The stratospheric polar vortex above the Northern Hemisphere could weaken unusually early, according to current forecast models. The vortex would normally be strengthening at this time of year, but models suggest a significant decline over the next 10 days.
A major sudden stratospheric warming event is possible, although it remains uncertain whether the westerly winds surrounding the vortex will reverse completely, which is a key requirement for such an event. Sudden stratospheric warming occurs when temperatures high in the stratosphere rise rapidly, sometimes by as much as 50C within a few days, disrupting the vortex’s circulation.
The polar vortex is a large area of low pressure and cold air high above the Arctic. Its strong circulation generally helps keep the coldest air near the pole, but disturbances can allow colder air to move south into the mid-latitudes.
If the vortex weakens substantially, weather patterns could be affected in the following weeks. Persistent areas of high pressure across the mid-latitudes could become more likely, potentially bringing colder and more settled conditions to northern Europe later in the season. However, severe cold is not expected during the next two to three weeks.
The possible disruption comes as an area of low pressure that intensified over the Mediterranean last week is forecast to bring heavy rain and strong winds to central and southern Italy. Warnings have been issued, with more than 100mm of rain expected in 24 hours over higher ground in southern Italy.
The system is forecast to move east across the Ionian Sea and then reach Greece, which is recovering from exceptionally wet and unsettled weather experienced last week.
Sources: The Guardian World.