Sarn is among the wettest of UK towns: 1,487 mm (59 in) of rain a year
Sunny July days climb to about 20.6°C (69°F). In January, nights here are milder than in 78% of UK towns. Temperatures cover 18°C across the year, low to high. Expect about 37 frosty starts a year, nights when the air falls below freezing.
Met Office 1991–2020 averages for the town itself.
A year in Sarn at a glance
Each month’s typical high and low, in °C.
What a year in Sarn feels like
Typical highs and lows by season and by month, from the Met Office’s 1991–2020 averages.
About 1,487 mm of rain a year
December is the wettest month and April the driest. About 53 days a year bring 10 mm (0.4 in) or more. 24th wettest of 32 Mid Glamorgan towns of 2,500+.
Rain by month
Millimetres
37 air frosts and 8 days of 25°C a year
On about 37 nights a year the air drops below freezing, and on about under 1 days it stays below freezing all day. About 8 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 18 miles east of Sarn, 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 Sarn 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 |
|---|---|---|---|
| Sarn | 20.6°C | 2.3°C | 1,487 mm |
| Pen-y-fai 1.2 mi | 20.7°C about the same | 2.4°C about the same | 1,376 mm |
| Bettws 1.9 mi | 19.9°C 0.7°C cooler | 2.0°C about the same | 2,029 mm |
| Llangeinor 2.2 mi | 19.9°C 0.7°C cooler | 1.6°C 0.7°C colder | 2,045 mm |
| Bridgend 2.4 mi | 20.7°C about the same | 2.6°C about the same | 1,399 mm |
| Cefn Cribwr 2.9 mi | 20.7°C about the same | 2.7°C about the same | 1,327 mm |
| Pont Rhyd-y-cyff 3.6 mi | 19.7°C 0.8°C cooler | 2.3°C about the same | 1,732 mm |
Sarn 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 | 8.1°C 46°F | 2.3°C 36°F | 5.1°C | 156 mm 6.1 in |
| February | 8.3°C 47°F | 2.3°C 36°F | 5.2°C | 114 mm 4.5 in |
| March | 10.5°C 51°F | 3.4°C 38°F | 7.0°C | 104 mm 4.1 in |
| April | 13.4°C 56°F | 4.9°C 41°F | 9.1°C | 85 mm 3.3 in |
| May | 16.5°C 62°F | 7.5°C 46°F | 12.1°C | 86 mm 3.4 in |
| June | 19.0°C 66°F | 10.4°C 51°F | 14.6°C | 87 mm 3.4 in |
| July | 20.6°C 69°F | 12.3°C 54°F | 16.4°C | 113 mm 4.5 in |
| August | 20.4°C 69°F | 12.1°C 54°F | 16.3°C | 127 mm 5.0 in |
| September | 18.3°C 65°F | 10.2°C 50°F | 14.1°C | 114 mm 4.5 in |
| October | 14.7°C 58°F | 7.6°C 46°F | 11.2°C | 166 mm 6.5 in |
| November | 11.1°C 52°F | 5.0°C 41°F | 8.0°C | 166 mm 6.5 in |
| December | 8.6°C 47°F | 2.8°C 37°F | 5.7°C | 170 mm 6.7 in |
| Year | 14.1°C | 6.7°C | 10.4°C | 1,487 mm |
Where Sarn’s numbers come from
Averages over 30 years, not a forecast.
- Mean temperature, rain and day counts: HadUK-Grid 1991–2020 averages for the 2 Met Office 2 km grid squares whose centre lies inside Sarn’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, 18 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 Sarn’s climate
How warm does Sarn get in summer?
July is the warmest month, with average highs of 20.6°C (69°F). About 8 days a year reach 25°C (77°F), fewer than 62% of UK towns.
How cold does Sarn get in winter?
January nights average 2.3°C (36°F). The air drops below freezing on about 37 nights a year, and about under 1 days a year stay below freezing all day.
How much rain does Sarn get?
About 1,487 mm (59 in) a year, more than 96% of UK towns. December is the wettest month (170 mm) and April the driest (85 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 Sarn. 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 Sarn →
Contains public sector information licensed under the Open Government Licence v3.0. Contains HM Land Registry data © Crown copyright and database right 2026. Contains OS data © Crown copyright and database right 2026 (ONS boundaries). Northern Ireland: Source: NISRA; contains Land & Property Services data and Ordnance Survey of Northern Ireland information, © Crown copyright, licensed under the Open Government Licence v3.0. Scotland: contains National Records of Scotland data, Registers of Scotland data and SEPA data, © Crown copyright / © SEPA 2025, licensed under the Open Government Licence v3.0.