This report describes the typical weather at the Helsinki-Malmi Airport (Helsinki, Finland) weather station over the course of an average August. It is based on the historical records from 1999 to 2012. Earlier records are either unavailable or unreliable.
Helsinki has a humid continental climate with warm summers and no dry season. The area within 25 mi of this station is covered by forests (53%), oceans and seas (38%), and croplands (7%).
The month of August is characterized by falling daily high temperatures, with daily highs decreasing from 72°F to 65°F over the course of the month, exceeding 79°F or dropping below 58°F only one day in ten.
Over the course of August, the length of the day is very rapidly decreasing. From the start to the end of the month, the length of the day decreases by 2:38 hours, implying an average day-over-day decrease of 5.1 minutes.
The shortest day of the month is August 31 with 14:13 hours of daylight; the longest day is August 1 with 16:51 hours of daylight.
The earliest sunrise is at 5:00am on August 1; the latest sunset is at 9:51pm on August 1; the latest sunrise is at 6:13am on August 31; the earliest sunset is at 8:26pm on August 31.
Daylight savings time is observed in 2012 but it neither starts nor ends in August, so the entire month is in daylight time.
The median cloud cover ranges from 71% (partly cloudy) to 78% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 6% from the start to the end of the month.
On August 16, a representative day, the sky is clear or mostly clear 15% of the time, partly cloudy 15% of the time, and mostly cloudy or overcast 40% of the time.
The average probability that some form of precipitation will be observed in a given day is 26%, with little variation over the course of the month.
Throughout August, the most common forms of precipitation are light rain and moderate rain.
Light rain is the most severe precipitation observed during 54% of those days with precipitation. It is most likely around August 13, when it is observed during 15% of all days.
Moderate rain is the most severe precipitation observed during 28% of those days with precipitation. It is most likely around August 28, when it is observed during 9% of all days.
Either snow is exceptionally unlikely to fall at this location in August or this station does not reliably report precipitation types.
The relative humidity typically ranges from 52% (mildly humid) to 98% (very humid) over the course of a typical August, rarely dropping below 38% (comfortable) and reaching as high as 100% (very humid).
The air is driest around August 1, at which time the relative humidity drops below 60% (mildly humid) three days out of four; it is most humid around August 28, rising above 97% (very 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 August, the dew point typically varies from 47°F (dry) to 60°F (comfortable) and is rarely below 41°F (dry) or above 65°F (mildy humid).
The time of the month between August 1 and August 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of August typical wind speeds vary from 0 mph to 12 mph (calm to gentle breeze), rarely exceeding 16 mph (moderate breeze).
The highest average wind speed of 6 mph (light breeze) occurs around August 1, at which time the average daily maximum wind speed is 12 mph (gentle breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around August 28, at which time the average daily maximum wind speed is 12 mph (gentle breeze).