September 26: ORD

Today is September 26th. It's the 269th day of the year. 96 days remain. It's week 39 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.

According to the National Climatic Data Center (NCDC), the normal high is 71 and the normal low is 50. I've calculated the 32-year averages at 70 and 50.

On the warm side, in 1998 the high was the record high of 90 (our only 90s high & last of the year) with a low of 68. In 1986 the high was 78 with a low of 69. Those 60s lows were our only ones. In 1999 the high was 86 with a low of 57. Other warm highs were 85 in 1987 and 83 in 1979. The record warmest low of 71 occurred in 1973. 24 of the last 32 highs (75%) were in the: 60s (15) and 70s (9). For an ongoing 11 straight years, from 2000 through last year (2010), highs were in the 60s & 70s. Since the high was just 60 last year, this ended 15 straight years of highs of at least 65 degrees from 1995 through 2009. Four highs were in the warm: 80s (3) and 90s (1). Four highs were in the cool 50s.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1978 the high was 76 with a low of 46, a 30 degree spread. In 1974 the high was 82 with a low of 50, a 32 degree spread. In 1973 the high was 82 with a warm low of 71, a warm day and year of the record warmest low of 71 at Midway. In 1966 the low was a cold 36. In 1965 the high was a cool 53 with a low of 42, a cool day. In 1963 the high was a warm 83 with a low of 50, a 33 degree spread.

More recently, there were large spreads of 39 degrees in 1987 (85/46), 32 degrees in 1979 (83/51) and 31 degrees in 1995 (76/45). There was a small spread of seven degrees in 1994 (58/51).

On the cool side, in 1984 the high was 53 with the near-record low of 36 (the record low of 35 was set in 1928). In 1991 the high was 60 with a low of 40. In 1980 the high was 58 with a low of 42. The other cool highs were 58 degrees in 1989 and 1994. The record coolest high of 47 occurred in 1942. 29 of the last 32 lows (91%) were in the: 40s (12) and 50s (17). There were two long consecutive stretches of lows in the 40s & 50s. The first was 11 years from 1987 through 1997. The second is an ongoing, 12 year stretch from 1999 through last year, 2010. One low was in the cold 30s and two were in the warm 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:17 and sunrise is at 6:45. Sunset is at 18:44 and twilight ends at 19:12. There's a total of 11 hours, 59 minutes of daylight today and 12 hours, 55 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:18 and sunrise is at 6:46. The moon is waning crescent. Illumination was 2% at midnight, will be 1% at noon and 0% at midnight tonight. Moonrise is at 5:45 this morning. Moonset is at 17:58 this afternoon. Moonrise is at 7:02 tomorrow morning. Moonlight time is 12 hours, 13 minutes which is 45 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. Columbus Day is in 14 days.