The short answer
June, then September, then May. If you can only take one week and you want the best odds of seeing the cliffs rather than the inside of a cloud, take the second or third week of June.
That is not because June is dry. Nothing here is dry. It is because June gives you daylight until almost eleven at night, which means a bad morning does not cost you the day. You can lose four hours to weather in June and still get everything done.
Month by month, honestly
We have been here through every version of the Donegal year. This is what each part of it actually delivers.
- March and April
- Cheap, empty and unpredictable. Some coastal restaurants have not reopened. Good for a second visit, wrong for a first.
- May
- Statistically the driest month in the north west and our quiet favourite. Gorse everywhere, everything open, hotel rates still reasonable.
- June
- The best month. Long light, warm enough, and the crowds have not arrived. Book beds by February.
- July and August
- Busiest and most expensive, and Irish family holidays fill the good hotels. Still lovely, but Slieve League has coaches and Rossnowlagh has a car park problem.
- September
- Our recommendation for anyone who can travel outside summer. Warm sea, thinner traffic, prices fall in the second half.
- October
- The red deer rut at Glenveagh, spectacular light, short days. Worth it if you accept dark by seven.
- November to February
- Storm season. Some attractions close, ferries and shuttles stop. Lough Eske Castle in December with the fires lit is a genuinely wonderful thing, but do not plan the coast around it.
What the weather actually does
Donegal does not have seasons in the American sense. It has one long temperate year with more wind in it than you expect. Summer highs sit around nineteen or twenty degrees Celsius, winter lows rarely go below three, and rain arrives in short bursts rather than all day sheets.
The variable that matters is not rainfall, it is cloud base. Slieve League and Errigal make their own weather, and a bright morning in Donegal Town tells you nothing about what Bunglas looks like an hour later. Check the forecast on the morning, not the night before, and keep one flexible half day in every three.
When to book, and what it saves
The county has a small number of good rooms and they do not expand for demand. Lough Eske Castle, Harvey's Point, Rathmullan House and Rosapenna are effectively the whole top tier. For June to August, book by February. For May and September, eight to ten weeks is usually enough.
Moving a trip from the first week of August to the third week of September commonly saves thirty to forty per cent on the same room, and gives you a better county. That single decision is worth more than any other piece of advice on this page.
Timing the trip around one thing
If the trip is about the cliffs, come in June and give Slieve League two possible afternoons rather than one.
If it is about Glenveagh and the deer, come in the first half of October and stay north at Rathmullan House.
If it is about golf, June for daylight and September for ground conditions. If it is about the beaches, and Donegal's beaches are better than most people believe, late August still has warm water and the light stays until nine.