Average Weather in South Portland Maine, United States
In South Portland, the summers are comfortable, the winters are freezing and windy, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 16°F to 78°F and is rarely below 1°F or above 86°F.
Based on the tourism score, the best time of year to visit South Portland for warm-weather activities is from late June to early September.
The warm season lasts for 3.4 months, from June 6 to September 17, with an average daily high temperature above 69°F. The hottest day of the year is July 27, with an average high of 78°F and low of 62°F.
The cold season lasts for 3.3 months, from December 4 to March 14, with an average daily high temperature below 41°F. The coldest day of the year is January 29, with an average low of 16°F and high of 32°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 South Portland, 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 South Portland begins around June 27 and lasts for 4.1 months, ending around October 31. On September 2, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 64% of the time, and overcast or mostly cloudy 36% of the time.
The cloudier part of the year begins around October 31 and lasts for 7.9 months, ending around June 27. On May 17, the cloudiest day of the year, the sky is overcast or mostly cloudy 57% of the time, and clear, mostly clear, or partly cloudy 43% 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 South Portland varies throughout the year.
The wetter season lasts 9.3 months, from March 19 to December 29, with a greater than 27% chance of a given day being a wet day. The chance of a wet day peaks at 33% on June 14.
The drier season lasts 2.7 months, from December 29 to March 19. The smallest chance of a wet day is 22% on February 5.
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 South Portland changes throughout the year.
Rain alone is the most common for 11 months, from February 6 to January 2. The highest chance of a day with rain alone is 33% on June 14.
Snow alone is the most common for 1.1 months, from January 2 to February 6. The highest chance of a day with snow alone is 10% on January 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. South Portland experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in South Portland. The most rain falls during the 31 days centered around October 23, with an average total accumulation of 4.3 inches.
The least rain falls around January 21, with an average total accumulation of 1.5 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. South Portland experiences significant seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 5.6 months, from November 1 to April 20, 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 12, with an average total liquid-equivalent accumulation of 1.4 inches.
The snowless period of the year lasts for 6.4 months, from April 20 to November 1. The least snow falls around July 21, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in South Portland varies significantly over the course of the year. In 2018, the shortest day is December 21, with 8 hours, 56 minutes of daylight; the longest day is June 21, with 15 hours, 27 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 4:58 AM on June 15, and the latest sunrise is 2 hours, 20 minutes later at 7:19 AM on November 3. The earliest sunset is at 4:04 PM on December 10, and the latest sunset is 4 hours, 23 minutes later at 8:26 PM on June 27.
Daylight saving time (DST) is observed in South Portland 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
South Portland experiences some seasonal variation in the perceived humidity.
The muggier period of the year lasts for 2.9 months, from June 19 to September 15, during which time the comfort level is muggy, oppressive, or miserable at least 6% of the time. The muggiest day of the year is July 30, with muggy conditions 26% of the time.
The least muggy day of the year is February 23, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
The average hourly wind speed in South Portland experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 6.1 months, from October 15 to April 19, with average wind speeds of more than 8.0 miles per hour. The windiest day of the year is February 20, with an average hourly wind speed of 10.5 miles per hour.
The calmer time of year lasts for 5.9 months, from April 19 to October 15. The calmest day of the year is July 31, with an average hourly wind speed of 5.5 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in South Portland varies throughout the year.
The wind is most often from the south for 2.4 months, from April 22 to July 2 and for 1.7 weeks, from July 30 to August 11, with a peak percentage of 38% on July 1. The wind is most often from the west for 4.0 weeks, from July 2 to July 30 and for 8.4 months, from August 11 to April 22, with a peak percentage of 40% on July 9.
South Portland is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences significant seasonal variation over the course of the year.
The time of year with warmer water lasts for 2.9 months, from June 29 to September 24, with an average temperature above 58°F. The day of the year with the warmest water is August 9, with an average temperature of 63°F.
The time of year with cooler water lasts for 3.7 months, from January 4 to April 26, with an average temperature below 43°F. The day of the year with the coolest water is March 11, with an average temperature of 38°F.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is in South Portland 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 South Portland for general outdoor tourist activities is from late June to early September, with a peak score in the second week of August.
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 South Portland 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 South Portland typically lasts for 5.7 months (174 days), from around April 25 to around October 16, rarely starting before April 8 or after May 11, and rarely ending before September 30 or after November 2.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in South Portland should appear around May 12, only rarely appearing before May 1 or after May 21.
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 3.5 months, from May 8 to August 23, with an average daily incident shortwave energy per square meter above 5.7 kWh. The brightest day of the year is July 2, with an average of 6.8 kWh.
The darker period of the year lasts for 3.3 months, from November 1 to February 10, with an average daily incident shortwave energy per square meter below 2.5 kWh. The darkest day of the year is December 24, with an average of 1.5 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of South Portland are 43.641 deg latitude, -70.241 deg longitude, and 16 ft elevation.
The topography within 2 miles of South Portland contains only modest variations in elevation, with a maximum elevation change of 164 feet and an average elevation above sea level of 34 feet. Within 10 miles also contains only modest variations in elevation (479 feet). Within 50 miles contains only modest variations in elevation (2,126 feet).
The area within 2 miles of South Portland is covered by artificial surfaces (45%), water (38%), and trees (17%), within 10 miles by water (50%) and trees (24%), and within 50 miles by trees (47%) and water (46%).
This report illustrates the typical weather in South Portland, 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in South Portland.
For each station, the records are corrected for the elevation difference between that station and South Portland 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 South Portland is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between South Portland and a given station.
Time zones for aiports and weather stations are provided by AskGeo.com .