This report describes the typical weather at the Helsinki-Malmi Airport (Helsinki, Finland) weather station over the course of an average May. 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 May is characterized by rising daily high temperatures, with daily highs increasing from 56°F to 62°F over the course of the month, exceeding 71°F or dropping below 47°F only one day in ten.
Over the course of May, the length of the day is very rapidly increasing. From the start to the end of the month, the length of the day increases by 2:15 hours, implying an average day-over-day increase of 4.4 minutes.
The shortest day of the month is May 1 with 16:05 hours of daylight; the longest day is May 31 with 18:20 hours of daylight.
The earliest sunrise is at 4:09am on May 30; the latest sunset is at 10:29pm on May 31; the latest sunrise is at 5:16am on May 1; the earliest sunset is at 9:20pm on May 1.
Daylight savings time is observed in 2012 but it neither starts nor ends in May, so the entire month is in daylight time.
The median cloud cover is 85% (mostly cloudy) and does not vary substantially over the course of the month.
On May 16, a representative day, the sky is clear or mostly clear 6% of the time, partly cloudy 8% of the time, and mostly cloudy or overcast 33% of the time.
The average probability that some form of precipitation will be observed in a given day is 21%, with little variation over the course of the month.
Throughout May, the most common forms of precipitation are light rain and moderate rain.
Light rain is the most severe precipitation observed during 59% of those days with precipitation. It is most likely around May 22, when it is observed during 13% of all days.
Moderate rain is the most severe precipitation observed during 28% of those days with precipitation. It is most likely around May 28, when it is observed during 7% of all days.
Either snow is exceptionally unlikely to fall at this location in May or this station does not reliably report precipitation types.
The relative humidity typically ranges from 40% (comfortable) to 93% (very humid) over the course of a typical May, rarely dropping below 27% (dry) and reaching as high as 99% (very humid).
The air is driest around May 5, at which time the relative humidity drops below 47% (comfortable) three days out of four; it is most humid around May 26, rising above 89% (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 May, the dew point typically varies from 28°F (dry) to 48°F (dry) and is rarely below 20°F (dry) or above 54°F (very comfortable).
Over the course of May typical wind speeds vary from 0 mph to 13 mph (calm to moderate breeze), rarely exceeding 18 mph (fresh breeze).
The highest average wind speed of 7 mph (light breeze) occurs around May 20, at which time the average daily maximum wind speed is 13 mph (moderate breeze).
The lowest average wind speed of 7 mph (light breeze) occurs around May 1, at which time the average daily maximum wind speed is 13 mph (moderate breeze).