If the high pressure area expands to the south or the south-west, storms can be pulled to the west, hitting Mexico and the northern Gulf coast.

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Usually, the prevailing south-westerly wind would take the ash cloud away from Europe and over the polar region, but a high-pressure area is bringing it over Europe, where it is sitting and barely moving as the ash spreads.

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For what causes the cold snaps is when an area of high pressure sits over the continent and, well, just sits there.

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According to Dr Elsner, this change is related to sudden shifts in the position of the long-term area of high pressure that sits near the Azores.

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National Weather Service meteorologist "Skip" Ely said the dry pattern is caused by a persistent area of high pressure that has dominated North Texas weather since the end of June, blocking normal moisture flows across the South.

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With high pressure now established up from the southwest in the eastern North Atlantic - and an area of low pressure being held further west of Ireland - this year's festival continues on a settled and increasingly warm note.

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Camborne's Trevithick Day is an annual celebration of the heritage and mining heritage of the area, with the focus on its famous son Richard Trevithick, the pioneer of high pressure steam power.

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