Last night(November 5, 2017), at 1:48 AM CDT, a squall line moved through western TN. There was strong wind and heavy rain, but no lightning and thunder. Is there such a thing? I’m thinking of two possibilities: 1. The squall line was all nimbostratus. (Not likely at all) 2. Cb clouds produced no lightning or thunder. (Not likely either) Can someone explain what happened? I searched through the internet but couldn’t find anything.
Probably 2. There are others here who know a lot more about lightning than I do, but the likely explanation is that, although you did have CB, there was not enough temperature contrast to get lightning. Warm cloud bases combined with frozen cloud tops, usually with graupel present in the clouds, are the type of condition where you get lightning. In this case, although the storm process was convective, I would guess that the cloud bases were not particularly warm (it was night in November, after all) while the cloud height may have been somewhat shallow resulting in less cold cloud tops. So not enough temperature contrast from bottom to top of the clouds to get much in the way of lightning, even though the clouds were convective.
To add to John's points, low-topped convection can produce all types of severe weather without lightning. It is usually during low-CAPE, high shear days during the cool season (fall through early spring). It is also common for "cold core" tornado days to have little or no lightning.
First, you need ice phase hydrometeors to get lightning. If cloud tops were short enough so that there was no ice in the cloud, you will not get lightning. Second, even if you do get ice phase particles, they need to interact to build up charge separation. If instability and subsequent updrafts are very weak, there may not be enough motion within the cloud to get sufficient levels of charge separation and thus insufficient potential for lightning. Third, it's possible there was lightning but you didn't see it nor hear the thunder either because -it was too distant -the thunder was covered by other sounds If you have quantitative evidence in the form of NLDN or GLM data proving otherwise, then I would bet there actually was some amount of lightning, but you just didn't notice it.
We quite often get squall lines in the UK with little or no lightning. As well as what has been mentioned above, sometimes very shallow convection occurs at the leading edge of a 'surge' of cool/cold air - such 'forced' convection (which is really just almost stable air being rapidly lifted in the lowest 1-2kms of the atmosphere) can lead to very heavy rain and strong winds, but no lightning. E.g. http://www4.ncsu.edu/~nwsfo/storage/training/jets/narrow.html
Thanks to all that have replied. Another question: is it possible to have a squall line composed of only nimbostratus? A more advanced question: what happens when a supercell gets surrounded by a squall line? Example: a multiple tornado-producing supercell is going NE at 10kts, but a squall line comes up about 2km behind it and travels at 40kts. That squall line engulfs the lone supercell.
1) No, as stratus implies non-convective activity. 2) Depends, but usually the supercell is absorbed by the line and the tornado threat ends.
As rdale said, it seems like most of the time the supercell will become absorbed by the line or weaken/diminish prior to the line intercepting it. However, there are some cases where the interaction between the squall line and supercell will produce a tornado or bow echo/wind damage. One of the more well-known cases is the Hunstville, AL tornado on November 15, 1989. Also, if anyone wants to do some reading, squall line and supercell mergers have been formally researched here: http://journals.ametsoc.org/doi/abs/10.1175/WAF-D-11-00058.1
I’m not sure, but I’ve read somewhere that one time, a bow echo hit a supercell(classic), the bow echo rapidly weakened, and the supercell moved from classic to high-precipitation, while producing more tornadoes.
That doesn't seem likely - as noted in the article above the rotation is going to be disrupted if the bow echo has any structure to it.
The situation you described actually occurred in eastern Oklahoma during the evening of April 17, 1995: http://journals.ametsoc.org/doi/abs/10.1175/1520-0434(1998)013<0492:WRDOSB>2.0.CO;2 I would say that situation is pretty rare. Typically the squall line/bow echo is going to win out. If tornadoes occur after the merger and after the supercell diminishes, they're going to be tied to shallow mesovortices associated with the leading edge of the line. These are common in squall lines and occur regardless of a merger.
In the article, after the hp supercell merged with the bow echo, the rotating mesocyclone evolved to become more of a widespread rotation concentrated in the top-middle of the new supercell. Why/how did the mesocyclone evolve to become a larger mesoscale convection?
Such a term does not exist. Are you perhaps thinking of "mesoscale convective system" or "mesoscale convective vortex"? Try perusing the AMS glossary (http://glossary.ametsoc.org/wiki/Main_Page) to check some definitions.
I don't think he was being toxic? Or is correcting an error toxic now? From reading the article, I assume you meant large mesoscale "circulation". What I'm getting from the article is that rather than the bow echo overtaking the supercell, the two merged and ultimately created something like a miniature MCV with embedded mesocyclones producing tornadoes within the larger circulation.
Ok. Thanks! Last thing(s). I promise! Where do tornadoes occur in bow echoes, and why didn’t the supercell just become embedded(not combined with the bow echo)?
Usually tornadoes in bow echoes are associated with mesovortices that develop along the leading edge of the bow echo, usually from the apex of the bow echo northward. Sometimes these mesovortices form where the bow echo interacts with some kind of pre-existing boundary from another storm, such as an outflow boundary. Tornadoes can also occur with circulations that form at the northern end of the bow echo; these are sometimes referred to as bow-head tornadoes. And as discussed above, tornadoes can occur if a supercell that initially formed ahead of the line is absorbed into a bow echo or squall line. I am not exactly sure what you mean by the difference between becoming embedded in and combined with the bow echo; to me these terms refer to a similar process.
