September 14: ORD

Today is September 14th. It's the 257th day of the year. 108 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 76 and the normal low is 55. I've calculated the 32-year averages at 74 and 55.

On the hot side, in 1994 the high was 90 (our most recent 90s high) with a low of 73 (our only 70s low). Three years earlier, in 1991, the high was 90 with a low of 67. Another warm low was 68 in 1998. The record high of 99 and record warmest low of 76 were set on the same hot day back in 1939. 16 of the past 32 highs (50%) were in the 70s. Seven highs (22%) were in the hot: 80s (5) and 90s (2). Nine highs (28%) were in the cool 60s.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1975 the low was a cold 41 degrees. In 1974 the low was a cold 40 degrees, equal to the record low. In 1971 the high was a hot 90 with a low of 58, a 32 degree spread. In 1970 the high was a cool 59 with a low of 55, a four degree spread. In 1969 the low was a warm 68 degrees. In 1964 the high was 80 with a cold low of 42, a 38 degree spread. In 1963 the high was 70 with a cold low of 38, a 32 degree spread. That low of 38 was colder than the record low. In 1961 the high was a cool 63 degrees.

More recently, there were large spreads of 31 degrees in 1988 (81/50), 30 degrees in 1987 (76/46) and 30 degrees in 2002 (83/53). There was a small spread of seven degrees in 1998 (75/68). Three years ago, in 2008, we received more rain from the remnants of Hurricane Ike. O'Hare recorded 1.44 inches. Cincinnati had a peak wind gust of 74 miles an hour, causing power outages.

On the cool side, in 1996 the high was 60 with a low of 46. In 1985 the high was 69 with the record low of 40. Another cool high was 63 in 2001. The record coolest high of 54 occurred way back in 1923, a time when the official readings were taken adjacent to Lake Michigan. 18 of the last 32 lows (56%) were in the 50s. Eight lows (25%) were in the cold 40s. Six lows (19%) were in the warm: 60s (5) and 70s (1). Our most recent 60s low was 64 in 2004.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:04 and sunrise is at 6:32. Sunset is at 19:05 and twilight ends at 19:33. There's a total of 12 hours, 33 minutes of daylight today and 13 hours, 29 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:05 and sunrise is at 6:33. The moon is waning gibbous and was full two days ago as the full Harvest (a.k.a. Barley) moon at 4:27. Illumination was 97% at midnight, will be 95% at noon and 93% at midnight tonight. Moonset is at 8:47 this morning. Moonrise is at 19:45 tonight. Moonset is at 9:47 tomorrow morning. Moonlight time is 13 hours, 2 minutes which is 33 minutes longer than yesterday.

Summer began June 4 and runs for 110 days through September 21. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Citizenship Day is in three days.