Port Jefferson, NY climate
Port Jefferson has chilly, snowy winters and pleasant summers. A typical July afternoon reaches 83°, a January night drops to 24°, and about 32 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Port Jefferson feels like
Winter
Spring
Summer
Fall
Port Jefferson weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 39° | 24° | 3.6" | 10.3" | 11 | 7 | 24° – 38° |
| February | 41° | 25° | 3.2" | 9.4" | 10 | 9 | 21° – 39° |
| March | 48° | 31° | 4.5" | 6.5" | 11 | 4 | 35° – 48° |
| April | 59° | 40° | 4.2" | 0.6" | 11 | 0 | 46° – 54° |
| May | 68° | 50° | 3.6" | 0 | 12 | 0 | 55° – 63° |
| June | 77° | 60° | 4.1" | 0 | 10 | 0 | 65° – 72° |
| July | 83° | 66° | 3.4" | 0 | 9 | 0 | 70° – 78° |
| August | 82° | 65° | 3.8" | 0 | 9 | 0 | 69° – 77° |
| September | 75° | 59° | 4.0" | 0 | 9 | 0 | 64° – 71° |
| October | 64° | 47° | 4.4" | 0 | 9 | 0 | 52° – 62° |
| November | 54° | 38° | 3.6" | 0.5" | 10 | 0 | 41° – 50° |
| December | 44° | 30° | 4.6" | 4.5" | 12 | 3 | 30° – 48° |
| Year | 61° | 45° | 46.9" | 31.8" | 122 | 23 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Port Jefferson
Port Jefferson gets 47 inches of rain and melted snow a year. December is the wettest month and February the driest. Rain or snow falls on about 122 days a year. Snow covers the ground about 23 days of the year.
About 215 frost-free days a year
In half of years the last 32° night comes by April 4 and the first one by November 7. That leaves about 215 frost-free days for gardens, longer than 80% of U.S. towns.
Heating and cooling a home in Port Jefferson
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Port Jefferson, 83% of that work is heating and 17% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
How Port Jefferson compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Port Jefferson averaged 2.3° warmer than the 1900s. The biggest change is in December (+3.6°). The shift is larger than in 99% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Port Jefferson’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. December swings the most: between 1991 and 2020 its average temperature ranged from 30° to 48°. June is the most reliable, staying within 7°.
Common questions about Port Jefferson’s climate
What is the coldest month in Port Jefferson?
January, with a typical high of 39° and a low of 24°.
What is the hottest month in Port Jefferson?
July, with a typical high of 83° and a low of 66°. About 9 days a year reach 90°.
How much snow does Port Jefferson get?
About 32 inches in a normal winter, most of it in January.
When is the first frost in Port Jefferson?
In half of years the first 32° night comes by November 7, and the last spring frost by April 4.
What is the rainiest month in Port Jefferson?
December, with 4.6 inches of rain and melted snow. The year totals 47 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Port Jefferson itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Islip Li Macarthur Airport, NY (11 mi, snow) and Mt Sinai, NY (2 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.