October 13: ORD

Today is October 13th. It's the 287th day of the year. 79 days remain. It's week 41 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 64 and the normal low is 44. I've calculated the 33-year averages at 64 and 42.

On the warm side, in 2008 the high was 77 with a low of 61 (O'Hare's co-second warmest low of the date). In 1995 the high was 83 (O'Hare's second hottest high of the date) with a low of 52, a 31 degree spread. The following year of 1996 saw a high of 77 with a low of 56. In 2000 the high was 78 with a low of 54. The other warm highs were 81 degrees in 1962, 81 degrees in 1989 and 80 degrees in 1968. The other warm lows were 60 degrees in 1984 and 56 degrees in 1970. The record high of 88 degrees was set in 1975 at Midway. The record warmest low of 67 degrees occurred back in 1920, a time when the official readings were taken adjacent to Lake Michigan. 29 of the past 33 highs (88%) were in the: 50s (11), 60s (11) and 70s (7). Two highs were in the warm 80s and two highs were in the cool 40s. O'Hare's warmest October 13th was in 1975 as the high was 87 (O'Hare's hottest high of the date) with a low of 64 (O'Hare's warmest low of the date). O'Hare's second warmest October 13th was in 1960 as the high was 79 with a low of 61 (O'Hare's other co-second warmest low of the date). The other warm day was in 1968 as the high was 80 with a low of 59.  

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1977 the high was 61 with a cold low of 31, a 30 degree spread. In 1975 the high was 87 with a low of 64, a hot day. 1975 was the year of the record high of 88 at Midway. In 1970 the low was a warm 56 degrees. In 1968 the high was 80 with a low of 59, a warm day. In 1964 the high was 68 with a cold low of 30, a 38 degree spread. In 1963 the high was 72 with a cold low of 32, a 40 degree spread. In 1962 the high was a warm 81 with a low of 47, a 34 degree spread. In 1960 the high was 79 with a low of 61, a warm day. In 1959 the high was a cool 47 degrees with a low of 38, a cool day.

More recently, there were additional large spreads of 40 degrees in 1989 (81/41), 32 degrees in 1987 (65/33), 32 degrees in 2003 (73/41), 30 degrees in 1997 (74/44) and 30 degrees in 1980 (58/28). There were small spreads of six degrees in 1984 (66/60) and seven degrees in 1986 (47/40).

On the cool side, in 1988 (O'Hare's coolest October 13th) the high was 53 with the record low of 25. Three years ago, in 2009, the high was 47 (one of O'Hare's co-coolest highs of the date) with a low of 34. In 1993 the high was 53 with a low of 28 (O'Hare's co-second coldest low of the date). 2009 and 1993 are tied as O'Hare's second coolest October 13th days. In 2006 the high was 50 with a low of 32. In 2002 the high was 50 with a low of 33. The other co-second coldest low of 28 degrees occurred in 1980. The other cold lows were 30 degrees in 1964, 31 degrees in 1977 and 32 degrees in 1963. The other cool highs are 47 degrees in 1986 (one of O'Hare's co-coolest highs of the date) and 52 degrees in 1979. The record coolest high of 45 degrees occurred back in 1909, at a time when the official readings were taken adjacent to Lake Michigan. 28 of the last 33 lows (85%) were in the: 30s (8), 40s (14) and 50s (6). Three lows were in the cold 20s. All of the 20s lows occurred quite long ago, in 1980 (28), 1988 (25) and 1993 (28). Two lows were in the warm 60s. The other cool day was in 1959 as the high was 47 (one of O'Hare's co-coolest highs of the date) with a low of 38.

There's an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 2008 the high was 77 with a low of 61, overall 15 degrees ABOVE normal. Then in 2009 the high was 47 with a low of 34, overall 13.5 degrees BELOW normal. 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:36 and sunrise is at 7:04. Sunset is at 18:14 and twilight ends at 18:42. There's a total of 11 hours, 10 minutes of daylight today and 12 hours, 6 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:37 and sunrise is at 7:05. The moon is waning crescent and will be new in two days at 7:02. Illumination was 7% at midnight, will be 4% at noon and 2% at midnight tonight. Moonrise was at 4:53 this morning. Moonset is at 16:58 this afternoon. Moonrise is at 6:05 tomorrow morning. Moonlight time is 12 hours, 5 minutes which is 38 minutes shorter than yesterday.

Warm Fall began September 22nd and runs for 41 days through November 1st. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. United Nations Day is in 11 days. Standard Time doesn't return until November 4th.