September 15: ORD

Today is September 15th. It's the 258th day of the year. 107 days remain. It's week 37 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 75 and the normal low is 54. I've calculated the 31-year averages at 72 and 54.

On the hot side, in 1994 the high was 91 with a low of 71. Three years earlier, in 1991, the high was 91 with a low of 68. In 2004 the high was 86 with a low of 68. In 1992 the high was 85 with a low of 68. Another warm low was 67 in 1998. The record high of 99 was set back in 1939. The record warmest low of 75 was set back in 1927. Over the last 31 years, 22 highs (71%) were: 60s (11) and 70s (11). Eight highs were in the warmer: 80s (6) and 90s (2). One high was 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 1969 the low was a warm 69. In 1966 the high was 65 with a cool low of 40, a cool day. In 1964 the high was a cool 62. In 1963 the high was 78 with a low of 46, a 32 degree spread. In 1961 the low was a cool 41. In 1959 the high was a cool 62.

More recently, there was a large spread of 31 degrees in 1985 (71/40). There were small spreads of four degrees in 1993 (55/51), five degrees in 1998 (72/67) and seven degrees in 1980 (64/57).

On the cool side, in 2007 the high was 61 with the record low of 39. The former record low of 40 occurred in 1985. In 1984 the high was 62 with a low of 41. Other cool highs are the co-record coolest high of 55 in 1993, 62 in 1983 and 62 in 2000. The other co-record coolest high of 55 occurred in 1916, a time when the official thermometer was located on the lakefront. Over the last 31 years, 17 lows were 50s. Seven lows were in the cooler: 30s (1) and 40s (6). Seven lows were in the warmer: 60s (6) and 70s (1).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:05 and sunrise is at 6:33. Sunset is at 19:03 and twilight ends at 19:31. There's a total of 12 hours, 30 minutes of daylight today and 13 hours, 26 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 6:06 and sunrise is at 6:34. The moon reaches first quarter this morning at 50 minutes past midnight. Illumination was 50% at midnight, will be 55% at noon and 60% at midnight tonight. Moonrise is at 14:50 this afternoon. Moonset is at 23:57 tonight and moonrise is at 15:34 tomorrow afternoon. Moonlight time is 9 hours, 7 minutes which is 6 minutes longer than yesterday.

Citizenship day is in two days. -Bernie-