September 27: ORD

Today is September 27th. It's the 270th day of the year. 95 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 70 and the normal low is 49. I've calculated the 32-year averages at 71 and 50.

On the warm side, in 1986 the high was 86 with a low of 68. A year later, in 1987, the high was 89 with a low of 61. In 1998 the high was 86 with a low of 60. Other warm highs were 84 in 1990 and 83 in 1979. The record high of 91 and record warmest low of 71 were set on the same hot day in 1971. 28 of the past 32 highs (88%) were in the: 60s (12), 70s (8) and 80s (8). Four highs were in the cool 50s. For an ongoing 16 straight years, since 1995, highs were in the 60s, 70s and 80s. 14 of these 16 years (88%) featured highs of at least 65 degrees. The exceptions were 61 in 2003 and 62 in 2001.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1975 the high was 70 with a low of 40, a 30 degree spread. In 1973 the high was 80 with a warm low of 63, a warm day. In 1971 the high was 86 with a low of 69, a hot day. 1971 was also the year of the warm records. In 1967 the high was a cool 55 degrees. In 1964 the high was 61 with a cold low of 35, a cool day. In 1963 the high was a warm 85 with a low of 52, a 33 degree spread. In 1961 the high was 71 with a low of 40, a 31 degree spread.

More recently, there were large spreads of 37 degrees in 1990 (84/47), 31 degrees in 1985 (68/37), 31 degrees in 2004 (76/45) and 30 degrees in 1983 (79/49). There were small spreads of seven degrees in 1993 (53/46) and 1994 (58/51).

On the cool side, in 1984 the high was the near-record coolest high of 50 (the record is 49, set in 1942) with a low of 36. In 1991 the high was 58 with a low of 34 (our most recent 30s low). Other cool highs were 53 in 1993 and 58 in 1994 (our most recent 50s high). Other cool lows were 37 in both 1985 and 1989. The record low of 31 was set in 1942. 24 of the last 32 lows (75%) were in the: 40s (14) and 50s (10). For an ongoing 12 consecutive years, since 1999, lows were in the 40s & 50s. Four lows were in the cold 30s and four were in the warm 60s. Our most recent 60s low was 60 in 1998. A great battle between 30s & 60s lows began in 1984. In 1984 & 1985, the 30s won as 36 and 37 degrees. Then from 1986 through 1988, the 60s took over as 68, 61 and 60 degrees. Then in 1989, a low of 37 occurred. The 30s returned in 1991 as 34 degrees. But more recently, in 1998, a low of 60 occurred. The score is now tied at 4 a piece!

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:18 and sunrise is at 6:46. Sunset is at 18:42 and twilight ends at 19:10. There's a total of 11 hours, 56 minutes of daylight today and 12 hours, 52 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:19 and sunrise is at 6:47. The moon is new today at 6:09. Illumination was 0% at midnight, will be 0% at noon and 1% at midnight tonight. Moonrise is at 7:02 this morning. Moonset is at 18:30 this afternoon. Moonrise is at 8:21 tomorrow morning. Moonlight time is 11 hours, 28 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 13 days.