Average Weather in Portola California, United States
In Portola, the summers are warm, arid, and mostly clear and the winters are long, very cold, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 24°F to 83°F and is rarely below 13°F or above 90°F.
Based on the tourism score, the best time of year to visit Portola for warm-weather activities is from early July to late August.
The warm season lasts for 3.0 months, from June 19 to September 18, with an average daily high temperature above 75°F. The hottest day of the year is August 3, with an average high of 83°F and low of 52°F.
The cold season lasts for 3.9 months, from November 18 to March 13, with an average daily high temperature below 49°F. The coldest day of the year is January 2, with an average low of 24°F and high of 41°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In Portola, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Portola begins around May 30 and lasts for 4.6 months, ending around October 18. On July 29, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 89% of the time, and overcast or mostly cloudy 11% of the time.
The cloudier part of the year begins around October 18 and lasts for 7.4 months, ending around May 30. On March 2, the cloudiest day of the year, the sky is overcast or mostly cloudy 58% of the time, and clear, mostly clear, or partly cloudy 41% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Portola varies significantly throughout the year.
The wetter season lasts 5.9 months, from October 28 to April 25, with a greater than 18% chance of a given day being a wet day. The chance of a wet day peaks at 35% on March 1.
The drier season lasts 6.1 months, from April 25 to October 28. The smallest chance of a wet day is 2% on August 11.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation in Portola changes throughout the year.
Rain alone is the most common for 10 months, from February 18 to December 25. The highest chance of a day with rain alone is 18% on November 26.
Mixed snow and rain is the most common for 1.8 months, from December 25 to February 18. The highest chance of a day with mixed snow and rain is 15% on February 6.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Portola experiences significant seasonal variation in monthly rainfall.
The rainy period of the year lasts for 9.0 months, from September 15 to June 15, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around December 7, with an average total accumulation of 4.0 inches.
The rainless period of the year lasts for 3.0 months, from June 15 to September 15. The least rain falls around July 31, with an average total accumulation of 0.1 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Portola experiences significant seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 6.4 months, from October 23 to May 3, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 3, with an average total liquid-equivalent accumulation of 1.2 inches.
The snowless period of the year lasts for 5.6 months, from May 3 to October 23. The least snow falls around August 1, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Portola varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 21 minutes of daylight; the longest day is June 21, with 15 hours, 0 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:33 AM on June 14, and the latest sunrise is 2 hours, 0 minutes later at 7:33 AM on November 3. The earliest sunset is at 4:37 PM on December 7, and the latest sunset is 3 hours, 57 minutes later at 8:34 PM on June 27.
Daylight saving time (DST) is observed in Portola during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.
Sunrise & Sunset with Twilight and Daylight Saving Time
The perceived humidity level in Portola, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.
Humidity Comfort Levels
The average hourly wind speed in Portola experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 6.4 months, from November 7 to May 19, with average wind speeds of more than 5.0 miles per hour. The windiest day of the year is March 21, with an average hourly wind speed of 5.7 miles per hour.
The calmer time of year lasts for 5.6 months, from May 19 to November 7. The calmest day of the year is August 6, with an average hourly wind speed of 4.4 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Portola varies throughout the year.
The wind is most often from the south for 1.7 months, from January 31 to March 22 and for 1.1 months, from November 3 to December 7, with a peak percentage of 42% on February 23. The wind is most often from the west for 6.2 months, from March 22 to September 28, with a peak percentage of 58% on July 23. The wind is most often from the east for 1.2 months, from September 28 to November 3 and for 1.8 months, from December 7 to January 31, with a peak percentage of 36% on October 22.
Best Time of Year to Visit
To characterize how pleasant the weather is in Portola throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Portola for general outdoor tourist activities is from early July to late August, with a peak score in the last week of July.
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Portola for hot-weather activities is from early July to mid August, with a peak score in the last week of July.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
The growing season in Portola typically lasts for 4.5 months (136 days), from around May 28 to around October 12, rarely starting before May 3 or after June 20, and rarely ending before September 16 or after November 3.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in Portola should appear around April 27, only rarely appearing before April 9 or after May 18.
Growing Degree Days
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.4 months, from May 10 to August 23, with an average daily incident shortwave energy per square meter above 7.3 kWh. The brightest day of the year is July 1, with an average of 8.6 kWh.
The darker period of the year lasts for 3.5 months, from November 1 to February 15, with an average daily incident shortwave energy per square meter below 3.4 kWh. The darkest day of the year is December 19, with an average of 2.1 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Portola are 39.810 deg latitude, -120.469 deg longitude, and 5,105 ft elevation.
The topography within 2 miles of Portola contains very significant variations in elevation, with a maximum elevation change of 928 feet and an average elevation above sea level of 5,067 feet. Within 10 miles contains very significant variations in elevation (3,376 feet). Within 50 miles also contains extreme variations in elevation (10,062 feet).
The area within 2 miles of Portola is covered by shrubs (68%) and trees (31%), within 10 miles by trees (52%) and shrubs (33%), and within 50 miles by trees (51%) and shrubs (42%).
This report illustrates the typical weather in Portola, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Portola.
For each station, the records are corrected for the elevation difference between that station and Portola according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Portola is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Portola and a given station.
The stations contributing to this reconstruction are: Reno Stead Airport (40%, 53 kilometers, east); Truckee Tahoe Airport (29%, 62 kilometers, southeast); and Blue Canyon-Nyack Airport (31%, 63 kilometers, south).
Time zones for aiports and weather stations are provided by AskGeo.com .