Cold, wet & unsettled: what's the story with our spring weather?

Analysis: We'll see cooler conditions this weekend with an arctic air mass moving south as March proves to be wetter and duller than average

It's the second half of March, but it doesn't feel very spring-like out there and there's another cool spell on the way this weekend. Paul Moore is a climatologist with Met Eireann and we asked him to explain what exactly is going on with the weather - and if we can expect some spring-like spells before Easter next week.

So what is going on with the weather?

So far, March has been warmer than average, but also wetter and duller. You might say that this is no surprise in a warming world, but this is very interesting because at the same time there's a natural phenomenon happening. A weakened stratospheric polar vortex (SPV) is causing the Jet Stream to be displaced to the south for most of the month, which would normally lead to cooler than average conditions.

Even when the background climatic state would have normally led to cooler than average conditions in Ireland, global warming is overriding this. For example, there have been record high sea surface temperatures across the North Atlantic every day for over a year now. This is making the atmosphere over it warmer but also more moist: when we get a colder air mass descending over us from the north, it will be softened more than in the past.

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From RTÉ Six One News in February 2022, research reveals changes to North Atlantic Jet Stream

Cooler than average conditions can and do still happen, such as at the very beginning of March when we had snow in parts of the country. Again, cooler conditions are forecast this weekend with an arctic air mass moving south over us, but overall these cooler periods are trending shorter and less cold.

How does this compare to previous years?

Based on observations from our 25 primary weather stations, mean temperatures for March are running at between 0.1 °C and 1.6 °C above the 1981-2010 long term average (LTA) reference period, with the warmest temperatures in the South.

Rainfall is also well above average so far, especially in the South and East. A southerly displaced Jetstream also pushes the low pressure systems further south, leading to more rainfall for the South and East of Ireland at times.

From RTÉ Radio 1's Morning Ireland in April 2023, climatologist Paul Moore on how March 2023 was the wettest March on record.

Most stations in the South and East have already had over 100% of the monthly March LTA rainfall with ten days to go until the end of the month. Two stations in Dublin, Phoenix Park and Dublin Airport, have had over 150% of their monthly LTA already, with just a few stations in the Northwest having a drier than average month. We had a wet February and below average sunshine this month so there has been very little drying leading to soil conditions remaining waterlogged over most on the country.

Does this mean our winters are changing?

Ireland is currently seeing warmer and wetter winters compared to previous decades and years. If we compare the averages for the two 30 year reference periods of 1961-1990 and 1991-2020, which were published by Met Éireann in 2023, we can see that Ireland’s climate is warmer and wetter over the most recent 30-year period. The annual mean air temperature has increased by approximately 0.7 °C between the two periods, with all seasons showing an increase in mean air temperatures, including winter. Annual average rainfall has increased by approximately 7% between the two reference periods and again, all seasons are showing a percentage increase in rainfall amounts, including winter.

Winter 2023/24 was mild and wet overall. It was also the 11th consecutive season with above average temperatures in Ireland. All of our 25 primary weather stations saw above average temperatures, ranging between 0.7 °C and 1.7 °C above the 1981-2010 LTA reference period, warmest in the East.

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Rainfall was also above average at most stations for winter, ranging between 96% and 139% of average, wettest in the West. This comes at the end of the third wettest year on record for Ireland since 1941, where 2015 and 2009 were only marginally wetter than 2023.

Is the Irish spring becoming a bit of a late bloomer?

The length of the growing season in Ireland is increasing at the majority of our primary weather stations due to the warming climate, with projections for the growing season in Ireland to both continue to lengthen and to start earlier as the climate warms. Looking at the climate change indices trends in Ireland since 1940 and comparing the two 30 year reference periods of 1961-1990 and 1991-2020 again, we can see that the growing season has lengthened by an average of 14 days at Belmullet, Co Mayo, 16 days at Valentia Observatory, Co Kerry and 16 days at Phoenix Park, Co Dublin between the two reference periods.

At what stage can you say a weather pattern is 'the new norm'?

We are living in a changing climate, as pointed out above, and the climate will to continue to warm and change, at different rates depending on when humans take climate action and the level of that action. If and when we reach net zero, with respect to greenhouse gasses, the global mean temperatures will stabilise within 5-10 years.

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However, this does not mean the temperatures will drop. At that point we will be living in the warmer climate of that particular time, and global mean temperatures will not drop straight away because it takes many thousands of years for carbon dioxide to be flushed out of the atmosphere.

This is why there is such urgency with reaching net zero. When we reach that point, we need that climate to still be one in which we can live. This is not even taking into account the various potential climate tipping points - a critical threshold in a system that becomes irreversible when crossed, leading to a significant change in the state of the system - such as the AMOC (Atlantic Meridional Overturning Circulation) collapse, that become more likely as global mean temperatures rise.

So, any fine, dry, warm-ish weather in sight?

I’m afraid not, at least in the short-term. The weather looks like staying unsettled over the coming week at least, with low pressure in charge. It will turn cooler today (Friday) as a Polar maritime air mass moves down over the country from the northwest. This will bring a few days of sunshine and showers on Friday and Saturday, some of which may turn wintry, before more general rain returns from the west on Sunday. The early days of next week look to continue cool and unsettled.

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The views expressed here are those of the author and do not represent or reflect the views of RTÉ

Cold, wet and unsettled: what's the story with our spring weather?