This report describes the typical weather at the Portela Airport (Lisbon Airport) (Lisbon, Portugal) weather station over the course of an average April. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Lisbon has a mediterranean climate with dry hot summers and mild winters. The area within 25 mi of this station is covered by shrublands (35%), croplands (31%), oceans and seas (30%), and built-up areas (3%).
The month of April is characterized by gradually rising daily high temperatures, with daily highs around 67°F throughout the month, exceeding 77°F or dropping below 58°F only one day in ten.
Over the course of April, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 1:09 hours, implying an average day-over-day increase of 2.3 minutes.
The shortest day of the month is April 1 with 12:39 hours of daylight; the longest day is April 30 with 13:48 hours of daylight.
The earliest sunrise is at 6:40am on April 30; the latest sunset is at 8:28pm on April 30; the latest sunrise is at 7:21am on April 1; the earliest sunset is at 8:00pm on April 1.
Daylight savings time is observed in 2012 but it neither starts nor ends in April, so the entire month is in daylight time.
The median cloud cover is 50% (partly cloudy) and does not vary substantially over the course of the month.
On April 15, a representative day, the sky is clear or mostly clear 31% of the time, partly cloudy 23% of the time, and mostly cloudy or overcast 22% of the time.
The average probability that some form of precipitation will be observed in a given day is 42%, with little variation over the course of the month.
Throughout April, the most common forms of precipitation are moderate rain, light rain, thunderstorms, and drizzle.
Moderate rain is the most severe precipitation observed during 46% of those days with precipitation. It is most likely around April 2, when it is observed during 20% of all days.
Light rain is the most severe precipitation observed during 28% of those days with precipitation. It is most likely around April 14, when it is observed during 12% of all days.
Thunderstorms are the most severe precipitation observed during 12% of those days with precipitation. They are most likely around April 23, when it is observed during 5% of all days.
Drizzle is the most severe precipitation observed during 11% of those days with precipitation. It is most likely around April 1, when it is observed during 5% of all days.
Either snow is exceptionally unlikely to fall at this location in April or this station does not reliably report precipitation types.
The relative humidity typically ranges from 52% (mildly humid) to 93% (very humid) over the course of a typical April, rarely dropping below 32% (comfortable) and reaching as high as 100% (very humid).
The air is driest around April 28, at which time the relative humidity drops below 62% (mildly humid) three days out of four; it is most humid around April 8, 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 April, the dew point typically varies from 43°F (dry) to 54°F (very comfortable) and is rarely below 34°F (dry) or above 60°F (comfortable).
The time of the month between April 1 and April 30 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of April typical wind speeds vary from 3 mph to 17 mph (light air to moderate breeze), rarely exceeding 23 mph (fresh breeze).
The highest average wind speed of 10 mph (gentle breeze) occurs around April 2, at which time the average daily maximum wind speed is 16 mph (moderate breeze).
The lowest average wind speed of 9 mph (gentle breeze) occurs around April 28, at which time the average daily maximum wind speed is 16 mph (moderate breeze).