May is one of the warmer months of the year in Allentown, with average highs near 21.2°C and lows around 9.3°C (mean 15.3°C). It is a relatively wet time of year, averaging 110 mm of rainfall and 79% relative humidity across the period.
May is one of the warmer months of the year in Allentown. Across 45 years of records, the warmest Mays in Allentown were 2004 and 2012 — when the month averaged 18.2°C — while the coldest was 1997 at 12.5°C. Typical May days reach 21.2°C with nights near 9.3°C. The long-term trend is warming, about 0.4°C per decade.
May is a relatively wet time of year in Allentown, averaging 110 mm of rainfall. The wettest May on record was 1989 with 248 mm, while the driest was 2023 at 14 mm.
Relative humidity in Allentown during May averages 79%. The most humid May was 2011 at 84%, and the least humid was 2023 at 71%.
May receives about 5.4 kWh/m²/day of solar energy in Allentown. The sunniest May was 2007 at 6.7 kWh/m²/day, and the cloudiest was 2003 at 3.8.
Average wind speed in Allentown during May is 0.4 m/s. The windiest Mays were 2020, 2021 and 2025, among others at 0.5 m/s, while the calmest were 2022, 2023 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 | 14.7°C | 14.5°C | 15.1°C | 16.4°C | 15.5°C | +0.8°C |
| Avg High | 20.7°C | 20.6°C | 21.1°C | 22.1°C | 21.3°C | +0.6°C |
| Avg Low | 8.6°C | 8.4°C | 9.1°C | 10.8°C | 9.6°C | +1°C |
| Avg Rain | 135 mm | 97 mm | 94 mm | 117 mm | 107 mm | -28 mm |
May temperatures in Allentown have risen by about 1.3°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -2.1°C (2020) to a record high of 32°C (1998).
Rainfall in May is a relatively wet time of year, averaging 110 mm, with a wettest year of 248 mm.
Daytime highs and overnight lows have shifted differently — highs rose about 0.3°C per decade while lows rose 0.5°C per decade, narrowing the gap between day and night.
A good time to visit Allentown
May is a good time to visit Allentown, with days averaging 21.2°C and nights around 9.3°C (mean 15.3°C, warmer than Allentown's yearly average) and higher rainfall. August and June 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 | 21.3°C | 16.0°C | 10.7°C | 27.1°C | 4.5°C | 217 mm | 80% | 0.5 m/s | 4.7 |
| 2024 | 22.7°C | 17.4°C | 12.2°C | 31.7°C | 5.9°C | 89 mm | 82% | 0.4 m/s | 5 |
| 2023 | 21.4°C | 14.6°C | 7.7°C | 27.9°C | 0.6°C | 14 mm | 71% | 0.4 m/s | 6.4 |
| 2022 | 22.2°C | 16.3°C | 10.3°C | 30.5°C | 2.1°C | 145 mm | 80% | 0.4 m/s | 5.2 |
| 2021 | 20.8°C | 14.9°C | 9.0°C | 30.5°C | 2.0°C | 109 mm | 76% | 0.5 m/s | 5.5 |
| 2020 | 19.2°C | 13.5°C | 7.8°C | 27.5°C | -2.1°C | 69 mm | 77% | 0.5 m/s | 5.6 |
| 2019 | 21.8°C | 16.4°C | 11.0°C | 28.0°C | 3.0°C | 206 mm | 82% | 0.5 m/s | 5 |
| 2018 | 23.7°C | 18.0°C | 12.4°C | 31.5°C | 3.0°C | 147 mm | 82% | 0.4 m/s | 4.9 |
| 2017 | 19.9°C | 14.5°C | 9.0°C | 30.7°C | 2.9°C | 130 mm | 79% | 0.5 m/s | 4.7 |
| 2016 | 20.0°C | 14.8°C | 9.5°C | 30.0°C | 0.8°C | 111 mm | 81% | 0.4 m/s | 4.9 |
| 2015 | 24.5°C | 18.0°C | 11.6°C | 30.2°C | 3.4°C | 38 mm | 75% | 0.4 m/s | 6 |
| 2014 | 21.5°C | 15.5°C | 9.6°C | 26.9°C | 4.1°C | 101 mm | 80% | 0.4 m/s | 5.1 |
| 2013 | 21.2°C | 15.2°C | 9.3°C | 30.6°C | -0.3°C | 80 mm | 79% | 0.5 m/s | 5.8 |
| 2012 | 23.7°C | 18.2°C | 12.7°C | 30.4°C | 4.2°C | 153 mm | 81% | 0.4 m/s | 5.1 |
| 2011 | 22.4°C | 17.1°C | 11.8°C | 31.8°C | 4.1°C | 120 mm | 84% | 0.4 m/s | 5 |
| 2010 | 22.7°C | 16.7°C | 10.8°C | 31.2°C | 0.0°C | 84 mm | 78% | 0.5 m/s | 5.6 |
| 2009 | 21.1°C | 15.6°C | 10.0°C | 26.4°C | 3.4°C | 140 mm | 79% | 0.5 m/s | 4.9 |
| 2008 | 19.3°C | 13.4°C | 7.5°C | 27.5°C | 0.0°C | 103 mm | 79% | 0.5 m/s | 5.3 |
| 2007 | 23.0°C | 16.2°C | 9.4°C | 31.7°C | 3.2°C | 49 mm | 75% | 0.4 m/s | 6.7 |
| 2006 | 21.5°C | 15.4°C | 9.2°C | 31.1°C | 2.2°C | 66 mm | 75% | 0.5 m/s | 5.7 |
| 2005 | 18.8°C | 12.8°C | 6.7°C | 26.0°C | 0.1°C | 39 mm | 77% | 0.4 m/s | 5.8 |
| 2004 🔥 | 23.8°C | 18.2°C | 12.6°C | 28.6°C | 3.1°C | 123 mm | 81% | 0.4 m/s | 5.5 |
| 2003 | 18.7°C | 13.8°C | 8.9°C | 25.5°C | 3.3°C | 109 mm | 83% | 0.4 m/s | 3.8 |
| 2002 | 21.1°C | 14.4°C | 7.6°C | 28.9°C | 0.4°C | 121 mm | 74% | 0.5 m/s | 5.8 |
| 2001 | 22.1°C | 15.8°C | 9.5°C | 30.8°C | 3.2°C | 82 mm | 75% | 0.4 m/s | 5.7 |
| 2000 | 21.4°C | 15.6°C | 9.8°C | 30.2°C | 2.1°C | 108 mm | 80% | 0.4 m/s | 5.2 |
| 1999 | 22.5°C | 15.7°C | 8.9°C | 31.6°C | 2.8°C | 55 mm | 72% | 0.5 m/s | 5.8 |
| 1998 | 22.4°C | 16.9°C | 11.4°C | 32.0°C | 5.0°C | 139 mm | 82% | 0.4 m/s | 5.6 |
| 1997 ❄️ | 18.8°C | 12.5°C | 6.2°C | 27.2°C | -0.3°C | 85 mm | 73% | 0.5 m/s | 5.7 |
| 1996 | 19.0°C | 13.2°C | 7.3°C | 29.2°C | 0.2°C | 81 mm | 81% | 0.4 m/s | 5.1 |
| 1995 | 19.9°C | 13.9°C | 8.0°C | 27.2°C | 0.2°C | 82 mm | 78% | 0.5 m/s | 4.9 |
| 1994 | 19.5°C | 13.1°C | 6.7°C | 28.4°C | 1.3°C | 87 mm | 77% | 0.5 m/s | 5.9 |
| 1993 | 21.2°C | 15.2°C | 9.1°C | 27.8°C | 4.2°C | 51 mm | 78% | 0.4 m/s | 5.6 |
| 1992 | 19.7°C | 13.5°C | 7.2°C | 29.1°C | 1.0°C | 127 mm | 78% | 0.5 m/s | 5.2 |
| 1991 | 24.1°C | 17.8°C | 11.5°C | 31.3°C | 3.1°C | 74 mm | 80% | 0.4 m/s | 6.2 |
| 1990 | 19.0°C | 13.3°C | 7.6°C | 25.1°C | 2.4°C | 187 mm | 79% | 0.5 m/s | 4.8 |
| 1989 🌧️ | 19.5°C | 14.0°C | 8.6°C | 27.8°C | 2.6°C | 248 mm | 83% | 0.5 m/s | 4.4 |
| 1988 | 21.0°C | 15.1°C | 9.3°C | 28.6°C | 1.9°C | 161 mm | 82% | 0.4 m/s | 5.2 |
| 1987 | 20.9°C | 14.7°C | 8.6°C | 30.1°C | 0.7°C | 73 mm | 82% | 0.4 m/s | 5.3 |
| 1986 | 21.9°C | 15.6°C | 9.4°C | 28.5°C | -1.7°C | 58 mm | 78% | 0.4 m/s | 6.2 |
| 1985 | 21.9°C | 15.6°C | 9.2°C | 27.6°C | 0.2°C | 139 mm | 77% | 0.5 m/s | 5.8 |
| 1984 | 19.0°C | 13.5°C | 7.9°C | 26.2°C | 1.7°C | 203 mm | 82% | 0.5 m/s | 4.1 |
| 1983 | 19.2°C | 13.4°C | 7.5°C | 24.6°C | -0.4°C | 129 mm | 81% | 0.5 m/s | — |
| 1982 | 21.7°C | 15.6°C | 9.6°C | 26.7°C | 3.9°C | 102 mm | 79% | 0.4 m/s | — |
| 1981 | 21.3°C | 14.5°C | 7.7°C | 27.4°C | 0.1°C | 106 mm | 75% | 0.5 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 21.2°C with lows near 9.3°C (mean 15.3°C), based on 45 years of NASA POWER data.
May averages 110 mm of rainfall in Allentown, a relatively wet time of year. The wettest on record was 248 mm in 1989.
The hottest May reached 32°C in 1998. The coldest dipped to -2.1°C in 2020.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 1.3°C. Daytime highs moved from 20.6°C to 21.7°C and overnight lows from 8.4°C to 10°C over the same span.
May is one of the warmer months of the year in Allentown and a relatively wet time of year, so plan for around 21.2°C daytime highs and 9.3°C at night.
Not quite — May is the 8th coolest month in Allentown, averaging 15.3°C.
For May in Allentown, pack light layers you can adjust through the day, with typical highs of 21.2°C and lows of 9.3°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 (1981).
The wettest May on record was 1989 with 248 mm. On average, May sees 110 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 Allentown 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.
