September 14: ORD

Today is September 14th. It's the 258th day of the year. 108 days remain. It's week 37 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 this, 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 76 and the normal low is 55. I've calculated the 33-year averages at 74 and 55.

On the hot side, in 1994 (O'Hare's warmest September 14th) the high was 90  with a low of 73 (O'Hare's warmest low of the date). Three years earlier, in 1991 (O'Hare's second warmest September 14th), the high was 90 with a low of 67. Those highs of 90 degrees, along with a high of 90 degrees in 1971, are O'Hare's hottest highs of the date. O'Hare's co-second warmest low of the date is 68 degrees in 1998. The record high of 99 and record warmest low of 76 were set on the same hot day back in 1939 at the University of Chicago. 25 of the past 33 highs (76%) were in the: 60s (9) and 70s (16). O'Hare recorded consecutive highs in the 60s and 70s as follows: 11 from 1977 through 1987 and seven from 1995 through 2001. Seven highs (21%) were in the hot: 80s (5) and 90s (2). One high (3%) was in the cool 50s (58 degrees last year in 2011). O'Hare's other co-second warmest low of 68 degrees occurred in 1969.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1975 the low was a cold 41 degrees. In 1974 the low was a cold 40 degrees, equal to the record low. In 1971 the high was a hot 90 with a low of 58, a 32 degree spread. In 1970 the high was a cool 59 with a low of 55, a four degree spread. In 1969 the low was a warm 68 degrees. In 1964 the high was 80 with a cold low of 42, a 38 degree spread. In 1963 the high was 70 with a cold low of 38, a 32 degree spread. That low of 38 was colder than the record low. In 1961 the high was a cool 63 degrees.

More recently, there were large spreads of 31 degrees in 1988 (81/50), 30 degrees in 1987 (76/46) and 30 degrees in 2002 (83/53). There was a small spread of seven degrees in 1998 (75/68). In 2008 we received more rain from the remnants of Hurricane Ike. O'Hare recorded 1.44 inches. Cincinnati had a peak wind gust of 74 miles an hour, causing power outages. 

On the cool side, last year, in 2011 (O'Hare's coolest September 14th) the high was 58 (O'Hare's coolest high of the date) with a low of 47. In 1996 (O'Hare's second coolest September 14th) the high was 60 (O'Hare's third coolest high of the date) with a low of 46. In 1985 the high was 69 with the record low of 40. The other cool high of 63 degrees occurred in 2001. The record coolest high of 54 degrees occurred way back in 1923, at a time when the official readings were taken adjacent to Lake Michigan. 18 of the last 33 lows (55%) were in the 50s. Nine lows (27%) were in the cold 40s. Six lows (18%) were in the warm: 60s (5) and 70s (1). Our most recent 60s low was 64 degrees in 2004. O'Hare's pre-1979 cold lows are 38 degrees in 1963 (O'Hare's coldest low of the date and a low colder than the record low), 40 degrees in 1974 (a low equal to the record low), 41 degrees in 1975 and 42 degrees in 1964. O'Hare's second coolest high of the date is 59 degrees in 1970.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:05 and sunrise is at 6:33. Sunset is at 19:04 and twilight ends at 19:32. There's a total of 12 hours, 31 minutes of daylight today and 13 hours, 27 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:06 and sunrise is at 6:34. The moon is waning crescent, heading towards new tomorrow at 21:11. Illumination was 4% at midnight, will be 2% at noon and 1% at midnight tonight. Moonrise was at 4:57 this morning. Moonset is at 18:00 tonight. Moonrise is at 6:06 tomorrow morning. Moonlight time is 13 hours, 3 minutes which is 36 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 60s, 90s and 100s occur infrequently. Citizenship Day is in three days.