Archives For jetstreams

Warm December weather

December 23, 2012 — Leave a comment

Temperatures reached 12C in Reigate yesterday and stayed above 10C overnight. This is very warm for December! The reason is shown in the latest NOAA high resolution satellite taken this 10.15am Sunday. The bank of cloud shows the warm funnel of air brought from the SW by a vigorous jetstream. North of this stationary front are blobs of cumulus cloud shown catching the sunshine. South of the front is a big High pressure giving Spain clear conditions. Also, spot the snow on the Pyrenees. The jetstream turns South over Europe and is bringing cold conditions over places like Greece where snow has fallen over Mount Pelion on the Aegean coast.

Jetstreams are fast moving wind belts up to 9km above the surface. They are located at the “top” of the atmosphere spiraling from west to east around our mid-latitudes at speeds around 200mph. They are important in controlling weather at the surface.
Our own jetstream (the “polar-front jetstream”) usually marks the boundary between tropical air and polar air. This week the jetstream is mostly to the south of the UK and is dragging some big depressions (low pressure areas = storms) across the Atlantic bringing wet and windy weather to Reigate by Wednesday / Thursday.
You can think of jetstreams dragging depressions (storms) along on a tight lead like owners of badly behaved dogs trying to restrain their hounds in the local park. Heel boy!