Photo: Chiswell Green, The Three Hammers - geograph.org.uk - 566462.jpg : Nigel Cox derivative work: Hogweard · CC BY 2.5More days reach 25 degrees in Chiswell Green than in 80% of UK towns
Midwinter brings lows of about 1.8°C (35°F). Rain is light here, less than falls on 67% of UK towns. Expect the heaviest rain in October and the lightest in March. Homes need heating from November to April, the months averaging under 10°C.
Met Office 1991–2020 averages for the town itself.
A year in Chiswell Green at a glance
Each month’s typical high and low, in °C.
What a year in Chiswell Green feels like
Typical highs and lows by season and by month, from the Met Office’s 1991–2020 averages.
About 697 mm of rain a year
October is the wettest month and March the driest. About 16 days a year bring 10 mm (0.4 in) or more. 13th wettest of 50 Hertfordshire towns of 2,500+.
Rain by month
Millimetres
Sunshine by month
Hours of bright sunshine at Heathrow
42 air frosts and 17 days of 25°C a year
On about 42 nights a year the air drops below freezing, and on about 1 days it stays below freezing all day. About 17 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 Heathrow
Heathrow is 17 miles south of Chiswell Green, 25 m (82 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 | Sun (hours) |
|---|---|---|---|---|---|
| January | 8.4°C | 2.7°C | 59 mm | 6.8 | 59 |
| February | 9.0°C | 2.6°C | 45 mm | 6.2 | 76 |
| March | 11.7°C | 4.1°C | 39 mm | 3.0 | 120 |
| April | 15.0°C | 6.0°C | 42 mm | 0.8 | 169 |
| May | 18.4°C | 9.1°C | 46 mm | 0.0 | 197 |
| June | 21.6°C | 12.0°C | 47 mm | 0.0 | 197 |
| July | 23.9°C | 14.2°C | 46 mm | 0.0 | 206 |
| August | 23.4°C | 14.1°C | 54 mm | 0.0 | 192 |
| September | 20.2°C | 11.6°C | 50 mm | 0.0 | 150 |
| October | 15.8°C | 8.8°C | 65 mm | 0.3 | 111 |
| November | 11.5°C | 5.3°C | 67 mm | 2.7 | 68 |
| December | 8.8°C | 3.1°C | 57 mm | 7.2 | 53 |
| Year | 15.6°C | 7.8°C | 616 mm | 27 | 1,597 |
Met Office historic station data, Heathrow (London Airport), 1991–2020 months averaged (a month needs 20 of the 30 years; estimated values counted, missing months left out). Sunshine: Kipp & Zonen recorder.
How Chiswell Green 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 Hertfordshire 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 |
|---|---|---|---|
| Chiswell Green | 22.5°C | 1.8°C | 697 mm |
| Park Street and Frogmore 0.6 mi | 22.6°C about the same | 1.8°C about the same | 695 mm |
| Bricket Wood 1.4 mi | 22.9°C about the same | 1.8°C about the same | 669 mm |
| London Colney 2.3 mi | 22.6°C about the same | 1.8°C about the same | 692 mm |
| St Albans 2.4 mi | 22.4°C about the same | 1.8°C about the same | 700 mm |
| Radlett 3.1 mi | 23.0°C 0.5°C warmer | 1.6°C about the same | 670 mm |
| Shenley 3.4 mi | 22.7°C about the same | 1.5°C about the same | 695 mm |
Chiswell Green 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 | 7.5°C 45°F | 1.8°C 35°F | 4.7°C | 67 mm 2.7 in |
| February | 8.1°C 47°F | 1.8°C 35°F | 5.0°C | 52 mm 2.1 in |
| March | 10.8°C 51°F | 3.1°C 38°F | 7.0°C | 42 mm 1.7 in |
| April | 13.9°C 57°F | 4.8°C 41°F | 9.4°C | 50 mm 2.0 in |
| May | 17.1°C 63°F | 7.5°C 46°F | 12.3°C | 50 mm 2.0 in |
| June | 20.1°C 68°F | 10.4°C 51°F | 15.3°C | 53 mm 2.1 in |
| July | 22.5°C 72°F | 12.5°C 55°F | 17.5°C | 50 mm 2.0 in |
| August | 22.1°C 72°F | 12.4°C 54°F | 17.3°C | 61 mm 2.4 in |
| September | 19.0°C 66°F | 10.3°C 50°F | 14.6°C | 52 mm 2.0 in |
| October | 14.6°C 58°F | 7.6°C 46°F | 11.1°C | 76 mm 3.0 in |
| November | 10.5°C 51°F | 4.4°C 40°F | 7.4°C | 75 mm 2.9 in |
| December | 7.8°C 46°F | 2.2°C 36°F | 5.0°C | 69 mm 2.7 in |
| Year | 14.5°C | 6.6°C | 10.5°C | 697 mm |
Where Chiswell Green’s numbers come from
Averages over 30 years, not a forecast.
- Mean temperature, rain and day counts: HadUK-Grid 1991–2020 averages for the Met Office 2 km grid square nearest Chiswell Green’s centre (the town is smaller than one square).
- 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 Heathrow (London Airport), 17 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 Chiswell Green’s climate
How warm does Chiswell Green get in summer?
July is the warmest month, with average highs of 22.5°C (72°F). About 17 days a year reach 25°C (77°F), more than 80% of UK towns.
How cold does Chiswell Green get in winter?
January nights average 1.8°C (35°F). The air drops below freezing on about 42 nights a year, and about 1 days a year stay below freezing all day.
How much rain does Chiswell Green get?
About 697 mm (27 in) a year, less than 67% of UK towns. October is the wettest month (76 mm) and March the driest (42 mm).
How sunny is it?
The nearest Met Office station with a sunshine record, Heathrow (17 miles away), averages 1,597 hours of bright sunshine a year. Sunshine isn’t on the town grid, so this is the station’s figure.
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 Chiswell Green. 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 Chiswell Green →
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