Petersburg, Alaska climate: Normal weather by month, frost dates and records
Petersburg's normal year runs from 27°F January nights to 62°F July afternoons, with 110.2 inches of precipitation and 86 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 6.1°C, January lows of −3°C, July highs of 17°C, 2,799 mm of precipitation a year.
- NOAA stationPetersburg 1
- Station IDUSW00025329
- Location56.81°N 132.94°W
- Elevation107 ft (33 m)
- Population (census place)3,346
On October 23, the normal high in Petersburg is 45°F and the normal low 37°F, and the chance of measurable rain or snow is 76%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Petersburg.
- Jan 35° 27°
- Feb 37° 28°
- Mar 40° 30°
- Apr 48° 35°
- May 55° 42°
- Jun 60° 48°
- Jul 62° 51°
- Aug 61° 50°
- Sep 56° 46°
- Oct 47° 39°
- Nov 39° 32°
- Dec 35° 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 in Petersburg each month?
July is the warmest month, with normal highs of 62°F; January the coldest, with normal lows of 27°F. The most precipitation falls in September (14.35 in), the least in June (4.98 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 35°F | 27°F | 30.9°F | 11.39 | 20.7 | 21 | <1 | 21 | 7 h 20 min |
| February | 37°F | 28°F | 32.1°F | 7.60 | 16.9 | 17 | <1 | 20 | 9 h 30 min |
| March | 40°F | 30°F | 34.9°F | 7.60 | 20.0 | 20 | <1 | 21 | 11 h 40 min |
| April | 48°F | 35°F | 41.4°F | 6.66 | 1.1 | 18 | <1 | 10 | 14 h 10 min |
| May | 55°F | 42°F | 48.5°F | 5.86 | 0.2 | 16 | <1 | 2 | 16 h 20 min |
| June | 60°F | 48°F | 54.0°F | 4.98 | 0.0 | 16 | <1 | <1 | 17 h 50 min |
| July | 62°F | 51°F | 56.3°F | 5.63 | 0.0 | 17 | <1 | <1 | 17 h 20 min |
| August | 61°F | 50°F | 55.8°F | 8.21 | 0.0 | 17 | <1 | <1 | 15 h 20 min |
| September | 56°F | 46°F | 50.8°F | 14.35 | 0.0 | 20 | <1 | <1 | 12 h 50 min |
| October | 47°F | 39°F | 43.3°F | 13.84 | 0.4 | 23 | <1 | 5 | 10 h 30 min |
| November | 39°F | 32°F | 35.8°F | 12.28 | 10.8 | 23 | <1 | 15 | 8 h 10 min |
| December | 35°F | 28°F | 31.8°F | 11.79 | 15.5 | 21 | <1 | 21 | 6 h 50 min |
| Year (annual) | 48°F | 38°F | 43.0°F | 110.19 | 85.6 | 229 | <1 | 115 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 1°C | −3°C | −0.6°C | 289 mm | 53 cm |
| February | 3°C | −2°C | 0.1°C | 193 mm | 43 cm |
| March | 5°C | −1°C | 1.6°C | 193 mm | 51 cm |
| April | 9°C | 2°C | 5.2°C | 169 mm | 3 cm |
| May | 13°C | 5°C | 9.2°C | 149 mm | 1 cm |
| June | 16°C | 9°C | 12.2°C | 126 mm | 0 cm |
| July | 17°C | 11°C | 13.5°C | 143 mm | 0 cm |
| August | 16°C | 10°C | 13.2°C | 209 mm | 0 cm |
| September | 13°C | 8°C | 10.4°C | 364 mm | 0 cm |
| October | 9°C | 4°C | 6.3°C | 352 mm | 1 cm |
| November | 4°C | 0°C | 2.1°C | 312 mm | 27 cm |
| December | 2°C | −2°C | −0.1°C | 299 mm | 39 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00025329; 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.
When is the best weather to visit Petersburg?
No month's normal high reaches 65°F in Petersburg: the warmest is July at 62°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 USW00025329.
When is the last frost in Petersburg?
In Petersburg, the last spring frost (32°F) comes after April 29 in half of years and after May 14 in one year in ten; the first autumn frost comes before October 17 in half of years and before September 30 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
- April 291 year in 10 after May 14; 9 in 10 after April 15
- First autumn frost, half of years before
- October 171 year in 10 before September 30; 9 in 10 before November 1
NOAA puts the median frost-free season at 169 days, and the season without a hard freeze (28°F) at 204 days.
A hard freeze (28°F) comes after April 11 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Petersburg in zone 7b in ZIP code 99833, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Petersburg's NOAA station is in zone 7a: the coldest night of a typical year reaches 3°F (19 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Alaska · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00025329; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; 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 in Petersburg?
In a normal year in Petersburg, a 90°F day is rare, 115 nights fall to 32°F or colder and 229 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
- 115a normal year
- Days that stay below freezing
- 28high of 32°F or less
- Days with 0.01 inch of precipitation
- 229a normal year
- Days with 1 inch of snow or more
- 24a normal year
The highest temperature in this station's record (since 1926) is 84°F, on July 17, 1927; the lowest is −19°F, on January 30, 1947.
The wettest calendar year on that record is 2015, with 135.98 in; the snowiest season is 1971–72, with 221.6 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00025329; records: ACIS (NOAA Regional Climate Centers), station USW00025329. Records use complete months only; a month missing more than three days is left out.
How sunny is Petersburg?
Over a year 57% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Petersburg, 2.4 kWh per square metre a day. May is the sunniest month (62%) and November the cloudiest (48%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 48% | 0.5 |
| February | 58% | 1.2 |
| March | 58% | 2.3 |
| April | 61% | 3.6 |
| May | 62% | 4.6 |
| June | 57% | 4.7 |
| July | 54% | 4.1 |
| August | 57% | 3.5 |
| September | 54% | 2.4 |
| October | 52% | 1.3 |
| November | 48% | 0.6 |
| December | 48% | 0.3 |
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 much heating and cooling does Petersburg need?
A normal year in Petersburg brings 8,018 heating degree days, 49% more than the median U.S. place (5,373), and 1 cooling degree days, 100% fewer than the median (908). Ten months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 610 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,057 | 0 |
| February | 921 | 0 |
| March | 932 | 0 |
| April | 707 | 0 |
| May | 512 | 0 |
| June | 331 | 1 |
| July | 268 | 0 |
| August | 287 | 0 |
| September | 428 | 0 |
| October | 673 | 0 |
| November | 876 | 0 |
| December | 1,028 | 0 |
| Year (annual) | 8,018 | 1 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00025329. 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.
Has Petersburg been warmer than normal lately?
2025 averaged 43.0°F, equal to the 1991-2020 normal of 43.0°F.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2025 | 43.0°F | at normal | 133.90 | 75.8 |
Over 56 complete years from 1930 to 2025, the station's annual mean temperature rose at a fitted 2.0°F per century (+0.11°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00025329; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Petersburg's climate compare?
Petersburg is warmer than 74 of the other 84 places with their own NOAA record in Alaska, and wetter than 68. Across the 7,247 U.S. stations with normals, its annual mean of 43.0°F is warmer than 12%.
In the Köppen classification computed from these normals, Petersburg is Dfb: continental, no dry season, warm 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 Petersburg share this climate record?
3 places have no NOAA station with 1991-2020 normals of their 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.
- Kake, AK541 people · 38 mi W
- Kupreanof, AK19 people · 2 mi NW
- Hobart Bay, AK0 people · 44 mi N
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 Petersburg's climate
What is the coldest month in Petersburg?
January, with a normal high of 35°F and a normal low of 27°F. The warmest is July (62°F by day, 51°F at night).
Does it snow in Petersburg?
Yes: 86 inches in a normal year, falling on 36 days with 0.1 inch or more, the most in January (20.7 inches).
What is the rainiest month in Petersburg?
September, with 14.35 in of precipitation in a normal year; the driest is June with 4.98 in.
What plant hardiness zone is Petersburg in?
The USDA's 2023 map puts Petersburg in zone 7b in ZIP code 99833, the nearest ZIP area. By the same method at Petersburg's NOAA station, the coldest night of a typical year reaches 3°F (19 years, 1991-2020): zone 7a.
How late can frost come in Petersburg?
In half of years the last 32°F night comes after April 29; in one year in ten it comes after May 14. Waiting until May 14 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Alaska climateThe statewide normals and every place in the state
- Wrangell, AK31 miles from this station, 44.9°F a year
- Point Baker, AK41 miles from this station, 43.7°F a year
- Little Port Walter, AK71 miles from this station, 44.1°F a year
- Port Alexander, AK76 miles from this station, 45.6°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made