This report describes the historical weather record at the Mount Wilson (Pasadena, California, United States) during 2013. This station has records back to January 1949.
Pasadena, California has a mediterranean climate with dry hot summers and mild winters. The area within 25 mi of this station is covered by built-up areas (32%), shrublands (30%), forests (30%), and grasslands (7%)
Daylight saving time (DST) was observed at Pasadena, California during 2013. There were two time changes during 2013:
2013 was not a leap year, so it has 365 days and no February 29th. The first leap year before 2013 was 2012 and the first after was 2016.
The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2013 they occurred on:
|Spring Equinox||Wednesday, 20 March 2013.|
|Summer Solstice||Friday, 21 June 2013.|
|Fall Equinox||Sunday, 22 September 2013.|
|Winter Solstice||Saturday, 21 December 2013.|
The hottest day of 2013 was June 30, with a high temperature of 99°F. For reference, on that day the average high temperature is 80°F and the high temperature exceeds 86°F only one day in ten. The hottest month of 2013 was July with an average daily high temperature of 83°F.
Relative to the average, the hottest day was December 17. The high temperature that day was 75°F, compared to the average of 51°F, a difference of 24°F. In relative terms the warmest month was June, with an average high temperature of 80°F, compared to an typical value of 74°F.
The longest warm spell was from March 10 to March 31, constituting 22 consecutive days with warmer than average high temperatures. The month of March had the largest fraction of warmer than average days with 84% days with higher than average high temperatures.
The coldest day of 2013 was September 3, with a low temperature of -99°F. For reference, on that day the average low temperature is 62°F and the low temperature drops below 54°F only one day in ten. The coldest month of 2013 was November with an average daily low temperature of 14°F.
Relative to the average, the coldest day was September 3. The low temperature that day was -99°F, compared to the average of 62°F, a difference of 161°F. In relative terms the coldest month was November, with an average low temperature of 14°F, compared to an typical value of 38°F.
The longest cold spell was from July 28 to August 13, constituting 17 consecutive days with cooler than average low temperatures. The month of August had the largest fraction of cooler than average days with 58% days with lower than average low temperatures.
This station did not reliably report the cloud coverage during 2013.
Either snow is exceptionally rare at this location or this station did not reliably report it during 2013.
Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.
When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of 2013 was June with an average daily low humidity of 12%, and the most humid month was November with an average daily low humidity of 35%.
But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.
Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.
Generally speaking, dew points below 50°F will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 50°F to 68°F are fairly comfortable to most people, and dew points above 68°F are increasingly uncomfortable, becoming oppressive around 77°F.
To take some examples, and basing our categorization on the daily high dew point in 2013, January had no dry days, no comfortable days, and no humid days; April had 27 dry days, 3 comfortable days, and no humid days; July had 11 dry days, 20 comfortable days, and no humid days; and October had 29 dry days, 2 comfortable days, and no humid days.
The highest sustained wind speed was 39 mph, occurring on February 21; the highest daily mean wind speed was 12 mph (May 6); and the highest wind gust speed was 39 mph (February 21).
The windiest month was March, with an average wind speed of 5 mph. The least windy month was July, with an average wind speed of 0 mph.
This station did not reliably report the visibility during 2013.
This station did not reliably report the cloud ceiling during 2013.