General newbie questions (to be continued)

[Skip Talbot]

* Regarding downbursts. As far as I understand downbursts are not a continuous part of a storm but rather something that happens when a part of the storm collapse and bring a huge chunk of air to the ground? Or, could a downburst go on for a long time in a storm?

Generally anywhere experiencing rain, hail, or precipitation is also experiencing a downdraft. Precip is ongoing throughout the life of the storm, so the downdraft is too. Like James explained, however, there are more intense spurts within this ongoing downdraft that get labeled as downbursts.

To me this term has less significance to storm chasers than it does to residents, damage survey crews, and pilots. These folks witness specific swaths of intense winds or damage and thus label them as specific events, over well defined areas. A chaser generally witnesses just large areas of wind and rain, however, and picking out the spots within that have locally stronger gusts is difficult to do visually.

Where is the downdraft in this picture? It's the green area where it's raining. Do I look at this and call it a downburst?

No, I'd call that (in this case) the forward flanking precipitation core or forward flanking downdraft, and inside of it I'd expect there to be some severe winds. An area inside of this storm did produce a damaging downburst over a relatively narrow swath. Since I can't really see it as it's just more rain and wind inside of a large area of rain and wind, I just refer to the whole area as the downdraft. To the damage survey team and residents in the path, this was a specific event since a well defined swath of damage occurred.

You'll certainly see more textbook examples while chasing:

The waves visible at the bottom left edge of this FFD on the May 23, 2008 Quinter, KS supercell would be associated with severe straight line winds and labeled a downburst. This happens frequently on storm gust fronts and within the core, however, and is often not as visible since that structure is often obscured by more rain. There are likely the same waves heading towards me in the area to the right, but I can't see them because of the precipitation core behind them.

So your original question: yes, it's possible to have a long duration, ongoing downburst. Usually it's a short lived spurt of an ongoing downdraft though.

 

[ChristofferB]

Post-Storm Analysis: this SPC page enables you to see tornado, high wind and large hail reports on a map. Once you have a map up for the desired period, you can also click on a Google Maps link that overlays the reports in the exact area and you can zoom in to a very detailed level: http://www.spc.noaa.gov/climo/online/

That's exactly what I was looking for, I should have guessed SPC would have had that as well!

Thanks also to you and Skip (again) for your great answers regarding downbursts! I think I have a good hang out of the most basic things regarding storm cloud analysis now.

 

[Paul Knightley]

Great image on the last page, Skip (the El Reno radar with annotations). One thing I might add is that I believe that some recent findings have suggested that, at ground level at least, tornadoes may not be drawing air from the 'warm' inflow, and all air entering the tornado at base level has already been 'processed' by the storm, to a greater or lesser degree. I'd be interested in knowing whether anyone has come across more detailed info about this hypothesis.

 

[Skip Talbot]

t ground level at least, tornadoes may not be drawing air from the 'warm' inflow, and all air entering the tornado at base level has already been 'processed' by the storm, to a greater or lesser degree.

This is a great point, and most of the supercell schematics indeed show the tornado forming on the occluded part of the RFD/FFD/inflow front where the warm moist inflow has already been pinched off. I'd be curious to see the trajectories of the storm's inflow at the time of the tornado. The tornado's inflow is definitely coming from behind it, right off the RFD it seems. I've also experienced very strong SE or E inflow while east of the RFD gust front (clear air ahead of the storm) at the time of tornadoes too though. The direction of the inflow seems to track with the tornado as it moves, and if I can't see the tornado, I generally guess where it is or might be just based off of the inflow direction. Of course that doesn't mean this inflow is funneling directly into the tornado. It's probably getting forced up and over the RFD at some point and into the tornado cyclone or the mesocyclone.