| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 41°F | 32°F | 3.4" |
| February | 21°F | 41°F | 31°F | 3.0" |
| March | 27°F | 48°F | 38°F | 3.8" |
| April | 37°F | 59°F | 48°F | 3.9" |
| May | 46°F | 67°F | 57°F | 3.8" |
| June | 56°F | 77°F | 67°F | 4.4" |
| July | 64°F | 83°F | 73°F | 3.5" |
| August | 61°F | 82°F | 72°F | 3.0" |
| September | 55°F | 76°F | 66°F | 3.9" |
| October | 44°F | 66°F | 55°F | 5.2" |
| November | 34°F | 56°F | 45°F | 3.3" |
| December | 27°F | 47°F | 37°F | 4.8" |
| Index | Riverhead | New York | National |
| Air quality index | 41 | 43 | 42 |
| Pollution index | 14,500,300 | 6,179,275 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 280 |
| Days with moderate air quality | 71 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.080% |
| Mercury | 0.060% |
| City | Population | Air Quality Index | National Avg. |
| Jamesport, NY | 1,046 | 41 | 18.0% |
| Quiogue, NY | 538 | 41 | 18.0% |
| Riverside, NY | 2,610 | 41 | 18.0% |
| Southold, NY | 5,946 | 41 | 18.0% |
| Mattituck, NY | 4,898 | 41 | 18.0% |
| Riverhead, NY | 13,879 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Moorestown-Lenola, NJ | 13,879 | 51 | 2.0% |
| Collingswood, NJ | 13,882 | 51 | 2.0% |
| Chesterton, IN | 13,884 | 37 | 26.0% |
| Brandermill, VA | 13,887 | 44 | 12.0% |
| Lacombe, AB | 13,889 | n/a | |
| Riverhead, NY | 13,879 | 41 | 18.0% |
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