October 18: ORD

Today is October 18h. It's the 291st 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. Before that, 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 32-year averages at 61 and 41.

On the warm side, in 2007 the high was 78 (our most recent 70s high) with a low of 59. In 1979 the high was 74 with a low of 55. In 1994 the high was 68 with a low of 61 (our only 60s low), a seven degree spread. In 1985 the high was 68 with a low of 59. The record high of 87 was set in 1950 at Midway. The record warmest low of 65 occurred in 1910, a time when the official readings were taken adjacent to Lake Michigan. 24 of the past 32 highs (75%) were in the: 50s (11) and 60s (13). Six highs were in the warm 70s and two were in the cold 40s.

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 the high was 45 with a low of 25 (the only 20s low of the past 32 years and the third for October 18th in O'Hare's history). Three years earlier, in 1989, the high was 41 with a low of 32. Note that the only 40s highs of the past 32 years occurred close in years. The record low of 20 was set in 1948 at Midway. The record coolest high of 38 occurred way back in 1930, a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 32 lows (81%) were in the: 30s (15) and 40s (11). One low was in the cold 20s (25 in 1992). Five lows were in the warm: 50s (4) and 60s (1).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:41 and sunrise is at 7:09. Sunset is at 18:07 and twilight ends at 18:35. There's a total of 10 hours, 58 minutes of daylight today and 11 hours, 54 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:42 and sunrise is at 7:10. The moon is waning gibbous and reaches last quarter tomorrow night at 22:30. Illumination was 69% at midnight, will be 64% at noon and 59% at midnight tonight. Moonset is at 13:04 this afternoon. Moonrise is at 22:45 tonight. Moonset is at 13:44 tomorrow afternoon. Moonlight time is 14 hours, 19 minutes which is 15 minutes shorter than yesterday.

Warm Fall began September 22 and runs for 41 days through November 1. 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.