Mountain Ash sits near the top of UK towns for rain, with 2,024 mm (80 in) a year
The coldest hours of a January night bottom out at 1.7°C (35°F) on average. Seasons differ by 18°C, from the coldest nights to the warmest afternoons. In July, afternoons here are cooler than in 77% of UK towns. Comfortable outdoor weather lasts from June to September, with highs of 17–20°C.
Met Office 1991–2020 averages for the town itself.
A year in Mountain Ash at a glance
Each month’s typical high and low, in °C.
What a year in Mountain Ash feels like
Typical highs and lows by season and by month, from the Met Office’s 1991–2020 averages.
About 2,024 mm of rain a year
December is the wettest month and April the driest. About 69 days a year bring 10 mm (0.4 in) or more. 11th wettest of 32 Mid Glamorgan towns of 2,500+.
Rain by month
Millimetres
45 air frosts and 7 days of 25°C a year
On about 45 nights a year the air drops below freezing, and on about 2 days it stays below freezing all day. About 7 days a year reach 25°C (77°F).
Day counts are 1991–2020 averages from the Met Office’s 2 km grid. The Met Office calls a day of 25°C or more a summer day and a night below 0°C an air frost; ground frosts, on grass, come more often.
The Met Office station at Cardiff Bute Park
Cardiff Bute Park is 16 miles south-east of Mountain Ash, 9 m (30 ft) above sea level. It is the nearest of the 37 long-running stations the Met Office publishes in full.
| Month | High | Low | Rain | Air frosts |
|---|---|---|---|---|
| January | 8.6°C | 2.5°C | 127 mm | 8.1 |
| February | 9.1°C | 2.5°C | 93 mm | 7.5 |
| March | 11.3°C | 3.9°C | 85 mm | 3.9 |
| April | 14.4°C | 5.7°C | 72 mm | 1.4 |
| May | 17.4°C | 8.5°C | 78 mm | 0.0 |
| June | 20.1°C | 11.3°C | 73 mm | 0.0 |
| July | 21.8°C | 13.1°C | 84 mm | 0.0 |
| August | 21.4°C | 12.9°C | 105 mm | 0.0 |
| September | 19.1°C | 10.7°C | 87 mm | 0.0 |
| October | 15.2°C | 8.0°C | 128 mm | 1.0 |
| November | 11.6°C | 4.9°C | 131 mm | 3.7 |
| December | 9.1°C | 2.9°C | 140 mm | 8.3 |
| Year | 14.9°C | 7.2°C | 1,201 mm | 34 |
Met Office historic station data, Cardiff Bute Park, 1991–2020 months averaged (a month needs 20 of the 30 years; estimated values counted, missing months left out). Sunshine: Campbell-Stokes recorder.
How Mountain Ash compares
Against the 2,537 towns and cities of 2,500 or more across the UK, each with its own Met Office averages, and its place among Mid Glamorgan towns that size.
Nearby towns’ climate
The nearest towns of 1,000+ within 12 miles: a hill, a valley or the sea can make a real difference over a few miles.
| Town | July high | January low | Rain a year |
|---|---|---|---|
| Mountain Ash | 19.8°C | 1.7°C | 2,024 mm |
| Aberfan 1.7 mi | 19.8°C about the same | 1.6°C about the same | 2,002 mm |
| Abercynon 2.5 mi | 20.3°C 0.5°C warmer | 1.8°C about the same | 1,802 mm |
| Troedyrhiw and Pentrebach 2.9 mi | 19.8°C about the same | 1.6°C about the same | 1,989 mm |
| Treharris 3.2 mi | 20.3°C 0.5°C warmer | 2.2°C 0.6°C milder | 1,780 mm |
| Ferndale 3.2 mi | 19.5°C about the same | 1.2°C 0.5°C colder | 2,382 mm |
| Ynysybwl 3.2 mi | 20.3°C 0.5°C warmer | 1.9°C about the same | 1,800 mm |
Mountain Ash weather by month
Average daily high and low, mean temperature and rain, 1991–2020, for the town itself (the Met Office’s HadUK-Grid).
| Month | High | Low | Mean | Rain |
|---|---|---|---|---|
| January | 7.0°C 45°F | 1.7°C 35°F | 4.3°C | 235 mm 9.2 in |
| February | 7.1°C 45°F | 1.4°C 34°F | 4.2°C | 180 mm 7.1 in |
| March | 9.3°C 49°F | 2.4°C 36°F | 5.9°C | 141 mm 5.5 in |
| April | 12.4°C 54°F | 4.1°C 39°F | 8.3°C | 112 mm 4.4 in |
| May | 15.5°C 60°F | 6.8°C 44°F | 11.2°C | 121 mm 4.7 in |
| June | 18.2°C 65°F | 9.8°C 50°F | 14.0°C | 122 mm 4.8 in |
| July | 19.8°C 68°F | 11.5°C 53°F | 15.7°C | 125 mm 4.9 in |
| August | 19.4°C 67°F | 11.3°C 52°F | 15.5°C | 143 mm 5.6 in |
| September | 17.0°C 63°F | 9.3°C 49°F | 13.2°C | 141 mm 5.5 in |
| October | 13.1°C 56°F | 6.6°C 44°F | 9.9°C | 218 mm 8.6 in |
| November | 9.6°C 49°F | 4.0°C 39°F | 6.8°C | 221 mm 8.7 in |
| December | 7.3°C 45°F | 2.0°C 36°F | 4.6°C | 267 mm 10.5 in |
| Year | 13.0°C | 5.9°C | 9.5°C | 2,024 mm |
Where Mountain Ash’s numbers come from
Averages over 30 years, not a forecast.
- Mean temperature, rain and day counts: HadUK-Grid 1991–2020 averages for the 1 Met Office 2 km grid square whose centre lies inside Mountain Ash’s built-up area.
- Highs and lows: the Met Office publishes average daily maxima and minima on its 12 km grid; each is moved by the difference between the town’s 2 km mean temperature and the 12 km square’s, which carries the town’s own height and setting over.
- Weather station and sunshine: Met Office historic station data for Cardiff Bute Park, 16 miles away, months of 1991–2020 averaged.
- Comparisons: every town and city of 2,500 or more across the UK, all four nations, read the same way.
Met Office HadUK-Grid · Met Office Climate Data Portal · Historic station data. Open Government Licence v3.0.
Questions about Mountain Ash’s climate
How warm does Mountain Ash get in summer?
July is the warmest month, with average highs of 19.8°C (68°F). About 7 days a year reach 25°C (77°F), fewer than 69% of UK towns.
How cold does Mountain Ash get in winter?
February nights average 1.4°C (34°F). The air drops below freezing on about 45 nights a year, and about 2 days a year stay below freezing all day.
How much rain does Mountain Ash get?
About 2,024 mm (80 in) a year, more than almost every UK town. December is the wettest month (267 mm) and April the driest (112 mm).
Where do these figures come from?
The Met Office’s HadUK-Grid 1991–2020 averages, which turn thousands of weather stations into a map of the UK in 2 km squares; the page reads the squares inside Mountain Ash. They are 30-year averages, not a forecast.
Contains Met Office data © Crown copyright 2026, Open Government Licence v3.0. HadUK-Grid 1991–2020 averages via the Met Office Climate Data Portal; station averages from Met Office historic station data. Today’s forecast for Mountain Ash →
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