September 22: ORD

Today is September 22nd. It's the 266th day of the year. 100 days remain. It's week 38 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 72 and the normal low is 51. I've calculated the 33-year averages at 71 and 51.

On the warm side, in 1986 (O'Hare's warmest September 22nd) the high was 90 (O'Hare's hottest high of the date) with a low of 65. In 2005 (O'Hare's third warmest September 22nd) the high was 87 (with 1959, O'Hare's second hottest high of the date) with a low of 63. O'Hare's fourth hottest high of 84 degrees occurred in 1980. Another post-1978 warm low is 63 degrees two years ago in 2010. The record high of 92 was set in 1956 at Midway. The record warmest low of 73 occurred way back in 1895, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the past 33 highs (79%) were in the: 60s (12) and 70s (14). Five highs (15%) were in the warm: 80s (4) and 90s (1). Two highs (6%) were in the cool 50s. For two periods of eight consecutive years, 1987 through 1994 and 1996 through 2003, highs were in the 60s and 70s. O'Hare's second warmest 9/22 was in 1959 as the high was 87 (O'Hare's second hottest high of the date along with 2005) with a low of 65. Tied as O'Hare's fourth warmest 9/22 is 1961 (O'Hare's third hottest high of the date of 85 with a low of 63) and 1968 (high of 83 and low of 65). O'Hare's warmest lows of the date of 68 degrees occurred in 1959, 1968 and 1986. O'Hare's second warmest low of the date is 64 degrees in 1964. O'Hare's third warmest lows of the date are 63 degrees in 1961, 2005 and 2010.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1976 the high was 71 with a cold low of 34 degrees, a 37 degree spread. In 1974 the high was 53 with a low of 32, a cold day. That low of 32 is equal to the record low. 1974 was also the year of the record coolest high of 49 at Midway. In 1970 the high was 68 with a low of 61, a seven degree spread. In 1968 the high was 83 with a warm low of 65, a warm day. In 1964 the low was a warm 64 degrees. In 1961 the high was 85 with a low of 63, a hot day. In 1959 the high was a 87 with a low of 65, a hot day.

More recently, there were large spreads of 35 degrees in 1989 (78/43), 32 degrees in 2004 (82/50) and 31 degrees in 1999 (72/41). There were no small spreads of up to seven degrees. 

On the cool side, in 1995 (O'Hare's coolest September 22nd) the high was 52 (O'Hare's coolest high of the date) with the record low of 32 (along with 1974, O'Hare's coldest low of the date), our earliest fall freeze. In 1983 (O'Hare's second coolest September 22nd) the high was 54 (O'Hare's third coolest high of the date) with a low of 37 (O'Hare's third coldest low of the date). The record coolest high of 49 degrees was set in 1974 at Midway. 24 of the last 33 lows (73%) were in the: 40s (12) and 50s (12). O'Hare recorded consecutive 40s & 50s lows as follows: six from 1989 through 1994 and nine from 1996 through 2004. Our most recent 40s low was 45 degrees in 2002. Two lows (6%) were in the cold 30s. Seven lows (21%) were in the warm 60s. O'Hare's pre-1979 cold 9/22 was in 1974 as the high was 53 (O'Hare's second coolest high of the date) with a low of 32 (with 1995, O'Hare's coldest low of the date). O'Hare's second coldest low of the date is 34 degrees in 1976.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:13 and sunrise is at 6:41. Sunset is at 18:50 and twilight ends at 19:18. There's a total of 12 hours, 9 minutes of daylight today and 13 hours, 5 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:14 and sunrise is at 6:42. The moon reaches first quarter this afternoon at 14:41. Illumination was 44% at midnight, will be 49% at noon and 55% at midnight tonight. Moonrise is at 14:06 this afternoon. Moonset is at 23:48 tonight. Moonrise is at 14:55 tomorrow afternoon. Moonlight time is 9 hours, 42 minutes which is six minutes longer than yesterday.

Summer ended yesterday. Warm Fall begins today and runs for 41 days through November 1st. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the cooler 30s and 40s occur infrequently. The Autumnal Equinox is this morning at 9:49. Columbus Day is in 16 days. Standard Time doesn't return until November 4th.