Early disruption to Arctic winds
The stratospheric polar vortex over the northern hemisphere faces an unusually early weakening. Forecast models suggest it could weaken significantly over the next 10 days. This disruption to the large area of low pressure and cold air high above the Arctic threatens to alter weather patterns across parts of the continent in the coming weeks. A major sudden stratospheric warming event is possible, occurring when temperatures high in the stratosphere rise rapidly, often by as much as 50C in just a few days. This event is associated with a dramatic weakening or reversal of the strong westerly winds surrounding the polar vortex. While a complete reversal of the winds required for a major SSW remains uncertain, the current forecast models strongly favour a significant weakening of the vortex that could influence weather patterns in the following weeks. Such a shift could increase the likelihood of persistent high pressure across the mid-latitudes and colder conditions in northern Europe. A spell of severe cold appears unlikely over the next two to three weeks. This disruption is a notable early-season event for the strong anticlockwise circulation that typically helps contain the coldest air near the pole. The earliest recorded major SSW occurred on 28 November 1968, after records began in 1958.
Mediterranean rain and wind
An area of low pressure that deepened in the Mediterranean Sea last week will bring heavy rain and strong winds to central and southern Italy on Monday. Forecasters expect more than 100mm of rain to fall in just 24 hours across higher ground in southern Italy. This weather system is expected to move eastwards across the Ionian Sea before reaching Greece, a country that is still recovering from exceptionally wet and unsettled weather last week. The potential for colder weather in Europe is clearly the most important consequence of the current atmospheric instability. This movement follows a period of intense weather that has already impacted the Mediterranean. Because the polar vortex usually strengthens during autumn and into winter, a weakening could allow colder air to spill southwards into the mid-latitudes. This change would alter the typical pattern where the strong anticlockwise circulation helps contain the coldest air near the pole.
