October 21: ORD

Today is October 21st. It's the 294th day of the year. 71 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 60 and the normal low is 41. I've calculated the 32-year averages at 60 and 43.

On the warm side, in 1979 the high was 84 with a low of 70, the only 70s low for October 21st at O'Hare ever. The record warmest low of 70 was set in 1979 at Midway. In 2007 the high was 80 with a low of 60, the only 60s low of the past 32 years. In 1986 the high was 77 with a low of 52. The other warm high was 72 in 1994, our most recent 70s high. The only other 80s high at O'Hare was 80 in 1978. The record high of 87 was set in 1953 at Midway. 25 of the past 32 highs (78%) were in the: 50s (15) and 60s (10). There were three long periods of 50s & 60s highs. The first was six years from 1980 through 1985. The second was six years from 1988 through 1993. The third was nine years from 1998 through 2006. Four highs were in the warm: 70s (2) and 80s (2). Three highs were in the cold 40s. There were also three cold 40s highs between 1960 and 1976.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1978 the high was 80 with a low of 53, a warm day. In 1977 the high was a warm 74 degrees. In 1976 the high was a cold 46 with a low of 30, a cold day. In 1975 the high was a warm 73 degrees. In 1974 the low was a cold 27 degrees. In 1973 the high was 67 with a low of 37, a 30 degree spread. In 1971 the high was 73 with a low of 66, a seven degree spread and warm day. In 1968 the high was 69 with a low of 38, a 31 degree spread. In 1963 the high was 69 with a warm low of 59, a warm day. In 1961 the high was 49 with a low of 44, a five degree spread. In 1960 the high was 49 with a cold low of 27, a cold day.

More recently, there were large spreads of 32 degrees in 1991 (67/35), 32 degrees in 1999 (68/36) and 31 degrees in 1994 (72/41). There was a small spread of five degrees in 1983 (56/51).

On the cold side, in 1987 the high was 42 with a low of 32. In 1995 the high was 43 with a low of 36, a seven degree spread. In 1982 the high was 52 with a low of 27. The only other 20s lows were 27 degrees (in 1960 & 1974). The record low of 26 was set in 1952 at Midway. The record coolest high of 39 occurred back in 1913, a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 32 lows (78%) were in the: 30s (14) and 40s (11). There were 14 straight 30s & 40s lows from 1987 through 2000. One low was in the cold 20s, a total of just three in O'Hare's history for the date. Six lows were in the warm: 50s (4), 60s (1) and 70s (1). The only other 60s low is 66 in 1971, a total of just three 60s or 70s lows for the date, a rare occurrence.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:44 and sunrise is at 7:13. Sunset is at 18:03 and twilight ends at 18:31. There's a total of 10 hours, 50 minutes of daylight today and 11 hours, 47 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:45 and sunrise is at 7:14. The moon is waning crescent and reached last quarter two nights ago at 22:30. Illumination was 38% at midnight, will be 33% at noon and 28% at midnight tonight. Moonrise is at 0:56 this morning. Moonset is at 14:52 this afternoon. Moonrise is at 2:06 tomorrow morning. Moonlight time is 13 hours, 56 minutes which is 24 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 three days.