May is one of the warmer months of the year in Waltham, with average highs near 18.6°C and lows around 8°C (mean 13.3°C). It is about average for rainfall, averaging 96 mm of rainfall and 79% relative humidity across the period.
May is one of the warmer months of the year in Waltham. Across 45 years of records, the warmest Mays in Waltham were 2012 and 2015 — when the month averaged 15.7°C — while the coldest was 2005 at 10.4°C. Typical May days reach 18.6°C with nights near 8°C. The long-term trend is warming, about 0.3°C per decade.
May is about average for rainfall in Waltham, averaging 96 mm of rainfall. The wettest May on record was 2006 with 284 mm, while the driest was 1993 at 33 mm.
Relative humidity in Waltham during May averages 79%. The most humid May was 2011 at 84%, and the least humid was 2023 at 73%.
May receives about 5.3 kWh/m²/day of solar energy in Waltham. The sunniest May was 2023 at 6.7 kWh/m²/day, and the cloudiest was 1984 at 4.3.
Average wind speed in Waltham during May is 0.4 m/s. The windiest Mays were 2021, 2023 and 2025, among others at 0.5 m/s, while the calmest were 2018, 2022 and 2024, among others at 0.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.0°C | 12.8°C | 12.8°C | 14.2°C | 13.8°C | +0.8°C |
| Avg High | 18.3°C | 18.2°C | 18.1°C | 19.4°C | 19.1°C | +0.8°C |
| Avg Low | 7.6°C | 7.4°C | 7.6°C | 8.9°C | 8.4°C | +0.8°C |
| Avg Rain | 102 mm | 90 mm | 113 mm | 80 mm | 100 mm | -1 mm |
May temperatures in Waltham have risen by about 1.2°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -1.1°C (1992) to a record high of 31.6°C (2016).
Rainfall in May is about average for rainfall, averaging 96 mm, with a wettest year of 284 mm.
A good time to visit Waltham
May is a good time to visit Waltham, with days averaging 18.6°C and nights around 8°C (mean 13.3°C, warmer than Waltham's yearly average) and higher rainfall. July and August are marginally more temperate, but May still suits most travellers.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 18.9°C | 13.9°C | 8.9°C | 26.2°C | 3.5°C | 198 mm | 82% | 0.5 m/s | 4.5 |
| 2024 | 19.7°C | 14.8°C | 9.8°C | 27.0°C | 3.4°C | 123 mm | 83% | 0.4 m/s | 5.2 |
| 2023 | 19.1°C | 13.2°C | 7.2°C | 26.2°C | 0.1°C | 74 mm | 73% | 0.5 m/s | 6.7 |
| 2022 | 20.0°C | 14.7°C | 9.3°C | 29.2°C | 2.3°C | 46 mm | 77% | 0.4 m/s | 6 |
| 2021 | 19.1°C | 13.9°C | 8.7°C | 28.5°C | 3.5°C | 112 mm | 75% | 0.5 m/s | 5.6 |
| 2020 | 18.0°C | 12.4°C | 6.7°C | 26.6°C | 0.2°C | 48 mm | 75% | 0.5 m/s | 6.4 |
| 2019 | 17.3°C | 12.4°C | 7.6°C | 26.2°C | 2.3°C | 83 mm | 81% | 0.5 m/s | 4.8 |
| 2018 | 20.9°C | 15.3°C | 9.8°C | 28.7°C | 4.3°C | 43 mm | 80% | 0.4 m/s | 5.6 |
| 2017 | 17.1°C | 12.5°C | 8.0°C | 28.1°C | 1.3°C | 140 mm | 82% | 0.5 m/s | 4.5 |
| 2016 | 18.5°C | 13.3°C | 8.0°C | 31.6°C | 2.3°C | 60 mm | 78% | 0.4 m/s | 5.2 |
| 2015 | 22.0°C | 15.7°C | 9.5°C | 27.2°C | 4.0°C | 36 mm | 74% | 0.4 m/s | 6.1 |
| 2014 | 18.5°C | 13.4°C | 8.3°C | 25.4°C | 4.0°C | 75 mm | 80% | 0.4 m/s | 5.1 |
| 2013 | 19.8°C | 13.9°C | 8.0°C | 30.1°C | 2.5°C | 112 mm | 78% | 0.5 m/s | 5.8 |
| 2012 🔥 | 20.3°C | 15.7°C | 11.0°C | 28.1°C | 5.7°C | 105 mm | 82% | 0.4 m/s | 4.7 |
| 2011 | 18.8°C | 14.1°C | 9.4°C | 28.3°C | 2.9°C | 71 mm | 84% | 0.4 m/s | 4.8 |
| 2010 | 20.9°C | 15.3°C | 9.7°C | 30.3°C | 0.9°C | 74 mm | 76% | 0.4 m/s | 6.2 |
| 2009 | 18.9°C | 13.8°C | 8.7°C | 27.2°C | 4.3°C | 91 mm | 79% | 0.4 m/s | 5.1 |
| 2008 | 17.5°C | 12.4°C | 7.3°C | 25.2°C | -0.6°C | 46 mm | 76% | 0.5 m/s | 5.6 |
| 2007 | 19.6°C | 13.8°C | 8.0°C | 31.0°C | 1.5°C | 92 mm | 77% | 0.4 m/s | 6.1 |
| 2006 🌧️ | 17.3°C | 12.8°C | 8.2°C | 26.6°C | 3.2°C | 284 mm | 83% | 0.5 m/s | 4.7 |
| 2005 ❄️ | 14.8°C | 10.4°C | 6.1°C | 23.0°C | 1.2°C | 140 mm | 82% | 0.5 m/s | 4.4 |
| 2004 | 19.5°C | 13.9°C | 8.2°C | 27.3°C | 0.8°C | 104 mm | 81% | 0.4 m/s | 5.2 |
| 2003 | 16.9°C | 11.9°C | 6.9°C | 26.1°C | 0.7°C | 102 mm | 82% | 0.4 m/s | 4.5 |
| 2002 | 18.0°C | 12.5°C | 7.1°C | 25.5°C | 1.4°C | 138 mm | 74% | 0.5 m/s | 5.6 |
| 2001 | 19.5°C | 13.8°C | 8.2°C | 28.2°C | 0.7°C | 54 mm | 76% | 0.5 m/s | 5.6 |
| 2000 | 18.5°C | 12.8°C | 7.2°C | 28.0°C | 1.1°C | 83 mm | 80% | 0.4 m/s | 5 |
| 1999 | 20.1°C | 14.1°C | 8.1°C | 29.9°C | 2.1°C | 85 mm | 75% | 0.4 m/s | 5.7 |
| 1998 | 19.6°C | 14.3°C | 9.0°C | 26.7°C | 1.2°C | 140 mm | 82% | 0.5 m/s | 5.6 |
| 1997 | 16.1°C | 11.2°C | 6.3°C | 23.6°C | 0.9°C | 78 mm | 77% | 0.5 m/s | 5.3 |
| 1996 | 17.6°C | 12.3°C | 6.9°C | 26.6°C | 0.8°C | 92 mm | 79% | 0.4 m/s | 5.3 |
| 1995 | 17.3°C | 12.1°C | 6.9°C | 24.1°C | 1.5°C | 66 mm | 78% | 0.4 m/s | 5 |
| 1994 | 17.3°C | 11.9°C | 6.6°C | 25.6°C | 2.0°C | 123 mm | 80% | 0.5 m/s | 5.4 |
| 1993 | 19.2°C | 13.7°C | 8.2°C | 26.2°C | 4.3°C | 33 mm | 78% | 0.4 m/s | 5.3 |
| 1992 | 17.8°C | 11.7°C | 5.6°C | 28.4°C | -1.1°C | 50 mm | 76% | 0.4 m/s | 6.1 |
| 1991 | 21.1°C | 15.4°C | 9.8°C | 27.5°C | 4.4°C | 62 mm | 78% | 0.4 m/s | 5.9 |
| 1990 | 15.9°C | 11.1°C | 6.3°C | 22.1°C | 3.1°C | 165 mm | 80% | 0.5 m/s | 4.8 |
| 1989 | 18.8°C | 13.6°C | 8.4°C | 26.7°C | 4.4°C | 128 mm | 82% | 0.4 m/s | 5 |
| 1988 | 18.0°C | 13.0°C | 7.9°C | 25.0°C | 1.8°C | 108 mm | 83% | 0.4 m/s | 4.9 |
| 1987 | 17.7°C | 12.4°C | 7.0°C | 28.2°C | 1.0°C | 48 mm | 81% | 0.4 m/s | 5.6 |
| 1986 | 18.8°C | 13.3°C | 7.9°C | 27.5°C | -0.3°C | 48 mm | 79% | 0.5 m/s | 5.7 |
| 1985 | 18.4°C | 12.8°C | 7.1°C | 26.9°C | -0.4°C | 97 mm | 76% | 0.5 m/s | 5.7 |
| 1984 | 17.4°C | 12.3°C | 7.2°C | 24.8°C | 0.2°C | 234 mm | 82% | 0.4 m/s | 4.3 |
| 1983 | 17.2°C | 12.2°C | 7.2°C | 23.0°C | 0.7°C | 117 mm | 83% | 0.5 m/s | — |
| 1982 | 19.1°C | 13.7°C | 8.2°C | 25.4°C | 5.2°C | 71 mm | 80% | 0.4 m/s | — |
| 1981 | 19.3°C | 13.5°C | 7.7°C | 26.9°C | 1.2°C | 62 mm | 77% | 0.4 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 18.6°C with lows near 8°C (mean 13.3°C), based on 45 years of NASA POWER data.
May averages 96 mm of rainfall in Waltham, about average for rainfall. The wettest on record was 284 mm in 2006.
The hottest May reached 31.6°C in 2016. The coldest dipped to -1.1°C in 1992.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 1.2°C. Daytime highs moved from 18.3°C to 19.4°C and overnight lows from 7.5°C to 8.8°C over the same span.
May is one of the warmer months of the year in Waltham and about average for rainfall, so plan for around 18.6°C daytime highs and 8°C at night.
Not quite — May is the 8th coolest month in Waltham, averaging 13.3°C.
For May in Waltham, pack light layers you can adjust through the day, with typical highs of 18.6°C and lows of 8°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 79% — quite humid.
Average wind speed in May is 0.4 m/s. The windiest May on record averaged 0.5 m/s (1983).
The wettest May on record was 2006 with 284 mm. On average, May sees 96 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Waltham behaves each May, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for May specifically, along with year-by-year records and how the month has changed over the decades.
