September 12: ORD

Today is September 12th. It's the 255th day of the year. 110 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 55. I've calculated the 31-year averages at 78 and 57.

On the hot side, in 2005 the high was 90 with a low of 68. Other warm highs were 88 in 1998, 87 in 1979 and 87 in 1994. The record high of 96 was set in 1952. The record warmest low of 72 occurred back in 1931, a time when the official readings were taken on the lakefront. 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.

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 61 with a low of 43, a cool day. That low of 43 is cooler than the record low. In 1973 the high was 76 with a low of 46, a 30 degree spread. In 1972 the high was 70 with a low of 64, a six degree spread. In 1967 the high was 79 with a low of 41, a 38 degree spread. That low of 41 is cooler than the record low. In 1966 the high was 84 with a low of 52, a 32 degree spread. In 1964 the high was 65 with a low of 38, a cool day. That low of 38 is cooler than the record low. In 1962 the high was a hot 91 with a low of 62, a hot day. In 1961 the low was a warm 68. In 1960 the high was a cool 62.

More recently, there were no large spreads of at least 30 degrees or more. There was a small spread of four degrees two years ago (73/69).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. The coolest days were 1985 (66/46) and three years ago (67/46). Both days featured our coolest lows of 46 degrees. The record low of 44 was set in 1955. The coolest highs were the four in the 60s. The coolest was the 66 in 1985. The others were 67 degrees (1989, 1996 and three years ago). The record coolest high of 53 occurred in 1902, 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 (13) and 60s (13). 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 6:02 and sunrise is at 6:30. Sunset is at 19:08 and twilight ends at 19:36. There's a total of 12 hours, 38 minutes of daylight today and 13 hours, 34 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 6:03 and sunrise is at 6:31. The moon is waxing crescent. Illumination was 20% at midnight, will be 25% at noon and 30% at midnight tonight. Moonrise is at 11:50 this morning. Moonset is at 21:20 tonight and moonrise is at 12:58 tomorrow morning. Moonlight time is 9 hours, 30 minutes which is 34 minutes shorter than yesterday.

Grandparent's Day is today. -Bernie-