hail often extends down the 'wing' (southern half of 'V') of the eagle shaped echo, with typically just heavy rain in the 'body' (northern half of 'V') portion of the echo. The reason for the void in between might be in part due to the perturbed flow due to the updraft, but the southward extension of the echo probably has more to do with extreme storm-top divergence fanning out the precipitation at the top of the updraft.
GlenSimilar threads
