October 5: ORD

Today is October 5th. It's the 279th day of the year. 87 days remain. It's week 40 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 67 and the normal low is 46. I've calculated the 33-year averages at 66 and 44.

On the warm side, in 2005 (O'Hare's warmest October 5th) the high was 84 with the record warmest low of 69. The former record warmest low of 68 degrees occurred in 1922. In 2007 (O'Hare's second warmest October 5th) the high was 84 with a low of 62 (O'Hare's second warmest low of the date). In 1982 the high was 86 (with 1963, O'Hare's second hottest high of the date) with a low of 54, a 32 degree spread. In 1997 the high was the record high of 88 with a low of 52, a 36 degree spread. In 1990 the high was 85 (O'Hare's third hottest high of the date) with a low of 51, a 34 degree spread. 17 of the past 33 highs (52%) were in the 60s. Eight highs (24%) were in the warm: 70s (2) and 80s (6). The 70s highs occurred 14 years ago (71 in 1998) and 29 years ago (70 in 1983). Eight highs (24%) were in the cool 50s, most recently 57 degrees in 2003. O'Hare's other warm highs are 86 degrees in 1963 (with 1982, O'Hare's second hottest high of the date), 80 degrees last year (in 2011), 79 degrees in 1960, 79 degrees in 1970 and 79 degrees in 1971. O'Hare's other warm lows are 59 degrees in 1972, 58 degrees in 1959, 58 degrees in 1969 and 58 degrees in 1998.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1975 the high was 75 with a low of 42, a 33 degree spread. In 1972 the high was 64 with a warm low of 59, a five degree spread. In 1971 the high was a warm 79 degrees. In 1970 the high was also a warm 79 degrees. In 1969 the low was a warm 58 degrees. In 1968 the low was a cold 32 degrees. In 1966 the high was 61 with a cold low of 31, a 30 degree spread. In 1965 the high was 60 with a cold low of 30, a 30 degree spread. In 1963 the high was a hot 86 degrees with a low of 45, a 41 degree spread. A spread of 40 degrees or more is rare. In 1960 the high was a warm 79 degrees. In 1959 the low was a warm 58 degrees.

More recently, there were additional large spreads of 31 degrees last year, in 2011 (80/49), 30 degrees in 1993 (64/34) and 30 degrees in 1996 (69/39). There was a small spread of four degrees in 1995 (60/56). 

On the cool side, in 1980 (O'Hare's coolest October 5th) the high was 54 with the record low of 28. In 1988 (O'Hare's second coolest October 5th) the high was 54 with a low of 32. Those highs of 54 degrees are O'Hare's second coolest highs of the date. The record coolest high of 46 degrees occurred back in 1932 at the University of Chicago. 24 of the last 33 lows (73%) were in the: 30s (10) and 40s (14). O'Hare recorded six consecutive 30s and 40s lows from 1999 through 2004. One low (3%) was in the cold 20s. Eight lows (24%) were in the warm: 50s (6) and 60s (2). Our most recent 50s low was 58 degrees 14 years ago in 1998. O'Hare's other cold lows of the date are 30 degrees in 1965 (O'Hare's second coldest low), 31 degrees in 1966, 31 degrees in 2004, 32 degrees in 1968 and 34 degrees in 1993. O'Hare's coolest high of the date is 51 degrees in 2001. 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:27 and sunrise is at 6:55. Sunset is at 18:27 and twilight ends at 18:55. There's a total of 11 hours, 32 minutes of daylight today and 12 hours, 28 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:28 and sunrise is at 6:56. The moon is waning gibbous. Illumination was 78% at midnight, will be 74% at noon and 69% at midnight tonight. Moonset is at 12:08 this afternoon. Moonrise is at 21:45 tonight. Moonset is at 12:56 tomorrow afternoon. Moonlight time is 14 hours, 23 minutes which is six minutes longer than yesterday. Moonlight time is at its peak today.

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. Columbus Day is in three days. Standard Time doesn't return until November 4th.