Every article about running in Ireland leads with the rain. It is not wrong, exactly — Ireland is genuinely wet — but it is the least useful thing you can be told, because rain is the one weather variable that barely affects how fast you run. What follows is built from eleven years of daily records for Dublin, sampled at the hours people actually set off, and it says something rather different.
The numbers, month by month
Verus keeps an eleven-year archive of conditions for every country it covers, anchored on a real place people run rather than a geographic centroid. For Ireland that anchor is Dublin. Here is what it holds, with London alongside for comparison, because most people reading this are deciding between racing in Ireland and racing at home.
| Month | Dublin high | Dublin low | Dublin rain days | London high | London rain days |
|---|---|---|---|---|---|
| January | 8.3°C | 3.7°C | 12.3 | 7.6°C | 11.6 |
| February | 9.1°C | 4.1°C | 14.0 | 9.1°C | 12.0 |
| March | 10.2°C | 4.6°C | 13.4 | 11.1°C | 11.9 |
| April | 11.8°C | 5.8°C | 12.1 | 14.2°C | 9.2 |
| May | 15.1°C | 8.8°C | 12.0 | 17.6°C | 10.8 |
| June | 17.7°C | 11.5°C | 13.8 | 21.2°C | 10.4 |
| July | 19.3°C | 13.2°C | 14.5 | 22.8°C | 10.4 |
| August | 19.0°C | 13.0°C | 13.8 | 22.4°C | 9.2 |
| September | 16.9°C | 11.2°C | 13.6 | 19.6°C | 11.2 |
| October | 14.1°C | 9.3°C | 13.8 | 15.5°C | 11.4 |
| November | 10.8°C | 6.4°C | 13.8 | 11.1°C | 11.9 |
| December | 9.5°C | 5.2°C | 14.8 | 9.3°C | 11.7 |
Three things fall out of that table, and only one of them is the rain.
Ireland does not really have seasons
Dublin's annual temperature range is 11°C — from an 8.3°C average high in January to 19.3°C in July. London's is 15.2°C. Reykjavík aside, that is about as flat a year as you will find in Europe, and it is the single most important fact about running here.
It means there is no off-season and no unusable month. A British runner writes off August for anything fast and hides indoors in January; an Irish runner does neither, because July in Dublin is cooler than May in London and January is marginally warmer. The Irish racing calendar reflects this — there are serious road races in January and February, which in much of Europe would be unthinkable.
What this means for you
If you are travelling from Britain to race in Ireland in high summer, you are gaining about 3.5°C of cooling on a July or August start line. Over a marathon that is worth real minutes, and it is the main reason Irish summer races are faster than their British equivalents on comparable courses.
Heat is not your problem here
Verus counts "warm mornings" as the share of days in a month that start at or above 24°C — the point where heat stops being a detail and starts setting your pace for you. In eleven years of Dublin records, that figure is zero. Every month. Not low: zero.
Dew point tells the same story. The measure that actually governs how well you shed heat peaks at 12.2°C in August in Dublin. For context, anything below 10°C is air you will not notice, and it takes a dew point above 20°C before evaporative cooling is meaningfully compromised. Ireland never gets close.
So the heat-management advice that dominates running content — dawn starts, electrolyte planning, heat acclimation blocks — is essentially irrelevant here. You can start a race in Ireland at eleven in the morning in July and be fine. That is not true in most of the places British runners fly to.
The rain: 162 days, and mostly not the problem
Dublin records rain on about 162 days a year against London's 132. That is 30 extra wet days, which sounds like a lot and mostly is not, for a simple reason: an Irish rain day is usually a shower, not a downpour. The frequency is high and the intensity is low.
December is the wettest month at 14.8 days and April the driest at 12.1, which is a remarkably narrow spread — there is no dry season to aim for. If you are planning a trip around avoiding rain, you cannot. Plan around something else and accept you will get wet.
Practically, rain costs you very little pace. It costs you comfort, it ruins your feet over a long day if you have not thought about socks, and it makes descents on rock genuinely dangerous — which matters far more on the Wicklow Way or the Kerry hills than it does on a road half marathon.
The wind is the thing nobody warns you about
This is what the rain talk crowds out. Ireland sits on the eastern edge of the Atlantic with nothing between it and Newfoundland, and the prevailing south-westerly is a constant. On the west coast in particular, wind is the dominant variable in how a race goes.
It is not incidental. The Hell of the West triathlon in Kilkee is named for the wind on its bike leg, not for its terrain. Races on the Dingle peninsula, on Achill, along the Connemara coast and around Loop Head are all fundamentally wind races on the day, and a headwind on an exposed coastal road will cost you more than any hill on the route.
Practical
On a coastal Irish race, look at the wind forecast before you look at anything else, and pace the outbound leg conservatively if it is behind you. An out-and-back on the west coast with a strong south-westerly is one of the easiest ways to run a disastrous negative split in reverse.
What to actually wear
The flat temperature range simplifies this enormously. For most of the year, in most of Ireland, the same kit works: shorts, a long-sleeve or a vest depending on the month, and a genuinely windproof layer rather than a waterproof one.
- A windproof beats a waterproof for most Irish running. You will get wet either way; the wind is what actually chills you, and a heavy waterproof just means you get wet from the inside instead.
- Merino or synthetic next to skin, never cotton — you will be damp for the whole run more often than not.
- A cap with a peak does more for you in Irish rain than a hood, which blocks your peripheral vision and flaps in the wind.
- For hill and coastal running, take a proper waterproof anyway. The difference between a shower on the Dublin coast road and a squall on the Wicklow tops is the difference between damp and hypothermic.
- Shoes with real drainage and socks you trust. Wet feet over three hours is a blister problem, not a comfort problem.
When to race here if you are visiting
May and September are the sweet spots — mild, with the longest settled spells and slightly fewer rain days than the depths of winter. But the honest answer is that no month is bad. The Dublin Marathon is deliberately held on the October bank holiday and it works; Dungarvan holds a serious ten-miler in early February and fills it.
If you are coming from Britain specifically for a fast time, come in high summer. The 3.5°C you gain on a July start line is the largest single advantage Ireland offers a visiting runner, and almost nobody thinks to use it.