This report describes the typical weather at the OR Tambo International Airport (Johannesburg, South Africa) weather station over the course of an average January. It is based on the historical records from 1994 to 2012. Earlier records are either unavailable or unreliable.
Johannesburg has a mild temperate climate with dry winters and warm summers. The area within 25 mi of this station is covered by grasslands (90%) and built-up areas (10%).
The month of January is characterized by essentially constant daily high temperatures, with daily highs around 76°F throughout the month, exceeding 82°F or dropping below 69°F only one day in ten.
Over the course of January, the length of the day is essentially constant. The shortest day of the month is January 31 with 13:19 hours of daylight; the longest day is January 3 with 13:44 hours of daylight.
The earliest sunrise is at 5:18am on January 1; the latest sunset is at 7:05pm on January 12; the latest sunrise is at 5:41am on January 31; the earliest sunset is at 7:00pm on January 31.
Daylight savings time (DST) is not observed in 2012.
The median cloud cover is 54% (partly cloudy) and does not vary substantially over the course of the month.
On January 16, a representative day, the sky is clear or mostly clear 33% of the time, partly cloudy 20% of the time, and mostly cloudy or overcast 31% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around January 3, occurring in 63% of days. Precipitation is least likely around January 31, occurring in 57% of days.
Throughout January, the most common forms of precipitation are thunderstorms, light rain, and moderate rain.
Thunderstorms are the most severe precipitation observed during 70% of those days with precipitation. They are most likely around January 3, when it is observed during 44% of all days.
Light rain is the most severe precipitation observed during 14% of those days with precipitation. It is most likely around January 1, when it is observed during 9% of all days.
Moderate rain is the most severe precipitation observed during 13% of those days with precipitation. It is most likely around January 31, when it is observed during 9% of all days.
Either snow is exceptionally unlikely to fall at this location in January or this station does not reliably report precipitation types.
The relative humidity typically ranges from 49% (comfortable) to 96% (very humid) over the course of a typical January, rarely dropping below 31% (comfortable) and reaching as high as 100% (very humid).
The air is driest around January 31, at which time the relative humidity drops below 57% (mildly humid) three days out of four; it is most humid around January 18, rising above 93% (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 January, the dew point typically varies from 51°F (very comfortable) to 61°F (comfortable) and is rarely below 44°F (dry) or above 65°F (mildy humid).
The time of the month between January 1 and January 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of January typical wind speeds vary from 2 mph to 15 mph (light air to moderate breeze), rarely exceeding 20 mph (fresh breeze).
The highest average wind speed of 9 mph (gentle breeze) occurs around January 1, at which time the average daily maximum wind speed is 15 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around January 29, at which time the average daily maximum wind speed is 13 mph (moderate breeze).