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Climate and Average Weather Year Round in Portland Maine, United States

In Portland, the summers are comfortable; the winters are freezing, snowy, 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 87°F.

Based on the tourism score, the best time of year to visit Portland for warm-weather activities is from late June to early September.

Climate in Portland

very coldcoldcoolwarmcoolcoldvery coldJanFebMarAprMayJunJulAugSepOctNovDecNowNow64%64%43%43%clearovercastprecipitation: 4.3 inprecipitation: 4.3 in2.9 in2.9 inmuggy: 26%muggy: 26%0%0%drydrytourism score: 6.9tourism score: 6.90.00.0
Portland weather by month. Click on each chart for more information.

The warm season lasts for 3.4 months, from June 4 to September 16, with an average daily high temperature above 69°F. The hottest month of the year in Portland is July, with an average high of 78°F and low of 61°F.

The cold season lasts for 3.3 months, from December 3 to March 13, with an average daily high temperature below 41°F. The coldest month of the year in Portland is January, with an average low of 17°F and high of 32°F.

Average High and Low Temperature in Portland

Average High and Low Temperature in PortlandwarmcoldcoldJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F10°F10°F20°F20°F30°F30°F40°F40°F50°F50°F60°F60°F70°F70°F80°F80°F90°F90°F100°F100°FJan 2932°FJan 2932°FJul 2578°FJul 2578°F16°F16°F62°F62°FJun 469°FJun 469°FSep 1669°FSep 1669°FDec 341°FDec 341°FMar 1341°FMar 1341°F52°F52°F53°F53°F27°F27°F26°F26°FNowNow
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.
AverageJanFebMarAprMayJunJulAugSepOctNovDec
High 32°F34°F42°F53°F63°F72°F78°F76°F69°F58°F47°F37°F
Temp. 24°F26°F34°F44°F54°F63°F69°F68°F61°F50°F40°F30°F
Low 17°F19°F27°F37°F46°F55°F61°F60°F53°F42°F33°F23°F

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 Portland

Average Hourly Temperature in PortlandJanFebMarAprMayJunJulAugSepOctNovDec12 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNowNowfreezingfreezingvery coldvery coldcoldcoldcoolcomfortablewarmcomfortable
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Gevaş, Turkey (5,416 miles away) is the far-away foreign place with temperatures most similar to Portland (view comparison).

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In 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 Portland begins around June 27 and lasts for 4.1 months, ending around October 30.

The clearest month of the year in Portland is September, during which on average the sky is clear, mostly clear, or partly cloudy 62% of the time.

The cloudier part of the year begins around October 30 and lasts for 7.9 months, ending around June 27.

The cloudiest month of the year in Portland is May, during which on average the sky is overcast or mostly cloudy 56% of the time.

Cloud Cover Categories in Portland

Cloud Cover Categories in PortlandclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Sep 164%Sep 164%May 1643%May 1643%Jun 2753%Jun 2753%Oct 3054%Oct 3054%NowNowclearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.
FractionJanFebMarAprMayJunJulAugSepOctNovDec
Cloudier 52%52%54%55%56%50%43%39%38%43%50%53%
Clearer 48%48%46%45%44%50%57%61%62%57%50%47%

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Portland varies throughout the year.

The wetter season lasts 9.2 months, from March 19 to December 25, with a greater than 28% chance of a given day being a wet day. The month with the most wet days in Portland is July, with an average of 10.0 days with at least 0.04 inches of precipitation.

The drier season lasts 2.8 months, from December 25 to March 19. The month with the fewest wet days in Portland is February, with an average of 6.8 days with at least 0.04 inches of precipitation.

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 Portland changes throughout the year.

Rain alone is the most common for 11 months, from February 10 to December 31. The month with the most days of rain alone in Portland is July, with an average of 10.0 days.

Snow alone is the most common for 1.3 months, from January 1 to February 10. The month with the most days of snow alone in Portland is January, with an average of 3.1 days.

Daily Chance of Precipitation in Portland

Daily Chance of Precipitation in PortlandsnowrainJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Jun 1333%Jun 1333%Feb 522%Feb 522%Mar 1928%Mar 1928%Dec 2528%Dec 2528%NowNowsnowrainmixed
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).
Days ofJanFebMarAprMayJunJulAugSepOctNovDec
Rain 2.3d2.7d5.1d7.5d9.2d9.6d10.0d8.6d8.0d8.4d7.1d4.5d
Mixed 2.0d1.7d1.9d0.7d0.0d0.0d0.0d0.0d0.0d0.1d0.9d1.9d
Snow 3.1d2.4d1.1d0.2d0.0d0.0d0.0d0.0d0.0d0.0d0.4d2.4d
Any 7.4d6.8d8.1d8.4d9.3d9.6d10.0d8.6d8.0d8.6d8.5d8.8d

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. Portland experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Portland. The month with the most rain in Portland is October, with an average rainfall of 4.2 inches.

The month with the least rain in Portland is January, with an average rainfall of 1.5 inches.

Average Monthly Rainfall in Portland

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average snowfall.
JanFebMarAprMayJunJulAugSepOctNovDec
Rainfall 1.5″2.0″2.9″3.7″3.5″3.4″3.0″2.9″3.4″4.2″3.9″2.6″

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Portland experiences extreme seasonal variation in monthly snowfall.

The snowy period of the year lasts for 5.6 months, from October 30 to April 19, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Portland is January, with an average snowfall of 14.7 inches.

The snowless period of the year lasts for 6.4 months, from April 19 to October 30. The least snow falls around July 20, with an average total accumulation of 0.0 inches.

Average Monthly Snowfall in Portland

Average Monthly Snowfall in PortlandsnowsnowJanFebMarAprMayJunJulAugSepOctNovDec0 in0 in5 in5 in10 in10 in15 in15 in20 in20 in25 in25 in30 in30 inJan 1114.7 inJan 1114.7 inJul 200.0 inJul 200.0 inOct 301.0 inOct 301.0 inApr 191.0 inApr 191.0 in
The average snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.
JanFebMarAprMayJunJulAugSepOctNovDec
Snowfall 14.7″11.7″7.0″1.4″0.0″0.0″0.0″0.0″0.0″0.3″2.9″11.4″

The length of the day in Portland varies significantly over the course of the year. In 2024, the shortest day is December 21, with 8 hours, 56 minutes of daylight; the longest day is June 20, with 15 hours, 27 minutes of daylight.

Hours of Daylight and Twilight in Portland

Hours of Daylight and Twilight in PortlandJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 8 minMar 1912 hr, 8 minMar 1915 hr, 27 minJun 2015 hr, 27 minJun 2012 hr, 12 minSep 2212 hr, 12 minSep 228 hr, 56 minDec 218 hr, 56 minDec 21nightnightdayNowNow
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.
Hours ofJanFebMarAprMayJunJulAugSepOctNovDec
Daylight 9.4h10.5h12.0h13.5h14.8h15.4h15.0h13.9h12.5h11.0h9.7h9.0h

The earliest sunrise is at 4:58 AM on June 14, and the latest sunrise is 2 hours, 20 minutes later at 7:18 AM on November 2. The earliest sunset is at 4:03 PM on December 9, and the latest sunset is 4 hours, 23 minutes later at 8:26 PM on June 26.

Daylight saving time (DST) is observed in Portland during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.

Sunrise & Sunset with Twilight and Daylight Saving Time in Portland

Sunrise & Sunset with Twilight and Daylight Saving Time in PortlandJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 144:58 AMJun 144:58 AM8:26 PMJun 268:26 PMJun 26Dec 94:03 PMDec 94:03 PM7:18 AMNov 27:18 AMNov 2Mar 10DSTMar 10DSTDSTNov 3DSTNov 3daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunsetNowNow
The solar day over the course of the year 2024. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

Solar Elevation and Azimuth in Portland

Solar Elevation and Azimuth in PortlandJanFebMarAprMayJunJulAugSepOctNovDec12 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AM000101010102020203030304040506000010101020202020303040405050602370NowNow
northeastsouthwest
Solar elevation and azimuth over the course of the year 2024. The black lines are lines of constant solar elevation (the angle of the sun above the horizon, in degrees). The background color fills indicate the azimuth (the compass bearing) of the sun. The lightly tinted areas at the boundaries of the cardinal compass points indicate the implied intermediate directions (northeast, southeast, southwest, and northwest).

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

Moon Rise, Set & Phases in Portland

The time in which the moon is above the horizon (light blue area), with new moons (dark gray lines) and full moons (blue lines) indicated. The shaded overlays indicate night and civil twilight.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

Portland experiences some seasonal variation in the perceived humidity.

The muggier period of the year lasts for 2.9 months, from June 17 to September 14, during which time the comfort level is muggy, oppressive, or miserable at least 6% of the time. The month with the most muggy days in Portland is July, with 6.6 days that are muggy or worse.

The least muggy day of the year is February 23, when muggy conditions are essentially unheard of.

Humidity Comfort Levels in Portland

Humidity Comfort Levels in PortlandmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Feb 230%Feb 230%Jul 2926%Jul 2926%Jun 176%Jun 176%Sep 146%Sep 146%NowNowmuggymuggycomfortablecomfortabledrydryhumidhumidoppressiveoppressive
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.
JanFebMarAprMayJunJulAugSepOctNovDec
Muggy days 0.0d0.0d0.0d0.0d0.1d1.9d6.6d6.0d1.7d0.1d0.0d0.0d

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Portland experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 6.1 months, from October 14 to April 19, with average wind speeds of more than 7.8 miles per hour. The windiest month of the year in Portland is February, with an average hourly wind speed of 10.1 miles per hour.

The calmer time of year lasts for 5.9 months, from April 19 to October 14. The calmest month of the year in Portland is July, with an average hourly wind speed of 5.5 miles per hour.

Average Wind Speed in Portland

Average Wind Speed in PortlandwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph0 mph2 mph2 mph4 mph4 mph6 mph6 mph8 mph8 mph10 mph10 mph12 mph12 mph14 mph14 mph16 mph16 mphFeb 2010.2 mphFeb 2010.2 mphJul 305.3 mphJul 305.3 mphOct 147.8 mphOct 147.8 mphApr 197.8 mphApr 197.8 mphNowNow
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Wind Speed (mph) 10.010.19.57.96.65.95.55.66.57.88.79.4

The predominant average hourly wind direction in Portland varies throughout the year.

The wind is most often from the south for 2.3 months, from April 22 to July 1, with a peak percentage of 38% on June 30. The wind is most often from the west for 9.7 months, from July 1 to April 22, with a peak percentage of 47% on January 1.

Wind Direction in Portland

Wind Direction in PortlandWSWJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%NowNowwestsouthnortheast
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

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 28 to September 23, with an average temperature above 58°F. The month of the year in Portland with the warmest water is August, with an average temperature of 62°F.

The time of year with cooler water lasts for 3.7 months, from January 4 to April 25, with an average temperature below 43°F. The month of the year in Portland with the coolest water is March, with an average temperature of 38°F.

Average Water Temperature in Portland

Average Water Temperature in PortlandwarmcoolJanFebMarAprMayJunJulAugSepOctNovDec35°F35°F40°F40°F45°F45°F50°F50°F55°F55°F60°F60°F65°F65°F70°F70°FAug 963°FAug 963°F38°FMar 938°FMar 9Jun 2858°FJun 2858°FSep 2358°FSep 2358°FJan 443°FJan 443°FApr 2543°FApr 2543°FNowNow
The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.
WaterJanFebMarAprMayJunJulAugSepOctNovDec
Temperature 42°F39°F38°F41°F47°F55°F61°F62°F59°F54°F49°F45°F

To characterize how pleasant the weather is in 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 Portland for general outdoor tourist activities is from late June to early September, with a peak score in the second week of August.

Tourism Score in Portland

Tourism Score in Portlandbest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810106.96.90.00.0NowNowtemperaturetemperature cloudscloudsprecipitationprecipitationtourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

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 Portland for hot-weather activities is from early July to mid August, with a peak score in the last week of July.

Beach/Pool Score in Portland

Beach/Pool Score in Portlandbest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810104.74.70.00.0NowNowtemperaturetemperature cloudscloudsprecipitationprecipitationbeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

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.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Portland typically lasts for 5.7 months (173 days), from around April 24 to around October 14, rarely starting before April 7 or after May 10, and rarely ending before September 28 or after October 31.

Time Spent in Various Temperature Bands and the Growing Season in Portland

Time Spent in Various Temperature Bands and the Growing Season in Portlandgrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Apr 2450%Apr 2450%Oct 1450%Oct 1450%May 1090%May 1090%Sep 2890%Sep 2890%Apr 710%Apr 710%Oct 3110%Oct 3110%Jul 20100%Jul 20100%NowNowfrigidfreezingvery coldcoldcoolcomfortablewarm
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Portland should appear around May 10, only rarely appearing before April 29 or after May 19.

Growing Degree Days in Portland

Growing Degree Days in PortlandJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F500°F500°F1,000°F1,000°F1,500°F1,500°F2,000°F2,000°F2,500°F2,500°FMay 1090°FMay 1090°FJul 15900°FJul 15900°FSep 21,800°FSep 21,800°FDec 312,245°FDec 312,245°FNowNow
The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

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 7 to August 22, with an average daily incident shortwave energy per square meter above 5.7 kWh. The brightest month of the year in Portland is July, with an average of 6.5 kWh.

The darker period of the year lasts for 3.4 months, from October 31 to February 10, with an average daily incident shortwave energy per square meter below 2.5 kWh. The darkest month of the year in Portland is December, with an average of 1.5 kWh.

Average Daily Incident Shortwave Solar Energy in Portland

Average Daily Incident Shortwave Solar Energy in PortlandbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh0 kWh1 kWh1 kWh2 kWh2 kWh3 kWh3 kWh4 kWh4 kWh5 kWh5 kWh6 kWh6 kWh7 kWh7 kWh8 kWh8 kWh9 kWh9 kWhJun 306.8 kWhJun 306.8 kWhDec 231.5 kWhDec 231.5 kWhMay 75.7 kWhMay 75.7 kWhAug 225.7 kWhAug 225.7 kWhOct 312.5 kWhOct 312.5 kWhFeb 102.5 kWhFeb 102.5 kWhNowNow
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Solar Energy (kWh) 1.82.73.85.05.96.56.55.94.73.22.01.5

For the purposes of this report, the geographical coordinates of Portland are 43.661 deg latitude, -70.255 deg longitude, and 59 ft elevation.

The topography within 2 miles of Portland contains only modest variations in elevation, with a maximum elevation change of 161 feet and an average elevation above sea level of 23 feet. Within 10 miles contains only modest variations in elevation (492 feet). Within 50 miles contains significant variations in elevation (2,339 feet).

The area within 2 miles of Portland is covered by water (49%) and artificial surfaces (45%), within 10 miles by water (41%) and trees (29%), and within 50 miles by trees (48%) and water (45%).

This report illustrates the typical weather in 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Portland.

For each station, the records are corrected for the elevation difference between that station and 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 Portland is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Portland and a given station.

The stations contributing to this reconstruction are:

To get a sense of how much these sources agree with each other, you can view a comparison of Portland and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for airports and weather stations are provided by AskGeo.com .

Maps are © OpenStreetMap contributors.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.

Please review our full terms contained on our Terms of Service page.