Storms

[Cloudburst]

Remember that fantastic night-time display that occured last year?

It was set-off as a cell moved northwards from France and was very impressive.

It gave Bristol a brilliant electrical show and reports of damaging hailstones.

Further north, very heavy rain formed as the cells exploded in size very rapidly.

The CAPE, I remember, was much lower than would usually be expected for such a storm (around 800 or so).

Yep May 1st Stayed up from 1:30am till 4:30am, and by the time i decided to go to bed it was still lighting the sky up. High level storms, the thunder is faint and has an odd sound to it, lightning was almost constant. :huh:

[Nick F]

Yep May 1st Stayed up from 1:30am till 4:30am, and by the time i decided to go to bed it was still lighting the sky up. High level storms, the thunder is faint and has an odd sound to it, lightning was almost constant. :huh:

Quite a good account of those mid-level severe storms on May 1st last year Here

[Roger J Smith]

I don't know if perhaps I am totally misunderstanding comments made above, but there is no possible way that the UK experiences more tornadoes than the USA on any comparative scale, whether it would be events per square km, events seen by people, or events in total. In fact, I would estimate the relative chance of a point in the central U.S. seeing a tornado in a given period as 100 to 1,000 times greater than the chance of a point in the UK seeing one. There might be more of a 1:1 ratio if you took areas outside the main tornado zone such as the New England states. I'm sure nobody would advance an argument comparing intensity, but this argument regarding frequency has been advanced here before and also on other UK weather sites, and frankly I find it entirely inconceivable.

The U.K. is roughly the same size as Kansas or Missouri so you could easily check out the statistics and verify that the frequency is far greater in the central United States. A state like Kansas or Missouri can expect to have several hundred tornado reports in the average year. Even in Ohio or Michigan which are not in the main part of "tornado alley" there are probably ten times as many tornadoes per year as in southern England. The part of the argument that does resonate with me is that tornadoes are more frequent than some people imagine in more temperate climate zones. They also occur largely unreported in the wide open spaces of the Canadian prairies and in sparsely populated northern Ontario. I remember coming across an obvious tornado damage trail with rotation of fallen trees about a mile from a summer camp where a heavy thunderstorm without wind damage had been experienced the previous night. Nobody in the camp had any idea that a tornado, probably an F2 from the size of trees down, had come that close to where 200 people were gathered.

[Cloudburst]

I don't know if perhaps I am totally misunderstanding comments made above, but there is no possible way that the UK experiences more tornadoes than the USA on any comparative scale, whether it would be events per square km, events seen by people, or events in total. In fact, I would estimate the relative chance of a point in the central U.S. seeing a tornado in a given period as 100 to 1,000 times greater than the chance of a point in the UK seeing one. There might be more of a 1:1 ratio if you took areas outside the main tornado zone such as the New England states. I'm sure nobody would advance an argument comparing intensity, but this argument regarding frequency has been advanced here before and also on other UK weather sites, and frankly I find it entirely inconceivable.

.

Per Square Kilometer the u.k on average has the same frequency as the plains.

[Supercell]

The high frequency is down to most of the rotating columns occuring as waterspouts in the waters around the UK. Tornadoes overland are a lot less common.

[Thundersquall]

The high frequency is down to most of the rotating columns occuring as waterspouts in the waters around the UK. Tornadoes overland are a lot less common.

I'm not surprised the UK experiences the same level of tornadoes as the USA plains.

Even in today's brisk wind an eddy was causing paper to whirl around by a sheltered outside wall at Bath Abbey.

Edited April 2, 2006 by Thundersquall

[kold weather]

The main difference to the UK is that most tornadoes here are what some people call cold cored tornadoes, the type that are formed without a mesocyclone present, these tend to be weak though. The USA tend to get the other version that involves a deep mesocyclone in a supercell.

[BrickFielder]

I don't know if perhaps I am totally misunderstanding comments made above, but there is no possible way that the UK experiences more tornadoes than the USA on any comparative scale, whether it would be events per square km, events seen by people, or events in total. In fact, I would estimate the relative chance of a point in the central U.S. seeing a tornado in a given period as 100 to 1,000 times greater than the chance of a point in the UK seeing one. There might be more of a 1:1 ratio if you took areas outside the main tornado zone such as the New England states. I'm sure nobody would advance an argument comparing intensity, but this argument regarding frequency has been advanced here before and also on other UK weather sites, and frankly I find it entirely inconceivable.

The U.K. is roughly the same size as Kansas or Missouri so you could easily check out the statistics and verify that the frequency is far greater in the central United States. A state like Kansas or Missouri can expect to have several hundred tornado reports in the average year. Even in Ohio or Michigan which are not in the main part of "tornado alley" there are probably ten times as many tornadoes per year as in southern England. The part of the argument that does resonate with me is that tornadoes are more frequent than some people imagine in more temperate climate zones. They also occur largely unreported in the wide open spaces of the Canadian prairies and in sparsely populated northern Ontario. I remember coming across an obvious tornado damage trail with rotation of fallen trees about a mile from a summer camp where a heavy thunderstorm without wind damage had been experienced the previous night. Nobody in the camp had any idea that a tornado, probably an F2 from the size of trees down, had come that close to where 200 people were gathered.

The origin of the comment is from Dr. T. Fujita of the Fujita scale and when you total up all the tornadoes reported in the US over a year and divide by the total area of the US you get the probability of a tornado per square mile. This is less than for the UK. The reasons for this are similar to why california had a very active tornado season last year and why Florida reports more tornadoes per square mile than Texas. The UK does not see the same intensity of tornadoes as a state like Texas or even the number of tornadoes, with something like 30/50 reported each year in the UK so if you compare the plain states only then these have more tornadoes.

The average number of tornadoes for 1989-1998

Texas (168), Oklahoma (55), Kansas (75), Florida (79), Nebraska (57)

Taking into account the sizes of these states this works out to

Texas 6

Oklahoma 8

Kansas 9

Florida 12

Nebraska 7.5

per 10000 square miles.

Over the same period (89-98) the reported number of tornadoes per year in the UK in England(as opposed to UK) is around 30 per year which equates to around 6 tornadoes per 10000 square miles. If you look at each area of England then the midlands and east anglia record about 20 tornadoes per 10000 square miles much higher than any county or state in the US but not as high as parts of Holland, South Africa and Australia.

SPC Tornado Averages per Year US

MetOffice Tornado Figures

Edited April 11, 2006 by BrickFielder

[NL]

All this begs the question how is CAPE determined?

SKEW-T: A LOOK AT CAPE

METEOROLOGIST JEFF HABY

1. What is CAPE?

CAPE (Convective Available Potential Energy) is the integration of the positive area on a Skew-T sounding. The positive area is that region where the theoretical parcel temperature is warmer than the actual temperature at each pressure level in the troposphere. The theoretical parcel temperature is the lapse rate(s) a parcel would take if raised from the lower PBL.

2. How is CAPE determined?

The positive area on a sounding is proportional to the amount of CAPE. The higher the positive area, the higher the CAPE. The positive area is that area where the parcel sounding is to the right (warmer) than the environmental sounding. The units of CAPE are Joules per kilogram (energy per unit mass). The sounding at the bottom of this page shows a CAPE value of 2,032 Joules per kilogram.

3. Operational significance of CAPE:

CAPE

1 - 1,500 Positive

1,500 - 2,500 Large

2,500+ Extreme

High CAPE means storms will build vertically very quickly. The updraft speed depends on the CAPE environment.

Hail: As CAPE increases (especially above 2,500 J/kg) the hail potential increases. Large hail requires very large CAPE values.

Downdraft: An intense updraft often produces an intense downdraft since an intense updraft will condense out a large amount of moisture. Expect isolated regions of very heavy rain when storms form in a large or extreme CAPE environment.

Lightning: Large and extreme CAPE will produce storms with abundant lightning.

4. Pitfalls:

a. Storms will only form and the CAPE actualized if the low level capping inversion is broken.

b. CAPE magnitude can rise or fall very rapidly across time and space.

[Guest Mr_S]

http://www.netweather.tv/forum/index.php?showtopic=16002