Sudden Stratospheric Warming: Will It Change March Weather?

Ireland has experienced a notably wet and grey winter, and while meteorological spring begins Sunday, forecasters are closely monitoring activity in the stratospheric polar vortex, with a split-type sudden stratospheric warming occurring in early March.

What is the Stratospheric Polar Vortex?

The stratospheric polar vortex (SPV) is a natural, annual atmospheric phenomenon occurring in the stratosphere over the Polar regions during winter. It’s initiated when decreasing sunlight intensifies the temperature gradient between the cold polar stratosphere and the warmer tropical stratosphere.

During the Northern Hemisphere winter, this increasing temperature gradient creates intense westerly winds circulating the North Pole high in the stratosphere, known as the Polar Night Jet. The SPV strengthens in autumn as the temperature gradient increases and is usually strongest through the winter, separating cold Arctic air from warmer air further south. It naturally breaks down in spring, typically by mid-April, when sunlight returns to the Polar regions.

The strength of the SPV is measured by monitoring the zonal mean zonal wind at 60°N and 10 hPa (about 30km high). The SPV can also weaken or break down during winter due to atmospheric wave breaking, sending energy into the stratosphere and disrupting the flow. A complete breakdown, with westerly winds reversing to easterly, is called a sudden stratospheric warming (SSW).

How Does the Polar Vortex Influence the Jet Stream?

The North Atlantic jet stream largely controls the weather experienced in northwest Europe. It’s lower in the troposphere and can be strongly influenced by activity in the stratosphere during winter.

When the SPV is strong and stable, it can add westerly momentum to the jet stream, keeping it further north and contributing to an active storm season. However, a weakened SPV can lead to a south-shifted jet stream with higher pressure over Polar regions, as has been the case this winter.

You Mentioned a Sudden Stratospheric Warming

A Sudden Stratospheric Warming (SSW) occurs when the SPV breaks down during winter, reversing the zonal wind from westerly to easterly at 60°N and 10 hPa, along with a spike in stratospheric temperatures. This reversal disrupts the flow, and easterly winds can descend through the atmosphere, taking up to two weeks.

The descending easterly flow can weaken the North Atlantic jet stream, causing it to meander and create blocking high-pressure systems. This forces cold air southwards and warm air into the Arctic. The influence of an SPV breakdown can last two to three months.

SSWs can take two forms: displacement of the SPV away from the North Pole, or a split into two separate cores. A split-type SSW is more likely to cause dramatic weather pattern shifts.

What Has Been Happening with the Polar Vortex This Year?

Charts show the strength of the zonal wind at 60°N and 10 hPa. The 2024/25 winter SPV was generally stronger than average but experienced an early breakdown on March 9th, 2025, contributing to a weakening of the jet stream in spring 2025.

This winter, the SPV has been weaker overall and underwent a displacement SSW in late November. This early SSW and subsequent weak SPV contributed to higher pressure over the Arctic and a southern-shifted jet stream, resulting in sustained cold outbreaks over northern Europe and North America, and a lot of rain for the south and east of Ireland during January and February.

Are We Going to See a Sudden Stratospheric Warming?

Forecasts indicate a SSW is expected over the next week to 10 days, likely a split-type SSW. Charts show the SPV already weakened and displaced away from the North Pole. The forecast for March 5th, 2026, shows the SPV split into two cores, with a high-pressure system in between, and the zonal wind has reversed to easterly, confirming the SSW.

What Does This Mean for the Weather in Early March?

While a split-type SSW is expected in early March, its influence on northwest European weather remains uncertain. Global weather patterns are complex and chaotic. However, the SSW increases the likelihood of a change in weather patterns with more high and mid-latitude blocking around mid-March.

Past SSWs have had major influences, such as the “Beast from the East” and Storm Emma in February/March 2018. However, other SSWs have had little impact. Whether easterlies penetrate to the surface in March and the resulting weather will depend on the setup of blocking high-pressure systems and whether it’s a final warming or a SSW with westerly recovery.