Photo: Nyttend · Public domainWeather without surprises: Port Jefferson keeps close to the norm for U.S. towns
Nights in January average 19°. Only 65° separates winter nights from summer afternoons. By January nights alone, it runs colder than 63% of U.S. towns. Homes need heating from November to March, the months averaging under 50°.
A year in Port Jefferson at a glance
Each month’s typical high and low, and what it brings.
What stands out about Port Jefferson’s climate
Compared with towns across the U.S., with Port Jefferson’s place in Ohio beside it.
What a year in Port Jefferson feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 175 frost-free days a year
In half of years the last 32° night comes by April 27 and the first by October 20. Frost and day counts come from NOAA’s station at Sidney 1 S, OH, 5 miles from the town’s center, at about the same height.
The 2023 USDA map puts Port Jefferson’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −7°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 42 inches of rain a year
July is the wettest month and February the driest.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Port Jefferson
88% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Sidney 1 S, OH.
Living with Port Jefferson’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
175 frost-free days in zone 6a. The last frost comes by Apr 27 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 20.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October.
Parks & trails →Of the yearly building losses FEMA expects in Port Jefferson from natural hazards, river flooding is the largest share (46%); heat waves, cold waves, winter storms and ice storms together are 6%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Port Jefferson and similar climates
TownRatings has no climate map of the towns around Port Jefferson yet.
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Port Jefferson averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.4°).
A smaller shift than in 66% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Port Jefferson compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Port Jefferson’s place among Ohio’s.
Port Jefferson weather by month
Highs, lows and precipitation from NOAA’s grid at Port Jefferson’s center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 34° | 19° | 3.0" | 18° – 38° |
| February | 38° | 22° | 2.3" | 17° – 40° |
| March | 48° | 30° | 3.2" | 32° – 52° |
| April | 62° | 40° | 4.1" | 44° – 56° |
| May | 72° | 50° | 4.4" | 55° – 68° |
| June | 81° | 60° | 4.5" | 65° – 73° |
| July | 84° | 63° | 4.6" | 68° – 78° |
| August | 82° | 61° | 3.4" | 67° – 76° |
| September | 77° | 54° | 3.2" | 62° – 69° |
| October | 64° | 43° | 2.9" | 49° – 60° |
| November | 50° | 33° | 3.1" | 35° – 48° |
| December | 39° | 25° | 2.9" | 19° – 42° |
| Year | 61° | 42° | 41.5" |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 17° to 40°. September is the most reliable, staying within 8°.
Where Port Jefferson’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Port Jefferson’s center.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Sidney 1 S, OH, 5 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Port Jefferson’s climate
What is the weather like in Port Jefferson?
A typical July afternoon reaches 84°, a January night drops to 19°. Colder January nights than 63% of U.S. towns; cooler July afternoons than 61% of U.S. towns.
How cold does it get in Port Jefferson in winter?
January nights average 19°. About 134 nights a year reach 32° or below and 7 reach 0° or below. In the coldest January of the last 30 years the month averaged 18°.
How hot does it get in Port Jefferson?
July, with a typical high of 84° and a low of 63°. About 14 days a year reach 90° (Sidney 1 S, OH).
When is the first and last frost in Port Jefferson?
In half of years the last spring frost (32°) comes by April 27 and the first fall frost by October 20, about 175 frost-free days, at Sidney 1 S, OH.
What growing zone is Port Jefferson in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −7°.
What is the best time of year to visit Port Jefferson?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Port Jefferson getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 66% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Port Jefferson.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.