Port San Juan, Alaska climate: Climate normals at a NOAA weather station
Port San Juan's normal year runs from 26°F January nights to 63°F July afternoons, with 137.9 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 4.9°C, January lows of −3°C, July highs of 17°C, 3,502 mm of precipitation a year.
- NOAA stationPort San Juan
- Station IDUSC00507738
- Location60.05°N 148.07°W
- Elevation40 ft (12 m)
On October 23, the normal high in Port San Juan is 43°F and the normal low 34°F, and the chance of measurable rain or snow is 67%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Port San Juan.
- Jan 34° 26°
- Feb 35° 26°
- Mar 36° 26°
- Apr 43° 32°
- May 52° 37°
- Jun 59° 44°
- Jul 63° 50°
- Aug 61° 49°
- Sep 54° 44°
- Oct 45° 36°
- Nov 38° 30°
- Dec 36° 28°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Port San Juan each month?
July is the warmest month, with normal highs of 63°F; January the coldest, with normal lows of 26°F. The most precipitation falls in September (17.38 in), the least in June (4.53 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 34°F | 26°F | 29.9°F | 12.33 | 20 | <1 | 23 | 6 h 40 min |
| February | 35°F | 26°F | 30.5°F | 11.60 | 18 | <1 | 21 | 9 h 10 min |
| March | 36°F | 26°F | 31.2°F | 9.59 | 17 | <1 | 24 | 11 h 40 min |
| April | 43°F | 32°F | 37.1°F | 10.32 | 18 | <1 | 15 | 14 h 30 min |
| May | 52°F | 37°F | 44.5°F | 8.06 | 16 | <1 | 3 | 17 h |
| June | 59°F | 44°F | 51.8°F | 4.53 | 14 | <1 | <1 | 18 h 50 min |
| July | 63°F | 50°F | 56.1°F | 5.25 | 15 | <1 | <1 | 18 h 10 min |
| August | 61°F | 49°F | 55.2°F | 9.79 | 16 | <1 | <1 | 15 h 50 min |
| September | 54°F | 44°F | 48.7°F | 17.38 | 20 | <1 | 1 | 13 h |
| October | 45°F | 36°F | 40.7°F | 17.28 | 21 | <1 | 8 | 10 h 20 min |
| November | 38°F | 30°F | 34.0°F | 15.93 | 19 | <1 | 19 | 7 h 40 min |
| December | 36°F | 28°F | 31.5°F | 15.80 | 22 | <1 | 22 | 6 h |
| Year (annual) | 46°F | 36°F | 40.9°F | 137.86 | 216 | <1 | 136 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 1°C | −3°C | −1.2°C | 313 mm |
| February | 2°C | −3°C | −0.8°C | 295 mm |
| March | 2°C | −3°C | −0.4°C | 244 mm |
| April | 6°C | 0°C | 2.8°C | 262 mm |
| May | 11°C | 3°C | 6.9°C | 205 mm |
| June | 15°C | 7°C | 11.0°C | 115 mm |
| July | 17°C | 10°C | 13.4°C | 133 mm |
| August | 16°C | 10°C | 12.9°C | 249 mm |
| September | 12°C | 6°C | 9.3°C | 441 mm |
| October | 7°C | 2°C | 4.8°C | 439 mm |
| November | 3°C | −1°C | 1.1°C | 405 mm |
| December | 2°C | −2°C | −0.3°C | 401 mm |
NOAA publishes no 1991-2020 snowfall normal for this station, and no record within 25 miles keeps one, so snow is left out here rather than estimated.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00507738; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
Which months are mildest at Port San Juan?
No month's normal high reaches 65°F in Port San Juan: the warmest is July at 63°F.
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00507738.
When is the last frost at Port San Juan?
In Port San Juan, the last spring frost (32°F) comes after May 10 in half of years and after May 28 in one year in ten; the first autumn frost comes before October 7 in half of years and before September 22 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 101 year in 10 after May 28; 9 in 10 after April 26
- First autumn frost, half of years before
- October 71 year in 10 before September 22; 9 in 10 before October 27
NOAA puts the median frost-free season at 150 days, and the season without a hard freeze (28°F) at 186 days.
A hard freeze (28°F) comes after April 23 in half of springs and before October 25 in half of autumns.
By the USDA's method, the average of each year's coldest night over 1991-2020, the station is in plant hardiness zone 7b: the coldest night of a typical year reaches 8°F (24 complete years).
Frost dates for every NOAA station in Alaska · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00507738; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get at Port San Juan?
In a normal year in Port San Juan, a 90°F day is rare, 136 nights fall to 32°F or colder and 216 days bring measurable precipitation.
- Days at 90°F or more
- fewer than 1a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 136a normal year
- Days that stay below freezing
- 33high of 32°F or less
- Days with 0.01 inch of precipitation
- 216a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00507738.
How sunny is it at Port San Juan?
Over a year 59% of the sunlight that would reach the ground under clear skies gets through the clouds at Port San Juan, 2.4 kWh per square metre a day. March is the sunniest month (64%) and November the cloudiest (52%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 53% | 0.3 |
| February | 55% | 0.9 |
| March | 64% | 2.3 |
| April | 61% | 3.6 |
| May | 61% | 4.6 |
| June | 59% | 4.9 |
| July | 60% | 4.6 |
| August | 58% | 3.5 |
| September | 57% | 2.3 |
| October | 53% | 1.1 |
| November | 52% | 0.4 |
| December | 53% | 0.2 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How many heating and cooling degree days does Port San Juan record?
A normal year at Port San Juan brings 8,759 heating degree days, 63% more than the median U.S. place (5,373), and 1 cooling degree days, 100% fewer than the median (908). Eleven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 474 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,087 | 0 |
| February | 966 | 0 |
| March | 1,048 | 0 |
| April | 837 | 0 |
| May | 636 | 0 |
| June | 398 | 0 |
| July | 277 | 1 |
| August | 304 | 0 |
| September | 488 | 0 |
| October | 752 | 0 |
| November | 932 | 0 |
| December | 1,037 | 0 |
| Year (annual) | 8,759 | 1 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00507738. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Have recent years at Port San Juan been warmer than normal?
2025 averaged 42.2°F, 1.3°F above the 1991-2020 normal of 40.9°F. 3 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 39.9°F | −1.0°F | 107.01 |
| 2022 | 41.9°F | +1.0°F | 150.23 |
| 2023 | 40.7°F | −0.2°F | 145.29 |
| 2024 | 41.1°F | +0.2°F | 149.22 |
| 2025 | 42.2°F | +1.3°F | 172.62 |
Source: observed years: ACIS, station USC00507738. A year counts only with all twelve months complete.
How does Port San Juan's climate compare?
Port San Juan is warmer than 65 of the 85 places with their own NOAA record in Alaska, and wetter than 69. Across the 7,247 U.S. stations with normals, its annual mean of 40.9°F is warmer than 7%.
In the Köppen classification computed from these normals, Port San Juan is Dfc: continental, no dry season, cool summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Port San Juan share this climate record?
Chenega has no NOAA station with 1991-2020 normals of its own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Chenega, AK54 people · 4 mi NE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Port San Juan's climate
What is the coldest month at Port San Juan?
January, with a normal high of 34°F and a normal low of 26°F. The warmest is July (63°F by day, 50°F at night).
What is the rainiest month at Port San Juan?
September, with 17.38 in of precipitation in a normal year; the driest is June with 4.53 in.
What plant hardiness zone is Port San Juan in?
By the same method at the station, the coldest night of a typical year reaches 8°F (24 years, 1991-2020): zone 7b.
How late can frost come at Port San Juan?
In half of years the last 32°F night comes after May 10; in one year in ten it comes after May 28. Waiting until May 28 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Alaska climateThe statewide normals and every place in the state
- Main Bay, AK32 miles from this station, 39.5°F a year
- Seward, AK47 miles from this station, 40.4°F a year
- Wally Noerenberg Hatchery, AK52 miles from this station, 40.0°F a year
- Whittier, AK55 miles from this station, 41.1°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made