This report describes the historical weather record at the Chester County G O Carlson Airport (Coatesville, Pennsylvania, United States) during 2011. This station has records back to November 2007.
Coatesville, Pennsylvania has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by forests (61%), croplands (32%), and built-up areas (5%)
Daylight saving time (DST) was observed at Coatesville, Pennsylvania during 2011. There were two time changes during 2011:
2011 was not a leap year, so it has 365 days and no February 29th. The first leap year before 2011 was 2008 and the first after is 2012.
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 2011 they occurred on:
|Spring Equinox||Sunday, 20 March 2011.|
|Summer Solstice||Tuesday, 21 June 2011.|
|Fall Equinox||Friday, 23 September 2011.|
|Winter Solstice||Thursday, 22 December 2011.|
The hottest day of 2011 was July 22, with a high temperature of 100°F. For reference, on that day the average high temperature is 84°F and the high temperature exceeds 89°F only one day in ten. The hottest month of 2011 was July with an average daily high temperature of 89°F.
Relative to the average, the hottest day was February 18. The high temperature that day was 68°F, compared to the average of 40°F, a difference of 28°F. In relative terms the warmest month was December, with an average high temperature of 48°F, compared to an typical value of 41°F.
The longest warm spell was from May 23 to June 3, constituting 12 consecutive days with warmer than average high temperatures. The month of December had the largest fraction of warmer than average days with 81% days with higher than average high temperatures.
The coldest day of 2011 was January 24, with a low temperature of 5°F. For reference, on that day the average low temperature is 24°F and the low temperature drops below 16°F only one day in ten. The coldest month of 2011 was January with an average daily low temperature of 22°F.
Relative to the average, the coldest day was January 24. The low temperature that day was 5°F, compared to the average of 24°F, a difference of 19°F. In relative terms the coldest month was January, with an average low temperature of 22°F, compared to an typical value of 25°F.
The longest cold spell was from January 5 to January 19, constituting 15 consecutive days with cooler than average low temperatures. The month of January had the largest fraction of cooler than average days with 74% days with lower than average low temperatures.
The longest freezing spell was from January 7 to January 15, constituting 9 consecutive days with temperatures strictly below freezing.
The clearest month of 2011 was July, with 94% of days being more clear than cloudy. The longest spell of clear weather was from July 9 to August 3, constituting 26 consecutive days that were clearer than they were cloudy.
The cloudiest month of 2011 was September, with 40% of days being more cloudy than clear. The longest spell of cloudy weather was from May 13 to May 21, constituting 9 consecutive days that were cloudier than they were clear.
This station reports the quantity of liquid precipitation but not observations of weather events in the area. For this reason, this section will only discuss the quantity of precipitation and not its type.
The day with the largest quantity of precipitation was January 26. That day saw 24.965" of liquid (or liquid equivalent) precipitation, compared to a median value of 0.307". The month with the most precipitation was January, with 46.406", compared to a median value of 10.181".
As determined by quantitative measurements, the longest dry spell was from February 6 to February 21, constituting 16 consecutive days with no measured precipitation. The month with the largest fraction of dry days was July, with 77% of days reporting no measured precipitation at all.
The month with the largest fraction of days with at least some measured precipitation was April, with 50% of days reporting some measured precipitation.
Either snow is exceptionally rare at this location or this station did not reliably report it during 2011.
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 2011 was February with an average daily low humidity of 46%, and the most humid month was September with an average daily low humidity of 70%.
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 2011, January had 29 dry days, 2 comfortable days, and no humid days; April had 14 dry days, 11 comfortable days, and 5 humid days; July had no dry days, 4 comfortable days, and 24 humid days; and October had 15 dry days, 14 comfortable days, and 2 humid days.
The highest sustained wind speed was 40 mph, occurring on February 19; the highest daily mean wind speed was 27 mph (February 19); and the highest wind gust speed was 49 mph (February 19).
The windiest month was February, with an average wind speed of 9 mph. The least windy month was September, with an average wind speed of 4 mph.
Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.
The day of 2011 with the lowest average visibility was October 13, with an average visibility of 1.6 mi. The month with the lowest average visibility was September, with an average visibility of 7.2 mi. With an average visibility of 8.9 mi, the month of December had the highest average visibility.
The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.
The day of 2011 with the lowest average cloud ceiling was June 6, with an average cloud ceiling of 49'. The month with the lowest average cloud ceiling was November, with an average cloud ceiling of 1818'. The month of February has the highest average cloud ceiling, with an average cloud ceiling of 4617'.