September 11: ORD

Today is September 11th. It's the 254th day of the year. 111 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 56. I've calculated the 31-year averages at 78 and 56.

On the hot side, in 2005 the high was 90 with a low of 69. Other warm highs were 88 in 1982, 87 in 1979, 87 in 1988, 87 in 1994 and 87 in 2000. The record high of 95 was set in 1952. The record warmest low of 73 occurred in 1961. Over the last 31 years, 26 highs (84% or 21 of 25) were: 70s (13) and 80s (13). One high was in the warmer 90s and four highs were in the cooler 60s. We get a high of 87 (12 degrees above normal) or higher every 5.2 years on average. The last one was that 90 in 2005.

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 90 with a low of 66, a hot day. In 1976 the high was 84 with a low of 53, a 31 degree spread. In 1974 the high was 87 with a low of 69, a hot day. In 1967 the high was 71 with a low of 41, a 30 degree spread. That low of 41 was cooler than the record low. In 1966 the high was 86 with a low of 49, a 37 degree spread. In 1962 the high was 80 with a low of 47, a 33 degree spread. In 1961 the high was 89 with a low of 68, a hot day and year of the record warmest low.

More recently, there were large spreads of 35 degrees in 1999 (81/46) and 30 degrees in 1988 (87/57). There was a small spread of seven degrees in 1991 (71/64).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. The coolest lows were the five in the 40s. The coolest of these was the record low of 42, set in 1993. The coolest highs were the four in the 60s. The coolest were 67 in both 1985 and 2006. The record coolest high of 61 occurred in 1940, a time when the official readings were taken on the lakefront. Over the last 31 years, 26 lows (84% or 21 of 25) were: 50s (15) and 60s (11). Five lows were in the cooler 40s. No lows were in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:01 and sunrise is at 6:29. Sunset is at 19:10 and twilight ends at 19:38. There's a total of 12 hours, 41 minutes of daylight today and 13 hours, 37 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 6:02 and sunrise is at 6:30. The moon is waxing crescent. Illumination was 12% at midnight, will be 16% at noon and 20% at midnight tonight. Moonrise is at 10:36 this morning. Moonset is at 20:40 tonight and moonrise is at 11:50 tomorrow morning. Moonlight time is 10 hours, 4 minutes which is 41 minutes shorter than yesterday.

Patriot Day is today and Grandparent's Day is tomorrow. -Bernie-