August 14: ORD

Today is August 14th. It's the 227th day of the year. 139 days remain. It's week 33 of the year.
 
Unless noted, the following data is based upon observations collected by the National Weather Service, Chicago, at O'Hare International Airport (ORD) between November 1978 and last year. ORD has been the official site of record for Chicago since Thursday, January 17, 1980. Before this, the official site of record was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. Before that, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 82 and the normal low is 63. I've calculated the 33-year averages at 81 and 62.

On the hot side, in 1995 (O'Hare's warmest August 14th) the high was 95 (O'Hare's hottest high of the date and our most recent 90s high) with the record warmest low of 79. In 1988 the high was 92 with a low of 75 (O'Hare's co-second warmest low of the date).   The record high of 99 was set in 1944 at Midway. 28 of the past 33 highs (85%) were in the: 70s (14) and 80s (14). Four highs were in the hot 90s. One high was in the cool 60s (67 in 1992). In 1959 the low was a warm 75 degrees (O'Hare's other co-second warmest low). 

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1970 from the 11th through the 17th, highs were at least 85. The warmest was 88 on the 15th. Lows were at least 62 except for 57 on the 17th. In 1969 from the 12th through the 18th, highs were at least 85. The warmest was 88 on the 14th. Lows were at least 68 except for 61 on the 12th. The warmest low was 74 on the 14th. In 1967 the low was a cold 48 degrees which is equal to the day's record low. In 1964 the high was 76 with a cold low of 42, a 34 degree spread and a cool day. That low of 42 was colder than the record low. In 1963 the high was 72 with a cold low of 48, a cool day. That low of 48 was also equal to the day's record low. In 1962 the high was a cool 70 degrees. In 1959 the low was a warm 75 degrees.

More recently, there was a large spread of 33 degrees in 1984 (84/51).
 
On the cool side, in 2004 (O'Hare's co-second coolest August 14th) the high was 70 with a low of 50 (our most recent 50s low). In 1992 the high was 67 (our only 60s high) with a low of 56. In 1979 the high was 70 with a low of 53. The other cold low was 51 in 1984. The record low of 48 was set at Midway in 1964. The record coolest high of 65 occurred way back in 1885, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 50s (12) and 60s (18). Three lows were in the warm 70s.  O'Hare's coolest August 14th was in 1964 as the high was 76 with a low of 42 (a low colder than the official record low and O'Hare's coldest of the date). O'Hare's other co-second coolest August 14th was in 1963 as the high was 72 with a low of 48. 1967 also had a low of 48. These 48 degree lows are equal to the current official record low. 

As you can see, this is a day dominated by highs in the 70s or 80s and lows in the 50s or 60s. There's an ongoing long stretch of such highs. This is 16 years from 1996 through last year, 2011. There were two long stretches of such occurrences with the lows. The first was nine years from 1979 through 1987. The second was 14 years from 1996 through 2009.
  
The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:30 and sunrise is at 6:00. Sunset is at 19:55 and twilight ends at 20:25. There's a total of 13 hours, 55 minutes of daylight today and 14 hours, 55 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:31 and sunrise is at 6:01. The moon is waning crescent. Illumination was 12% at midnight, will be 9% at noon and 7% at midnight tonight. Moonrise was at 2:57 this morning. Moonset is at 17:51 this afternoon. Moonrise is at 3:58 tomorrow morning. Moonlight time is 14 hours, 54 minutes which is 16 minutes shorter than yesterday.

Summer began on June 4th and runs for 110 days through September 21st. High temperatures in this period are usually in the 70s and 80s. Highs in the 90s and 100s occur infrequently. Labor Day is in 20 days.