Tornadoes Close To Record Low Level
By Paul Homewood
Provisional tornado numbers up to the 30th July are one of the lowest on record, according to NOAA’s Storm Prediction Centre.
The figures are based on LSR’s, or Local Storm Reports. It usually takes about three months for tornadoes to be confirmed and graded, with some LSR’s discarded as either duplications or found not to be tornadoes.
The top chart uses percentiles, based on 1954-2012, so giving a longer historical perspective. As many smaller tornadoes were not even reported in earlier decades, the SPC adjust earlier years up to compensate.
Last year’s tornado numbers were also extremely low, which is interesting given the contrast in US temperatures between last year and this. The two GISS maps below show the Spring temperature anomalies for each year.
The SPC themselves admit they don’t understand how tornadoes form, but an important ingredient is the collision of cold, dry air and warm moist air. In 2012, most of the country, and certainly tornado alley, was consistently warm. This year, it has been consistently cold, even down to the gulf. By and large, the conditions needed for the collision of warm and cold air have not existed.
Now contrast the last two years with 2011, when tornadoes were near to record highs. The difference is very obvious.
Most tornadoes occur between April and July, so, fingers crossed, tornado numbers will remain at a very low level for the rest of the year.
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