This report describes the typical weather at the Comodoro Arturo Merino Benítez International Airport (Santiago, Chile) weather station over the course of an average December. It is based on the historical records from 1975 to 2012. Earlier records are either unavailable or unreliable.
Santiago has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by grasslands (44%), shrublands (25%), croplands (22%), and built-up areas (6%).
The month of December is characterized by gradually rising daily high temperatures, with daily highs increasing from 81°F to 84°F over the course of the month, exceeding 89°F or dropping below 73°F only one day in ten.
Over the course of December, the length of the day is essentially constant. The shortest day of the month is December 1 with 14:12 hours of daylight; the longest day is December 21 with 14:22 hours of daylight.
The earliest sunrise is at 6:26am on December 4; the latest sunset is at 8:56pm on December 31; the latest sunrise is at 6:37am on December 31; the earliest sunset is at 8:39pm on December 1.
Daylight saving time is observed in 2012 but it neither starts nor ends in December, so the entire month is in daylight time.
The median cloud cover ranges from 4% (clear) to 14% (mostly clear). The trend is for the sky to be clearing with the median cloud cover decreasing by 10% from the start to the end of the month.
On December 16, a representative day, the sky is clear or mostly clear 59% of the time, partly cloudy 9% of the time, and mostly cloudy or overcast 8% of the time.
The average probability that some form of precipitation will be observed in a given day is 4%, with little variation over the course of the month.
Throughout December, the most common forms of precipitation are drizzle, moderate rain, and light rain.
Drizzle is the most severe precipitation observed during 43% of those days with precipitation. It is most likely around December 1, when it is observed during 2% of all days.
Moderate rain is the most severe precipitation observed during 29% of those days with precipitation. It is most likely around December 1, when it is observed during 2% of all days.
Light rain is the most severe precipitation observed during 20% of those days with precipitation. It is most likely around December 1, when it is observed during 1% of all days.
Either snow is exceptionally unlikely to fall at this location in December or this station does not reliably report precipitation types.
The relative humidity typically ranges from 31% (comfortable) to 88% (very humid) over the course of a typical December, rarely dropping below 21% (dry) and reaching as high as 100% (very humid).
The air is driest around December 30, at which time the relative humidity drops below 36% (comfortable) three days out of four; it is most humid around December 1, rising above 82% (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 December, the dew point typically varies from 43°F (dry) to 54°F (very comfortable) and is rarely below 36°F (dry) or above 60°F (comfortable).
The time of the month between December 1 and December 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of December typical wind speeds vary from 0 mph to 18 mph (calm to fresh breeze), rarely exceeding 22 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around December 31, at which time the average daily maximum wind speed is 18 mph (fresh breeze).
The lowest average wind speed of 7 mph (light breeze) occurs around December 1, at which time the average daily maximum wind speed is 17 mph (moderate breeze).