NON Mesocyclonic Tornadoes

[Kevin Norton]

Hey All,

Does anyone have any basic theory or flow description on NON meseocyclonic tornadoes?

Mesocyclonic generated tornadoes sort of "make sense " to me, despite not having a really in depth grip on theory.

But despite isolated recent exceptions ( ie Springfield, MA), NON mesocyclonic tornadoes seem much more the norm here in New England ( 2 or 3 per yr in MA ?). I would like to learn more about the mechanisms involved in these storms.

I live in Boston . The small,short lived EF0 or EF1 non mescyclonic "rope" tornadoes that are "typical" of New England "almost never" form this far East or Southeast.

We have our own "mini Tornado Alley" including W and Central CT, W and Central MA,maybe SE VT and maybe extreme NE MA.

Thanks, Kevin Norton

 

[Jeff Snyder]

There are two primary "types" of non-mesocyclone-produced tornadoes:

1. "Landspouts" -- these have a relatively consistent appearance, often with a mostly-transparent, nearly constant-width tube between a small funnel that typically doesn't extend from cloud base very far. I'm sure you've seen pictures of these; if not, you can probably find a bunch via a Google search. These are comparatively common in the high Plains (eastern Colorado, etc.), and they are typically caused by vertical stretching (sometimes only in just a cumulus or towering cumulus cloud) of pre-existing vertical vorticity often maximized in misocyclones ("i" instead of "e").

2. QLCS tornadoes -- there are times when supercells are embedded within squall lines, but there are also many times when relatively shallow vorticies can exist along the leading edge of a quasi-linear convective system. Dealing with these typically short-lived circulations has been a source of controversy as we've seen some NWSFOs issue very large tornado warnings (spanning 5-8 counties along a segment of the QLCS) to cover this threat. You'll often see these associated with small protrusions of precipitation that extend outward from the leading edge of the QLCS, and are more common in the eastern U.S..

Of course, there can also be "mesoscale accidents", of sorts, wherein various surface boundaries collide and create a typically short-lived environment that supports tornadoes. Typically these events tend to enhance potential for a tornado from a nearby supercell, but I don't see why they also wouldn't be possible with strong multicells.

 

[Kevin Norton]

Thanks Jeff,Very interesting info.

Kevin Norton ,N1NQC

 

[Jeff Wright]

Some discussion on warnings for weaker tornadoes

http://www.alabamawx.com/?p=48699 http://www.alabamawx.com/?p=48880

 

[Greg Stumpf]

1. "Landspouts" -- these have a relatively consistent appearance, often with a mostly-transparent, nearly constant-width tube between a small funnel that typically doesn't extend from cloud base very far.

Be cautious of this characterization of landspouts. This might be a good visual description of a landspout in a dry high-cloud base environment like the High Plains, but many of the tornadoes that occur along the Florida coasts in the summer are also landspouts. These occur along sea-breeze convergence zones and are frequently characterized by lower cloud bases and condensation funnels to the ground, owing to the higher humidity there. But you can even get (relatively) high-humidity landspouts in the High Plains. The second landspout I ever observed in Colorado (near LaSalle) had a condensation funnel in contact with the ground.

 

[J Allen]

Well made point Greg. I also believe the paper Monterverdi et al. from SLS 2010 talking about the eastern moving storm in Kiowa County CO on the 25th of May 2010 was also a good example of where to be careful with landspouts. IIRC that storm was producing condensed non-mesocyclonic tornadoes and mesocyclonic tornadoes simultaneously, and produced a flurry of non-supercellular tornadoes prior to the storm becoming the cyclic tornado producer.

 

[Bobby Prentice]

I started a Non-Supercell Tornadoes (Waterspounts/Landspouts) topic subject in the Advanced Weather and Chasing forum back on October 31, 2006. Here is a copy of my original post:


A landspout is a form of non-supercell tornado occurring with a parent cloud in its growth stage (e.g., towering cumulus) and with its vorticity originating in the atmospheric boundary layer. Waterspouts are another form of non-supercell tornado and basically form the same way.

ORGANIZING STAGE

Landspouts/waterspouts form along convergent, horizontal wind shear boundaries where cumuliform clouds are rapidly growing. Small atmospheric boundary layer vortices called misocyclones form and propagate along these boundaries (particuarly near boundary intersections).

The "[FONT=Verdana, Arial, Helvetica, sans-serif]0-3km CAPE (J/kg) and Sfc Vorticity" graphic from the SPC Hourly Mesoanalysis [/FONT]web page provides perhaps the best weather chart to see this enviroment in real time. This page is generally best because it includes national mesonet surface data (from MesoWest) and RUC model data in its analysis.

MATURE STAGE

A landspout/waterspout may form when a convective updraft becomes co-located with one of these misocyclones. The landspout/waterspout circulation developes from the ground upward as the pre-existing vertical vorticity is streched by the updraft. The horizontal diameter of the misocyclones decreases which increases the rotational velocity of ciruclation. This is process is analogous to a figure skater which spins faster and faster as she brings her arms in closer to her body. The strongest rotation remains below the cloud base in the atmospheric boundary layer.

WSR-88D radar loops and 1 km rapid-scan visible satellite loops are necessary for further interrogation and detecting fine scale details in growth and development.

DISSIPATION STAGE

Precipitation induces a downdraft within the vortex. The landspout/waterspout weakens and its vertical exent is reduced as the cumuliform cloud's updraft weakens.

One of the biggest problems warning forecasters experience is the landspout/waterspout has often dissipated when a precipitation echo has reached the surface. However, is one landspout/waterspout has developed the mesoscale environment is often primed for more to form.

FORMATION CLUES

Favorable radar indicators for non-supercell (landspout/waterspout) tornado development include:

- Boundaries exhibiting strong horizontal wind shear
- Collision points of two or more boundaries (example)
- Boundaries possissing wave-like inflections (scalloped appearance) suggesting circulations
- Rapidly developing storms near low-level circulations
- Region along a boundary possessing high radar dBz reflectivity values in clear air return (signature of strong convergence)
- Boundaries with high radar specturm width values (which imply strong wind shear)

RADAR DETECTION PROBLEMS

- Landspouts/waterspouts may form before any precipitation echo has developed.
- The small horizontal extent of the circulation limits the detectable range.
- The strongest rotation is confined to low levels (the atmospheric boundary layer).

Thus, radar horizon problems prevent us from seeing boundaries beyond about 50-60 miles from the radar and misocyclones beyond about 20-30 miles.

 

[Kevin Norton]

I appreciate this interesting info.

KLN N1NQC