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.

Daily High and Low Temperature in August

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The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Fraction of Time Spent in Various Temperature Bands in August

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The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

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.

Daily Hours of Daylight and Twilight in August

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The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

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.

Daily Sunrise & Sunset with Twilight and Daylight Savings Time in August

The solar day over the course of the year 2012 . From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (solar, civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight savings time are indicated by the "DST" labels.

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.

Median Cloud Cover in August

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The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

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.

Cloud Cover Types in August

The fraction of time spent in each of the five sky cover categories. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

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.

Probability of Precipitation at Some Point in the Day in August

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The fraction of days in which various types of precipitation are observed. If more than one type of precipitation is reported in a given day, the more severe precipitation is counted. For example, if light rain is observed in the same day as a thunderstorm, that day counts towards the thunderstorm totals. The order of severity is from the top down in this graph, with the most severe at the bottom.

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.

Types of Precipitation Throughout August

Relative frequency of various types of precipitation over the course of a typical August.

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.

Relative Humidity in August

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The average daily high (blue) and low (brown) relative humidity with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

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.

Dew Point in August

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The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

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).

Wind Speed in August

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The average daily minimum (red), maximum (green), and average (black) wind speed with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind Directions in August

The fraction of time spent with the wind blowing from the various directions over the entire year. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Fraction of Time Spent with Various Wind Directions in August

The fraction of time spent with the wind blowing from the various directions on a daily basis. Stacked values do not always sum to 100% because the wind direction is undefined when the wind speed is zero.