This report describes the typical weather at the Portland International Airport (Portland, Oregon, United States) weather station over the course of an average July. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Portland, Oregon has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by forests (69%), croplands (15%), built-up areas (11%), and lakes and rivers (4%).
The month of July is characterized by rising daily high temperatures, with daily highs ranging from 76Â°F to 82Â°F over the course of the month, exceeding 93Â°F or dropping below 66Â°F only one day in ten.
Over the course of July, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 51 minutes, implying an average day-over-day decrease of 1.6 minutes.
The shortest day of the month is July 31 with 14:46 hours of daylight; the longest day is July 3 with 15:37 hours of daylight.
The earliest sunrise is at 5:26am on July 1; the latest sunset is at 9:03pm on July 3; the latest sunrise is at 5:54am on July 31; the earliest sunset is at 8:40pm on July 31.
Daylight savings time is observed in 2012 but it neither starts nor ends in July, so the entire month is in daylight time.
The median cloud cover ranges from 50% (partly cloudy) to 66% (partly cloudy). The trend is for the sky to be clearing rapidly with the median cloud cover decreasing by 16% from the start to the end of the month.
On July 31, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 61% of the time, and overcast or mostly cloudy 38% of the time.
On July 1, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 64% of the time, and clear or mostly clear 35% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around July 1, occurring in 31% of days. Precipitation is least likely around July 29, occurring in 21% of days.
Throughout July, the most common forms of precipitation are light rain, moderate rain, and thunderstorms.
Light rain is the most severe precipitation observed during 51% of those days with precipitation. It is most likely around July 1, when it is observed during 16% of all days.
Moderate rain is the most severe precipitation observed during 26% of those days with precipitation. It is most likely around July 1, when it is observed during 9% of all days.
Thunderstorms are the most severe precipitation observed during 12% of those days with precipitation. They are most likely around July 28, when it is observed during 3% of all days.
Either snow is exceptionally unlikely to fall at this location in July or this station does not reliably report precipitation types.
The relative humidity typically ranges from 40% (comfortable) to 85% (very humid) over the course of a typical July, rarely dropping below 26% (dry), or exceeding 94% (very humid).
The air is driest around July 30, at which time the relative humidity drops below 46% (comfortable) three days out of four; it is most humid around July 1, rising above 81% (humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a typical July, the dew point typically varies from 48Â°F (dry) to 58Â°F (comfortable) and is rarely below 42Â°F (dry) or above 63Â°F (mildy humid).
The time of the month between July 1 and July 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of July typical wind speeds vary from 0 mph to 14 mph (calm to moderate breeze), rarely exceeding 18 mph (fresh breeze).
The highest average wind speed of 8 mph (light breeze) occurs around July 15, at which time the average daily maximum wind speed is 14 mph (moderate breeze).
The lowest average wind speed of 7 mph (light breeze) occurs around July 1, at which time the average daily maximum wind speed is 13 mph (moderate breeze).