Arctic conditions set to continue in Caithness as a result of 'blocked' weather pattern
Arctic temperatures are set to continue in Caithness, according to local weather expert Keith Banks.
He says the current icy conditions are caused by a "blocked" weather pattern linked to a phenomenon known as sudden stratospheric warming (SSW).
"Caithness and other parts of the far north have endured unseasonally cold temperatures, with frosts, coupled with spells of snowfall, having become ubiquitous since the beginning of the year – and there is no prospect of a return to more seasonal weather in the foreseeable future, as the supply of frigid Arctic air continues," said Keith, who writes the John O'Groat Journal's monthly Weather Watch column.
"January 2021 turned out to be Wick's coldest since 1985, with the average temperature in the town last month just 2.20C (36.0F). That's a very significant 1.5C below the long-term average for the time of the year.
"The advent of February has brought no respite from the cold with Wick recording its lowest temperature of the winter so far last night, the mercury bottoming out at a moderately severe 4.9C (23.2F) – the lowest ambient temperature for any February in the town since 2010. Inland locations have been even colder. Last night the temperature at Altnaharra plunged to a numbing minus 12.1C (10.2F).
"The cause of this prolonged and ongoing spell of cold weather has been the culmination of the SSW phenomenon over the North Pole, and this has been enhanced by a continuation of this winter's La Nina event in the Pacific.
"When a major SSW event occurs, a belt of strong westerly winds, known as the polar night jet stream, that encloses and effectively 'quarantines' a large pool of intensely cold air that develops annually above the North Pole during the autumn and winter, that meteorologists call the polar vortex (a large area of low pressure), are greatly weakened or even destroyed by the impacts of surface weather features.
"A wobbling jet stream will eventually cause the stratospheric air to subside and become compressed, and hence substantially warmer, in the space of perhaps only a few days. When this occurs, the intensely cold polar vortex is often split, displaced off the North Pole, and subsequently arrives on reinforced northerly or easterly winds that have gradually descended down through the stratosphere and into the troposphere, where nearly all the weather action we experience occurs.
"The current SSW event has resulted in what is known as a 'blocked' weather pattern, with a large anticyclones situated over north-east Canada and the Greenland region, corresponding with unusually low pressure over northern Europe. The usual path or track of the Atlantic depressions has been displaced far to the south for the time of the year and, as a consequence, winds from the north and the east will continue to import bitterly cold air from the Arctic and Scandinavia.
"Incidentally, it was a similar SSW event that unleashed the 'Beast from the East' across the region at the end of February 2018."