October 2: ORD

Today is October 2nd. It's the 276th day of the year. 90 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 68 and the normal low is 47. I've calculated the 33-year averages at 68 and 46.

On the warm side, in 1991 the high was 80 with a low of 59. In 2005 the high was 84 with a low of 54, a 30 degree spread. The following year of 2006 saw a high of 77 with a low of 61 (with 1967, O'Hare's second warmest low of the date). In 1983 the high was 88 (O'Hare's hottest high of the date) with a low of 49, a 39 degree spread. In 2000 the high was 81 with a low of 56. The record high of 91 and record warmest low of 69 were established on the same hot day in 1971 at Midway. Over the past 33 years, the four categories of highs have been almost equal: 50s (9 for 27%), 60s (11 for 34%), 70s (7 for 21%) and 80s (6 for 18%). O'Hare's warmest October 2nd was in 1971 as the high was 89 (O'Hare's hottest high of the date) with a low of 69 (O'Hare's warmest low of the date). O'Hare's second warmest 10/2 was in 1967 as the high was 84 with a low of 61 (with 2006, O'Hare's second warmest low of the date). The other warm highs of October 2nd are 82 degrees in 1963, 81 degrees in 1982, 80 degrees in 1976 and 80 degrees in 2001. The other warm lows of the date are 60 degrees in 1962, 60 degrees in 1986, 60 degrees in 2002 and 59 degrees in 1969. 

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1976 the high was a warm 80 with a low of 49, a 31 degree spread. In 1974 the high was 50 with a low of 27, a cool day. That low of 27 was colder than the record low of 28 which was set this same year at Midway. In 1972 the high was 78 with a low of 46, a 32 degree spread. In 1971 the high was 89 with a low of 69, a hot day. 1971 was the year of the record high of 91 and record warmest low of 69, both set at Midway. In 1969 the low was a warm 59 degrees. In 1967 the high was 84 with a low of 61, a warm day. In 1966 the high was 69 with a cold low of 33, a 36 degree spread. In 1963 the high was a warm 82 degrees. In 1962 the low was a warm 60 degrees. In 1961 the high was 52 with a low of 30, a cool day.

More recently, there were additional large spreads of 37 degrees in 1997 (79/42), 34 degrees in 1990 (73/39), 32 degrees in 1982 (81/49), 32 degrees in 2001 (80/48), 31 degrees in 1984 (68/37) and 30 degrees in 1992 (78/48). There was a small spread of seven degrees in 1986 (67/60). 

On the cool side, in 2003 the high was 53 with a low of 31. In 1981 the high was 52 (with 1961, O'Hare's coolest high of the date) and low of 32. In 1993 the high was 55 with a low of 33. In 1999 the high was 55 with a low of 36. In 1987 the high was 58 with a low of 33. The record low of 28 degrees was set in 1974. The record coolest high of 48 degrees occurred way back in 1888, at a time when the official readings were taken adjacent to Lake Michigan. 23 of the last 33 lows (70%) were in the: 30s (9) and 40s (14). O'Hare recorded six consecutive 30s and 40s lows from 1980 through 1985. Ten lows (30%) were in the warm: 50s (7) and 60s (3). Our most recent 30s low was 37 degrees in 2004. O'Hare's coolest October 2nd was in 1974 as the high was 50 (O'Hare's coolest high of the date) with a low of 27 (O'Hare's coldest low of the date). O'Hare's second coolest 10/2 was in 1961 as the high was 52 (with 1981, O'Hare's second coolest high of the date) and low of 30 (O'Hare's second coldest low of the date). The other cold lows are 33 degrees in 1966 and 34 degrees in 1985. The other cool high is 56 degrees in 2009.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:24 and sunrise is at 6:52. Sunset is at 18:32 and twilight ends at 19:00. There's a total of 11 hours, 40 minutes of daylight today and 12 hours, 36 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:25 and sunrise is at 6:53. The moon is waning gibbous, having passed the full Harvest moon three nights ago at 22:19. Illumination was 96% at midnight, will be 94% at noon and 91% at midnight tonight. Moonset was at 9:23 this morning. Moonrise is at 19:41 tonight. Moonset is at 10:21 tomorrow morning. Moonlight time is 13 hours, 42 minutes which is 27 minutes longer 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. Columbus Day is in six days. Standard Time doesn't return until November 4th.