September 2: ORD

Today is September 2nd. It's the 245th day of the year. 120 days remain. It's week 35 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 78 and the normal low is 58. I've calculated the 31-year averages at 80 and 59.

On the hot side, two years ago the high was 94 with a low of 65. Other 90s highs were 91 in 2000 and 90 in 1999. There was one 70s low. That was 70 in 1979. The record high of 101 was set in 1953. The record warmest low of 78 was set back in 1913. Over the last 31 years, 27 highs (87%) were: 70s (12) and 80s (15). Three highs were in the warmer 90s. One high was in the cooler 60s.

In reference to yesterday, September 1, 2010, the low was 71 at 9:09. This was the first low of 70 or higher in 37 years and just the third low of 70 or higher in the history of O'Hare on the first of September. 37 years ago in 1973 the low was 73. The record warmest low of 76 was set at Midway on the same day. The first 70s low at O'Hare was also 73 degrees, occurring in 1960.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1974 the high was a cool 58 with a low of 48, a cool day. That high of 58 was cooler than the record coolest high. In 1973 the high was 91 with a low of 73, a hot day. In 1971 the high was 90 with a low of 71, a hot day. In 1967 the high was 73 with a low of 40, a 33 degree spread and cool day. That low of 40 was cooler than the record low. In 1966 the high was a hot 90. In 1964 the high was 81 with a low of 49, a 32 degree spread. In 1962 the high was 82 with a low of 52, a 30 degree spread. In 1960 the high was 89 with a warm low of 72, a hot day.

More recently, there were large spreads of 33 degrees in 1999 (90/57) and 30 degrees in 1983 (88/58). There were no small spreads (up to seven degrees).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. 1994 was the coolest day with a high of 68 (one of only three highs below 70 degrees in O'Hare's history. The others were highs of 58 in 1974 and another 68 in 1972) and one of our two lows of 49. The other low of 49 occurred in 2001. Even cooler, the record low of 44 was set back in 1946. The record coolest high of 63 occurred back in 1935. Over the last 31 years, 28 lows (90%) were: 50s (12) and 60s (16). Two lows were in the cooler 40s and one low was in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:51 and sunrise is at 6:20. Sunset is at 19:25 and twilight ends at 19:54. There's a total of 13 hours, 5 minutes of daylight today and 14 hours, 3 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 5:52 and sunrise is at 6:21. The moon reached last quarter yesterday at 12:22 and is waning crescent. Illumination was 45% at midnight, will be 39% at noon and 34% at midnight tonight. Moonset is at 15:17 this afternoon and moonrise is at 24 minutes past midnight tonight. Moonset is at 16:09 tomorrow afternoon. Moonlight time is 15 hours, 17 minutes which is 22 minutes longer than yesterday.

Labor Day is in four days and Patriot Day is in nine days. -Bernie-