Weatherquest meteorologists Dan Holley and Chris Steele are once again set to fly out to the U.S. in search of one of the most powerful forces of nature... the tornado.
The storm season in the U.S. Plains occurs ever year generally from April through to June, as cold air from the North meets warm moist air from the Gulf of Mexico to the south. Several conditions are required for both the development of tornadoes and the thunderstorms that produce them. Abundant low level moisture is necessary, and a "trigger" is needed to lift the moist air aloft.
Norfolk storm chaser Steve Lansdell captures a tornado in Kansas during May 2013. Photograph copyright Pete Scott.
Once the air begins to rise and becomes saturated, it will continue rising to great heights and produce a thunderstorm (cumulonimbus) cloud if the atmosphere is unstable. An unstable atmosphere is one in which the temperature decreases rapidly with height. Atmospheric instability can also occur when dry air overlays moist air near the Earth's surface.
Tornadoes usually form in areas where winds at all levels of the atmosphere are not only strong, but also turn with height in a clockwise, or veering, direction. Most tornadoes in the United States occur east of the Rocky Mountains, across the Great Plains, Midwest, Mississippi Valley and southern United States.
You can follow Dan's and Chris' blogs here
We wish Dan and Chris the best of luck during their two-week hunt, between 14th - 27th May, and wish them a safe return.
Admin 11th May 2014
Sea Surface Temperatures: What a difference a year can make...
About this time last year, we wrote a news item about how cold the sea surface temperatures were at the beginning of March 2013 in the southern North Sea (especially near the East Anglian coast). What a difference a year can make; this year, it's hard to imagine such a turnaround. Temperatures on the 1st March 2014 were about 8.5C just off of the coast of Suffolk, compared to the same day last year when they were at 3.7C.
This marked change is the result of the two contrasting winter seasons that much of Britain has experienced. The winter of 2012-13 was dominated from January through March by a blocking area of high pressure over northwestern Europe which brought a persistent flow of very cold easterly winds, resulting in temperatures 1-2C below average for February 2013 and as much as 3-4C below average in March 2013. Winter 2013-14 has been quite the contrast with a very active jet-stream across the north-central Atlantic bringing successive storm systems from the west. This has brought wet and windy conditions to much of Britain, and as a result kept the southern North Sea from cooling down as much as it would on average.
Another interesting signal in the sea surface temperature difference from early March this year compared to 2013, is that the Atlantic to the west of the British Isles is generally colder than it was this time last year. This is also the result of the more unsettled and windy pattern to the weather across this part of the Atlantic during winter 2013-14. The windy conditions have lead to a more mixed top layer of the ocean water, which in turn has created slightly cooler sea surface temperatures compared to last year.
SST data source: NASA JPL
Chris Bell 10th March 2014
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