October 1: ORD

Today is October 1st. It's the 275th day of the year. 91 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 48. I've calculated the 33-year averages at 70 and 47.

On the warm side, in 2002 (O'Hare's second warmest October 1st) the high was 82 (our most recent 80s high) with a low of 67 (O'Hare's second warmest low of the date). Two years prior, in 2000, the high was 83 with a low of 61.  The record high of 92 degrees and record warmest low of 71 degrees were established on the same hot day at Midway in 1971. 25 of the past 33 highs (76%) were in the: 60s (9) and 70s (16). For 14 consecutive years, from 1986 through 1999, highs were in the 60s and 70s. Four highs (12%) were in the warm 80s. Two of these happened between 1980 and 1983 and the other two occurred between 2000 and 2002. Four highs (12%) in the cool 50s. O'Hare's warmest October 1st was in 1971 as the high was 90 (O'Hare's warmest high of the date) with a low of 71 (O'Hare's warmest low of the date). O'Hare's second hottest high of the date is 85 degrees in 1969. The other warm highs of the date are 82 degrees in 1963, 82 degrees in 1976, 81 degrees in 1983, 80 degrees in 1968 and 80 degrees in 1980.  

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 60 with a low of 55, a five degree spread. In 1976 the high was a warm 82 with a low of 46, a 36 degree spread. In 1974 the high was 52 with a low of 33, a cool day. 1974 was also the year of the record low of 32, set at Midway. In 1973 the low was a warm 60 degrees. In 1971 the high was 90 with a low of 71, a hot day. 1971 was the year of the record high of 92 and record warmest low of 71, both set at Midway. In 1969 the high was a warm 85 with a low of 58, a warm day. In 1968 the high was 80 with a low of 61, a warm day. In 1967 the high was 77 with a low of 42, a 35 degree spread. In 1966 the low was a cold 34 degrees. In 1963 the high was a warm 82 with a low of 51, a 31 degree spread. In 1961 the high was 51 with a low of 34, a cool day. 1961 was also the year of the record coolest high of 49 degrees, set at Midway.

More recently, there were large spreads of 38 degrees in 1981 (76/38), 36 degrees in 1987 (73/37), 35 degrees in 1983 (81/46), 34 degrees in 1979 (77/43), 33 degrees in 1992 (74/41), 32 degrees in 1984 (65/33) and 30 degrees in 2006 (74/44). There was a small spread of four degrees in 1986 (61/57).

On the cool side, in 2003 (O'Hare's second coolest October 1st) the high was 53 (O'Hare's third coolest high of the date) with a low of 34. In 1985 the high was 55 with a low of 34. An interesting fact is that highs in the back-to-back-to back years of 1997, 1998 and 1999 were 60 degrees, some of the coolest highs of October 1st.  The record low of 32 degrees was set in 1974. The record coolest high of 49 degrees occurred in 1961. Both records were set at Midway. 26 of the last 33 lows (79%) were in the: 40s (17) and 50s (9). Five lows (15%) were in the cold 30s. Four of these five occurred between 1981 and 1987 with a lone one in 2003. We had a 15 year reprieve from lows in the 30s from 1988 through 2002, including 12 consecutive years (1988 through 1999) of lows in the 40s and 50s. The current eight year streak of lows in the 40s and 50s began in 2004. Two lows (6%) were in the warm 60s, just two years apart (2000 and 2002). O'Hare's co-coolest October 1st days were in: 1961 (high of 51 (O'Hare's coolest high of the date) and low of 34) and 1974 (high of 52 (O'Hare's second coolest high of the date) and low of 33 (with 1984, O'Hare's coldest lows of the date)). O'Hare's second coldest lows of the date were 34 degrees in 1961, 1966, 1985 and 2003. The other cool high of 56 degrees occurred last year, in 2011.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:23 and sunrise is at 6:51. Sunset is at 18:34 and twilight ends at 19:02. There's a total of 11 hours, 43 minutes of daylight today and 12 hours, 39 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:24 and sunrise is at 6:52. The moon is waning gibbous, having passed the full Harvest moon two nights ago at 22:19. Illumination was 99% at midnight, will be 97% at noon and 96% at midnight tonight. Moonset was at 8:23 this morning. Moonrise is at 19:08 tonight. Moonset is at 9:23 tomorrow morning. Moonlight time is 13 hours, 15 minutes which is 29 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 seven days. Standard Time doesn't return until November 4th.