Storm Chase 2016



Weatherquest meteorologists Dan Holley and Adam Dury are 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.

A supercell thunderstorm becomes outflow-dominant above Kanorado (KS) in June 2015. Photograph by Dan Holley

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.

Norfolk storm chaser Steve Lansdell captures a tornado in Kansas during May 2013. Photograph by Peter Scott

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.

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We wish Dan and Adam the best of luck during their two-week hunt, between 18th - 31st May, and hope they have a safe return.

Admin  13th May 2016


Has this winter been exceptionally windy?

Has this winter (so far) been exceptionally windy? That's been one particularly popular question over recent weeks. Data from NCEP suggests that for the months of November-December-January combined, mean surface winds have been much stronger than normal, especially across southern Britain and the Southwest Approaches - this is, of course, relative to average and does not necessarily suggest that southern Britain has been any windier than elsewhere in the country - Scotland, for example, is more accustomed to stronger winds than areas farther south, so even if it had been equally windy in Scotland and southern England this winter, there would still be a larger anomaly showing farther south where it is often not as windy.

The graphic below compares the same period with the previous 2 years, and while not strictly speaking 'winter' (which meteorologically is defined as December-January-February) it does indicate that so far this winter it has been much windier in parts of the country compared to the past 2 winters.

Another interesting aspect is that the mean wind direction (the arrows on the maps) highlight that the source of air so far this season has often been from the SW or SSW, i.e. a long fetch of warm, moist air from the Azores or the Canary Islands, and hence why it's often been so exceptionally mild (and damp, or even very wet in some areas). Last winter the mean direction was more of a W or WNW, still relatively mild just not as exceptionally so. The same also applies to 2013-2014 with a mean W or WSW flow from the Atlantic.

Dan Holley  9th February 2016