Sudden Stratospheric Warming: What It Means for Ireland’s Weather in March 2026

As Ireland transitions into meteorological spring on March 1st, climatologists are closely monitoring a significant atmospheric event: a split-type sudden stratospheric warming (SSW) occurring in the early days of the month. Following a notably wet and grey winter, understanding the potential impacts of this phenomenon is crucial for anticipating the coming weeks’ weather patterns.

Understanding the Stratospheric Polar Vortex

The stratospheric polar vortex (SPV) is a natural, annual occurrence in the stratosphere above the Polar regions during winter in both hemispheres. It forms when decreasing sunlight reaching the Polar stratosphere intensifies the temperature gradient between the cold polar stratosphere and the warmer tropical stratosphere. This creates a core of intense westerly winds, known as the Polar Night Jet, circulating around the North Pole at an altitude of approximately 60°N.

The SPV strengthens throughout autumn and is typically strongest during the winter months, effectively isolating the very cold Arctic air from warmer air further south. However, the SPV naturally weakens and breaks down each spring, usually around mid-April, as sunlight returns to the Polar regions and warms the atmosphere, reducing the temperature gradient. [RTÉ]

How Does the SPV Influence Our Weather?

The North Atlantic jet stream, a key driver of weather patterns in northwest Europe, is significantly influenced by the state of the SPV. A strong and stable SPV generally reinforces westerly momentum in the jet stream, keeping it further north and contributing to an active storm season. However, a weakened SPV can cause the jet stream to shift southward, leading to higher-than-normal pressure over the Polar regions. [RTÉ]

What is a Sudden Stratospheric Warming?

A sudden stratospheric warming (SSW) occurs when the SPV breaks down during the winter months, often due to atmospheric wave breaking in the troposphere sending energy upwards into the stratosphere, rapidly raising temperatures and disrupting the flow. This reversal of winds from westerly to easterly high in the stratosphere can have cascading effects on the atmosphere below. [MIPA Overseas]

There are two primary types of SSW:

• Displacement SSW: The SPV is displaced away from the North Pole, weakening as it moves away from its primary energy source.
• Split SSW: The SPV splits into two separate cores, pushed away from the North Pole in different directions. A split-type SSW is generally associated with more dramatic shifts in weather patterns for northwest Europe. [RTÉ]

The 2025/2026 Stratospheric Polar Vortex

The winter of 2024/2025 saw a generally stronger-than-average SPV, followed by an early breakdown in March 2025. This contributed to a weakening of the North Atlantic jet stream during spring 2025. The current winter (2025/2026) has been characterized by a much weaker SPV, experiencing a displacement SSW in late November. This early SSW and subsequent weakness contributed to higher pressure over the Arctic and a southward-shifted jet stream, resulting in sustained cold outbreaks in northern Europe and North America and a particularly wet January and February for the south and east of Ireland. [RTÉ]

Current Forecast: A Split-Type SSW

Forecasts indicate that a split-type SSW is now expected to occur over the next week to 10 days. This is based on observations of the zonal wind at 60°N and at 10 hPa, which has already dropped below average for late February and is forecast to continue decreasing. [RTÉ]

What Does This Mean for Ireland’s Weather in March?

While a split-type SSW is anticipated in early March, the precise impact on Ireland’s weather remains uncertain. Global weather patterns are complex and influenced by numerous interacting factors. However, this SSW increases the likelihood of a change in weather patterns, with potential for increased high-latitude blocking from mid-March onwards. [RTÉ]

Past SSW events have had varying effects, ranging from cold snaps like the “Beast from the East” in 2018 to minimal impact. The ultimate weather outcome will depend on whether the easterly flow penetrates to the surface and how blocking high-pressure systems develop. [RTÉ]