This report describes the historical weather record at the Clinton Municipal Airport (Clinton, Iowa, United States) during 2009. This station has records back to January 1988.
Clinton, Iowa has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by croplands (82%), forests (6%), grasslands (5%), lakes and rivers (4%), and built-up areas (3%)
Daylight saving time (DST) was observed at Clinton, Iowa during 2009. There were two time changes during 2009:
2009 was not a leap year, so it has 365 days and no February 29th. The first leap year before 2009 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 2009 they occurred on:
|Spring Equinox||Friday, 20 March 2009.|
|Summer Solstice||Sunday, 21 June 2009.|
|Fall Equinox||Tuesday, 22 September 2009.|
|Winter Solstice||Monday, 21 December 2009.|
The hottest day of 2009 was June 23, with a high temperature of 95°F. For reference, on that day the average high temperature is 82°F and the high temperature exceeds 90°F only one day in ten. The hottest month of 2009 was June with an average daily high temperature of 79°F.
Relative to the average, the hottest day was March 17. The high temperature that day was 75°F, compared to the average of 48°F, a difference of 27°F. In relative terms the warmest month was November, with an average high temperature of 53°F, compared to an typical value of 47°F.
The longest warm spell was from November 5 to November 15, constituting 11 consecutive days with warmer than average high temperatures. The month of November had the largest fraction of warmer than average days with 77% days with higher than average high temperatures.
The coldest day of 2009 was January 15, with a low temperature of -24°F. For reference, on that day the average low temperature is 13°F and the low temperature drops below -4°F only one day in ten. The coldest month of 2009 was January with an average daily low temperature of 4°F.
Relative to the average, the coldest day was January 15. The low temperature that day was -24°F, compared to the average of 13°F, a difference of 37°F. In relative terms the coldest month was January, with an average low temperature of 4°F, compared to an typical value of 14°F.
The longest cold spell was from January 10 to February 1, constituting 23 consecutive days with cooler than average low temperatures. The month of January had the largest fraction of cooler than average days with 87% days with lower than average low temperatures.
The longest freezing spell was from January 5 to January 22, constituting 18 consecutive days with temperatures strictly below freezing.
The clearest month of 2009 was August, with 71% of days being more clear than cloudy. The longest spell of clear weather was from November 1 to November 14, constituting 14 consecutive days that were clearer than they were cloudy.
The cloudiest month of 2009 was October, with 68% of days being more cloudy than clear. The longest spell of cloudy weather was from December 18 to December 29, constituting 12 consecutive days that were cloudier than they were clear.
This station reports both the quantity of liquid precipitation and categorical observations of precipitation (e.g., moderate rain, or heavy snow). Both are subject to erroneous reports, but the former is particularly prone to false reports, especially ones indicating an excessive quantity of precipitation. Please bear this in mind when reading the extrema reported in this section.
The day with the largest quantity of precipitation was October 22. That day saw 1.606" of liquid (or liquid equivalent) precipitation, compared to a median value of 0.141". The month with the most precipitation was October, with 5.756", compared to a median value of 2.118".
As determined by quantitative measurements, the longest dry spell was from January 1 to September 20, constituting 263 consecutive days with no measured precipitation. The months January, February, March, April, May, June, July, and August were completely without measured precipitation.
The month with the largest fraction of days with at least some measured precipitation was October, with 48% of days reporting some measured precipitation.
This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.
The day in 2009 with the most precipitation observations was August 26. There were 9 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was August, with 26 hourly present weather reports involving some form of precipitation.
As determined by the present weather reports, the longest dry spell was from January 1 to June 1, constituting 152 consecutive days with no observed precipitation. The months January, February, March, April, May, September, October, November, and December were completely without observed precipitation.
The month with the largest fraction of days with at least some observed precipitation was August, with 16% of days reporting some observed precipitation.
Either snow is exceptionally rare at this location or this station did not reliably report it during 2009.
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 2009 was April with an average daily low humidity of 42%, and the most humid month was December with an average daily low humidity of 68%.
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 2009, January had 31 dry days, no comfortable days, and no humid days; April had 21 dry days, 9 comfortable days, and no humid days; July had no dry days, 22 comfortable days, and 5 humid days; and October had 20 dry days, 11 comfortable days, and no humid days.
The highest sustained wind speed was 41 mph, occurring on March 10; the highest daily mean wind speed was 24 mph (March 11); and the highest wind gust speed was 56 mph (July 24).
The windiest month was April, with an average wind speed of 13 mph. The least windy month was September, with an average wind speed of 6 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 2009 with the lowest average visibility was November 23, with an average visibility of 2.5 mi. The month with the lowest average visibility was September, with an average visibility of 7.7 mi. With an average visibility of 9.5 mi, the month of June 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 2009 with the lowest average cloud ceiling was March 6, with an average cloud ceiling of 166'. The month with the lowest average cloud ceiling was December, with an average cloud ceiling of 3788'. The month of June has the highest average cloud ceiling, with an average cloud ceiling of 6431'.