This report describes the historical weather record at the O'Hare International Airport (Chicago, Illinois, United States) during 1951. This station has records back to December 1947.
Chicago, Illinois has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by built-up areas (37%), grasslands (36%), oceans and seas (22%), forests (3%), and croplands (3%)
Daylight saving time (DST) was observed at Chicago, Illinois during 1951. There were two time changes during 1951:
1951 was not a leap year, so it has 365 days and no February 29th. The first leap year before 1951 was 1948 and the first after was 1952.
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 1951 they occurred on:
|Spring Equinox||Wednesday, 21 March 1951.|
|Summer Solstice||Friday, 22 June 1951.|
|Fall Equinox||Sunday, 23 September 1951.|
|Winter Solstice||Saturday, 22 December 1951.|
The hottest day of 1951 was August 31, with a high temperature of 91°F. For reference, on that day the average high temperature is 80°F and the high temperature exceeds 89°F only one day in ten. The hottest month of 1951 was July with an average daily high temperature of 81°F.
Relative to the average, the hottest day was March 6. The high temperature that day was 65°F, compared to the average of 42°F, a difference of 23°F. In relative terms the warmest month was May, with an average high temperature of 71°F, compared to an typical value of 70°F.
The longest warm spell was from January 9 to January 21, constituting 13 consecutive days with warmer than average high temperatures. The month of January had the largest fraction of warmer than average days with 61% days with higher than average high temperatures.
The coldest day of 1951 was January 30, with a low temperature of -22°F. For reference, on that day the average low temperature is 17°F and the low temperature drops below -0°F only one day in ten. The coldest month of 1951 was January with an average daily low temperature of 14°F.
Relative to the average, the coldest day was January 30. The low temperature that day was -22°F, compared to the average of 17°F, a difference of 38°F. In relative terms the coldest month was November, with an average low temperature of 24°F, compared to an typical value of 33°F.
The longest cold spell was from July 4 to July 21, constituting 18 consecutive days with cooler than average low temperatures. The month of July 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 24 to February 5, constituting 13 consecutive days with temperatures strictly below freezing.
The clearest month of 1951 was August, with 45% of days being more clear than cloudy. The longest spell of clear weather was from September 13 to September 20, constituting 8 consecutive days that were clearer than they were cloudy.
The cloudiest month of 1951 was February, with 64% of days being more cloudy than clear. The longest spell of cloudy weather was from February 10 to February 22, constituting 13 consecutive days that were cloudier than they were clear.
This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.
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 1951 with the most precipitation observations was March 13. There were 24 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 March, with 163 hourly present weather reports involving some form of precipitation.
As determined by the present weather reports, the longest dry spell was from November 26 to December 6, constituting 11 consecutive days with no observed precipitation. The month with the largest fraction of days without observed precipitation was August, with 71% of days reporting no observed precipitation at all.
The month with the largest fraction of days with at least some observed precipitation was April, with 73% of days reporting some observed precipitation.
In this section we consider only those weather reports that indicate liquid precipitation. For the purposes of this analysis, we include thunderstorms even though some thunderstorms are not accompanied by liquid precipitation.
The month of 1951 with the largest number of those reports was April, with a total of 114 reports. The day with the largest number of those reports was May 10, with a total of 24 reports.
This station reports when snow is observed falling but does not report the quantity of snow that has fallen or the depth of snow on the ground.
In this section we consider hourly weather reports that contain an observation of falling snow. These reports do not necessarily correspond to accumulation.
The first reported snow fall in 1951 was on November 3; the last was on April 16. The month of 1951 with the largest number of those reports was December, with a total of 118 reports. The day with the largest number of those reports was March 13, with a total of 24 reports.
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 1951 was May with an average daily low humidity of 46%, and the most humid month was February 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 1951, January had 31 dry days, no comfortable days, and no humid days; April had 22 dry days, 4 comfortable days, and 4 humid days; July had no dry days, 14 comfortable days, and 17 humid days; and October had 14 dry days, 13 comfortable days, and 4 humid days.
The highest sustained wind speed was 52 mph, occurring on March 3; the highest daily mean wind speed was 30 mph (March 3);
The windiest month was March, with an average wind speed of 15 mph. The least windy month was August, with an average wind speed of 7 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 1951 with the lowest average visibility was December 20, with an average visibility of 0.9 mi. The month with the lowest average visibility was February, with an average visibility of 6.0 mi. With an average visibility of 10.9 mi, the month of September 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 1951 with the lowest average cloud ceiling was September 18, with an average cloud ceiling of 49'. The month with the lowest average cloud ceiling was February, with an average cloud ceiling of 5954'. The month of June has the highest average cloud ceiling, with an average cloud ceiling of 12560'.