October 4: ORD

Today is October 4th. It's the 278th day of the year. 88 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 65 and 45.

On the warm side, in 2005 (O'Hare's warmest October 4th) the high was 87 (with 1967, O'Hare's hottest high of the date) with the record warmest low of 71. The former record warmest low of 69 degrees occurred in 1922. Also, that low of 71 degrees tied October 1, 1971 as the warmest October low temperature ever. In 2007 the high was 82 (with 1976, O'Hare's second warmest high of the date) with a low of 51, a 31 degree spread. The record high of 90 degrees was set in 1951 at Midway. 17 of the past 33 highs (52%) were in the 60s. For seven consecutive years, from 1989 through 1995, highs were in the 60s. Three of the past four years (2008-2010) featured highs in the 60s. Eight highs (24%) were in the warm: 70s (6) and 80s (2). Eight highs (24%) were in the cool 50s. O'Hare's second warmest October 4th was in 1967 as the high was 87 (tied with 2005 as O'Hare's hottest high of the date) and low of 66 (O'Hare's second warmest low of the date). Tied with 2007 as O'Hare's second hottest high of the date is the high of 82 degrees in 1976.

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 82 degrees. In 1975 the high was 75 with a low of 44, a 31 degree spread. In 1969 the high was 80 with a low of 61, a warm day. In 1967 the high was 87 with a low of 66, a hot day. In 1965 the high was 57 with a cold low of 33, a cool day. In 1963 the high was 73 with a low of 41, a 32 degree spread. In 1959 the high was 60 with a low of 55, a five degree spread.

More recently, there were additional large spreads of 36 degrees in 1982 (77/41), 33 degrees in 1987 (69/36), 33 degrees last year, in 2011 (76/43), 32 degrees in 1984 (70/38) and 31 degrees in 1993 (65/34). There were no small spreads of up to seven degrees. 

On the cool side, in 1980 (O'Hare's coolest October 4th) the high was 51 (O'Hare's coolest high of the date) with the co-record low of 32. In 1988 (O'Hare's second coolest October 4th) the high was 52 (O'Hare's second coolest high of the date) with a low of 36. The other cold lows were the other co-record low of 32 degrees in 1989, 33 degrees in 1965 and a low of 34 degrees in 1993. The other cool high of 54 degrees occurred in 1999. 32 of the last 33 lows (97%) were in the: 30s (12), 40s (10) and 50s (10). One low was in the warm 70s (the record warmest low of 71 degrees set in 2005). There have been no lows in the 60s over the last 33 years. O'Hare's third coolest October 4th was in 1965 as the high was 57 with a low of 33 (O'Hare's second coldest low of the date).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:26 and sunrise is at 6:54. Sunset is at 18:29 and twilight ends at 18:57. There's a total of 11 hours, 35 minutes of daylight today and 12 hours, 31 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:27 and sunrise is at 6:55. The moon is waning gibbous. Illumination was 85% at midnight, will be 81% at noon and 78% at midnight tonight. Moonset is at 11:16 this morning. Moonrise is at 20:59 tonight. Moonset is at 12:08 tomorrow afternoon. Moonlight time is 14 hours, 17 minutes which is 14 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 four days. Standard Time doesn't return until November 4th.