September 21: ORD

Today is September 21st. It's the 264th day of the year. 101 days remain. It's week 38 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 72 and the normal low is 52. I've calculated the 31-year averages at 71 and 52.

On the hot side, in 2007 the high was 88 with a low of 64. In 1980 the high was 79 with a low of 69. Another hot high was 87 in 2005. The two warmest 80s highs occurred within the last five years. The record high of 92 was set at Midway in 1970. The record warmest low of 76 occurred in 1931, a time when the official readings were taken on the lakefront. Over the last 31 years, 14 highs were in the 60s. 15 highs have been in the warmer: 70s (7) and 80s (8). Two highs were in the cooler 50s.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1976 the low was a cool 40 degrees. In 1975 the high was a cool 58 with a low of 51, a seven degree spread. In 1971 the high was 72 with a low of 42, a 30 degree spread. In 1970 the high was 88 with a low of 68, a hot day and year of the record high. In 1965 the high was 80 with a warm low of 68, a warm day. In 1964 the high was 85 with a low of 65, a hot day. In 1962 the high was 71 with a cool low of 33, a 38 degree spread. That low of 33 was cooler than the record low. In 1959 the high was 84 with a low of 64, a warm day.

More recently, there were large spreads of 34 degrees in 2005 (87/53), 32 degrees in 1984 (80/48) and 31 degrees in 2004 (82/51). There was a small spread of seven degrees last year (67/60).

On the cool side, in 1995 the high was the record coolest high of 50 with a low of 41. In 1983 the high was 53, the only other 50s high, with the co-record low of 39. The other co-record low of 39 was set in 1991. These were the only 30s lows. 16 of the last 31 lows have been 50s. 11 lows were in the cooler: 30s (2) and 40s (9). Four lows were in the warmer 60s. Two of the last three years featured lows in the 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:12 and sunrise is at 6:40. Sunset is at 18:52 and twilight ends at 19:20. There's a total of 12 hours, 12 minutes of daylight today and 13 hours, 8 minutes between twilights. We are losing two to four minutes of daylight a day. Tomorrow twilight begins at 6:13 and sunrise is at 6:41. The moon is waxing gibbous. Illumination was 96% at midnight, will be 97% at noon and 99% at midnight tonight. Moonset is at 5:01 this morning. Moonrise is at 17:51 this afternoon. Moonset is at 6:01 tomorrow morning. Moonlight time is 11 hours, 10 minutes which is 37 minutes longer than yesterday.

Columbus Day is in 20 days. -Bernie-