Portola, California climate: Normal weather by month, frost dates and records
Portola's normal year runs from 19°F December nights to 86°F July afternoons, with 23.3 inches of precipitation and 38 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.2°C, December lows of −7°C, July highs of 30°C, 593 mm of precipitation a year.
- NOAA stationPortola
- Station IDUSC00047085
- Location39.81°N 120.47°W
- Elevation4,850 ft (1,478 m)
- From the center1 miles
- Population2,086
On October 23, the normal high in Portola is 63°F and the normal low 28°F, and the chance of measurable rain or snow is 13%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Portola.
- Jan 43° 19°
- Feb 46° 21°
- Mar 52° 25°
- Apr 58° 29°
- May 67° 35°
- Jun 77° 40°
- Jul 86° 45°
- Aug 85° 43°
- Sep 79° 37°
- Oct 66° 30°
- Nov 53° 24°
- Dec 42° 19°
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 Portola each month?
July is the warmest month, with normal highs of 86°F; December the coldest, with normal lows of 19°F. The most precipitation falls in December (4.28 in), the least in August (0.30 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 43°F | 19°F | 31.1°F | 4.16 | 11.7 | 9 | <1 | 30 | 9 h 40 min |
| February | 46°F | 21°F | 33.7°F | 3.93 | 7.6 | 9 | <1 | 27 | 10 h 40 min |
| March | 52°F | 25°F | 38.4°F | 3.57 | 6.4 | 8 | <1 | 28 | 11 h 50 min |
| April | 58°F | 29°F | 43.4°F | 1.55 | 1.8 | 6 | <1 | 22 | 13 h 10 min |
| May | 67°F | 35°F | 51.0°F | 1.15 | 0.2 | 6 | <1 | 11 | 14 h 20 min |
| June | 77°F | 40°F | 58.7°F | 0.52 | 0.0 | 3 | 2 | 3 | 15 h |
| July | 86°F | 45°F | 65.5°F | 0.34 | 0.0 | 1 | 11 | <1 | 14 h 40 min |
| August | 85°F | 43°F | 63.9°F | 0.30 | 0.0 | 1 | 7 | 1 | 13 h 50 min |
| September | 79°F | 37°F | 58.0°F | 0.44 | 0.1 | 2 | 2 | 6 | 12 h 30 min |
| October | 66°F | 30°F | 48.1°F | 1.07 | 0.4 | 4 | <1 | 22 | 11 h 10 min |
| November | 53°F | 24°F | 38.3°F | 2.03 | 2.4 | 6 | <1 | 27 | 10 h |
| December | 42°F | 19°F | 30.7°F | 4.28 | 7.2 | 8 | <1 | 29 | 9 h 20 min |
| Year (annual) | 63°F | 31°F | 46.7°F | 23.34 | 37.8 | 62 | 22 | 205 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 6°C | −7°C | −0.5°C | 106 mm | 30 cm |
| February | 8°C | −6°C | 0.9°C | 100 mm | 19 cm |
| March | 11°C | −4°C | 3.6°C | 91 mm | 16 cm |
| April | 14°C | −2°C | 6.3°C | 39 mm | 5 cm |
| May | 19°C | 2°C | 10.6°C | 29 mm | 1 cm |
| June | 25°C | 5°C | 14.8°C | 13 mm | 0 cm |
| July | 30°C | 7°C | 18.6°C | 9 mm | 0 cm |
| August | 30°C | 6°C | 17.7°C | 8 mm | 0 cm |
| September | 26°C | 3°C | 14.4°C | 11 mm | 0 cm |
| October | 19°C | −1°C | 8.9°C | 27 mm | 1 cm |
| November | 11°C | −4°C | 3.5°C | 52 mm | 6 cm |
| December | 6°C | −7°C | −0.7°C | 109 mm | 18 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00047085; 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 Portola?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, September has the fewest days with rain (2).
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 USC00047085.
When is the last frost in Portola?
In Portola, the last spring frost (32°F) comes after June 11 in half of years and after July 2 in one year in ten; the first autumn frost comes before September 10 in half of years and before August 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
- June 111 year in 10 after July 2; 9 in 10 after May 25
- First autumn frost, half of years before
- September 101 year in 10 before August 22; 9 in 10 before September 28
NOAA puts the median frost-free season at 91 days, and the season without a hard freeze (28°F) at 136 days.
A hard freeze (28°F) comes after May 17 in half of springs and before October 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Portola in zone 6b in ZIP code 96122, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Portola's NOAA station is in zone 6b: the coldest night of a typical year reaches −1°F (20 complete years).
Frost dates for every NOAA station in California · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00047085; 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 Portola?
In a normal year in Portola, 22 days a year reach 90°F, 205 nights fall to 32°F or colder and 62 days bring measurable precipitation.
- Days at 90°F or more
- 22a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 205a normal year
- Days that stay below freezing
- 10high of 32°F or less
- Days with 0.01 inch of precipitation
- 62a normal year
- Days with 1 inch of snow or more
- 8a normal year
The highest temperature in this station's record (since 1915) is 110°F, on June 30, 1924; the lowest is −24°F, on January 1, 1924.
The wettest calendar year on that record is 2017, with 43.92 in; the snowiest season is 2022–23, with 222.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00047085; records: ACIS (NOAA Regional Climate Centers), station USC00047085. Records use complete months only; a month missing more than three days is left out.
How sunny is Portola?
Over a year 85% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Portola, 5.1 kWh per square metre a day. July is the sunniest month (95%) and December the cloudiest (69%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 73% | 2.4 |
| February | 72% | 3.2 |
| March | 73% | 4.4 |
| April | 77% | 5.8 |
| May | 82% | 7.1 |
| June | 92% | 8.3 |
| July | 95% | 8.3 |
| August | 95% | 7.4 |
| September | 93% | 5.9 |
| October | 87% | 4.2 |
| November | 77% | 2.7 |
| December | 69% | 2.0 |
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 Portola need?
A normal year in Portola brings 6,782 heating degree days, 26% more than the median U.S. place (5,373), and 144 cooling degree days, 84% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 1,616 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,049 | 0 |
| February | 876 | 0 |
| March | 823 | 0 |
| April | 648 | 0 |
| May | 434 | 1 |
| June | 208 | 17 |
| July | 58 | 73 |
| August | 81 | 47 |
| September | 218 | 6 |
| October | 525 | 0 |
| November | 801 | 0 |
| December | 1,062 | 0 |
| Year (annual) | 6,782 | 144 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00047085. 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 Portola been warmer than normal lately?
2024 averaged 48.3°F, 1.6°F above the 1991-2020 normal of 46.7°F.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2024 | 48.3°F | +1.6°F | 25.65 | 115.3 |
Over 54 complete years from 1918 to 2025, the station's annual mean temperature rose at a fitted 2.4°F per century (+0.13°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00047085; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Portola's climate compare?
Portola is warmer than 6 of the other 218 places with their own NOAA record in California, and wetter than 150. Across the 7,247 U.S. stations with normals, its annual mean of 46.7°F is warmer than 26%.
In the Köppen classification computed from these normals, Portola is Dsb: continental, dry-summer, 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 Portola share this climate record?
18 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.
- Delleker, CA668 people · 1 mi NW
- Iron Horse, CA575 people · 2 mi S
- Graeagle, CA532 people · 10 mi W
- Beckwourth, CA442 people · 4 mi NE
- Plumas Eureka, CA412 people · 10 mi W
- Cromberg, CA262 people · 12 mi W
- Mabie, CA113 people · 4 mi SW
- Clio, CA106 people · 6 mi SW
- Gold Mountain, CA91 people · 4 mi SW
- Calpine, CA83 people · 10 mi S
- C-Road, CA60 people · 6 mi SW
- Lake Davis, CA48 people · 3 mi N
- Valley Ranch, CA42 people · 7 mi SW
- Whitehawk, CA40 people · 7 mi SW
- Mohawk Vista, CA29 people · 6 mi W
- Blairsden, CA0 people · 8 mi W
- Johnsville, CA0 people · 12 mi W
- Sattley, CA0 people · 12 mi S
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 Portola's climate
What is the coldest month in Portola?
December, with a normal high of 42°F and a normal low of 19°F. The warmest is July (86°F by day, 45°F at night).
Does it snow in Portola?
Yes: 38 inches in a normal year, falling on 10 days with 0.1 inch or more, the most in January (11.7 inches).
What is the rainiest month in Portola?
December, with 4.28 in of precipitation in a normal year; the driest is August with 0.30 in.
What plant hardiness zone is Portola in?
The USDA's 2023 map puts Portola in zone 6b in ZIP code 96122, the nearest ZIP area. By the same method at Portola's NOAA station, the coldest night of a typical year reaches −1°F (20 years, 1991-2020): zone 6b.
How late can frost come in Portola?
In half of years the last 32°F night comes after June 11; in one year in ten it comes after July 2. Waiting until July 2 leaves about a one-in-ten chance of a later frost.
Nearby and next
- California climateThe statewide normals and every place in the state
- Doyle, CA24 miles from this station, 50.3°F a year
- Downieville, CA25 miles from this station, 53.1°F a year
- Bowman Dam, CA26 miles from this station, 50.4°F a year
- Quincy, CA27 miles from this station, 50.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made