October 18: ORD

Today is October 18th. It's the 292nd day of the year. 74 days remain. It's week 42 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 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 62 and the normal low is 42. I've calculated the 33-year averages at 61 and 41.

On the warm side, in 2007 (O'Hare's warmest October 18th) the high was 78 (O'Hare's second warmest high of the date) with a low of 59 (with 1985, O'Hare's second warmest low of the date). In 1979 the high was 74 with a low of 55. In 1994 the high was 68 with a low of 61 (O'Hare's warmest low of the date), a seven degree spread. In 1985 the high was 68 with a low of 59 (with 2007, O'Hare's second warmest low of the date). The record high of 87 degrees was set in 1950 at Midway. The record warmest low of 65 degrees occurred in 1910, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 50s (12) and 60s (13). O'Hare recorded consecutive 50s and 60s highs as follows: six from 1983 through 1988 and seven from 1993 through 1999. Six highs (18%) were in the warm 70s. Two highs (6%) were in the cold 40s. The 40s highs were fairly close in years (41 degrees in 1989 and 45 degrees in 1992). O'Hare's second warmest October 18th was in 1965 as the high was 80 (O'Hare's warmest high of the date) with a low of 55. O'Hare's third warmest October 18th was in 1971 as the high was 77 (O'Hare's third warmest high of the date) and low of 56. Another warm day was 1963 as the high was 71 with a low of 58. 

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 52 with a cold low of 28, a cool day. In 1975 the high was 52 with a low of 46, a six degree spread. In 1974 the high was a cold 47 degrees. In 1972 the high was 38 with a low of 29, a cold day. In 1971 the high was 77 with a low of 56, a warm day. In 1966 the high was a cool 50 with a low of 44, a six degree spread. In 1965 the high was 80 (O'Hare's only 80s high) with a low of 55, a warm day. In 1963 the high was 71 with a warm low of 58, a warm day.

More recently, there were large spreads of 32 degrees in 2000 (70/38) and 30 degrees in 2005 (73/43). There were no additional small spreads of up to seven degrees.

On the cold side, in 1992 (O'Hare's second coolest October 18th) the high was 45 with a low of 25 (O'Hare's coldest low of the date). Three years earlier, in 1989 (O'Hare's third coolest October 18th), the high was 41 (O'Hare's second coolest high of the date) with a low of 32. The record low of 20 degrees was set in 1948 at Midway. The record coolest high of 38 degrees occurred way back in 1930 at the University of Chicago. 27 of the last 33 lows (82%) were in the: 30s (15) and 40s (12). One low was in the cold 20s (25 degrees in 1992). Five lows were in the warm: 50s (4) and 60s (1). O'Hare's coolest October 18th was in 1972 as the high was 38 (O'Hare's coolest and only 30s high of the date) and low of 29 (O'Hare's third coldest low of the date). Another cool day was in 1976 as the high was 52 with a low of 28 (O'Hare's second coldest low of the date). O'Hare also had cool highs of 47 degrees in 1974 and 50 degrees in 1966.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:42 and sunrise is at 7:10. Sunset is at 18:06 and twilight ends at 18:34. There's a total of 10 hours, 56 minutes of daylight today and 11 hours, 52 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:43 and sunrise is at 7:11. The moon is waxing crescent. Illumination was 11% at midnight, will be 15% at noon and 19% at midnight tonight. Moonrise is at 10:57 this morning. Moonset is at 20:37 tonight. Moonrise is at 11:59 tomorrow morning. Moonlight time is 9 hours, 40 minutes which is 13 minutes shorter than yesterday. Moonlight time is at its least today and tomorrow. 

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 six days. Standard Time doesn't return until November 4th.