| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 43°F | 34°F | 3.4" |
| February | 26°F | 44°F | 34°F | 2.8" |
| March | 33°F | 52°F | 41°F | 3.7" |
| April | 43°F | 63°F | 52°F | 3.7" |
| May | 52°F | 71°F | 61°F | 4.2" |
| June | 62°F | 81°F | 71°F | 4.7" |
| July | 69°F | 86°F | 77°F | 4.2" |
| August | 68°F | 85°F | 76°F | 4.8" |
| September | 61°F | 79°F | 69°F | 3.4" |
| October | 51°F | 68°F | 59°F | 4.8" |
| November | 39°F | 57°F | 48°F | 3.0" |
| December | 32°F | 48°F | 40°F | 4.9" |
| Index | Hewlett | New York | National |
| Air quality index | 51 | 43 | 42 |
| Pollution index | 20,796,900 | 6,179,275 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 169 |
| Days with moderate air quality | 180 |
| Days w/ poor A.Q. for sensitive groups | 16 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.130% |
| Carbon Tetrachloride | 0.130% |
| Lead | 0.070% |
| Mercury | 0.060% |
| City | Population | Air Quality Index | National Avg. |
| Cold Spring Harbor, NY | 2,864 | 43 | 14.0% |
| West Hills, NY | 5,225 | 43 | 14.0% |
| Laurel Hollow, NY | 1,967 | 43 | 14.0% |
| Thomaston, NY | 2,602 | 51 | 2.0% |
| Farmingdale, NY | 8,869 | 51 | 2.0% |
| Hewlett, NY | 7,064 | 51 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Cos Cob, CT | 7,065 | 43 | 14.0% |
| Clarkston Heights-Vineland, WA | 7,062 | 29 | 42.0% |
| Delphos, OH | 7,066 | 39 | 22.0% |
| Morrow, GA | 7,061 | 52 | 4.0% |
| Hudson Falls, NY | 7,067 | 35 | 30.0% |
| Hewlett, NY | 7,064 | 51 | 2.0% |
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