September 19: ORD

Today is September 19th. It's the 263rd day of the year. 103 days remain. It's week 38 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. Before this, the official site of record was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. Before this, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 74 and the normal low is 53. I've calculated the 33-year averages at 75 and 55.

On the warm side, in 1985 (tied as O'Hare's third warmest September 19th with 1963) the high was 87 with a low of 66. In 2002 the high was 80 with a low of 72 (O'Hare's warmest low of the date). Two years earlier, in 2000, the high was 87 with a low of 62. Five years later, in 2005, the high was 84 with a low of 65. Two years later, in 2007, the high was 84 with a low of 65. O'Hare's hottest highs of the date are 87 degrees in 1974, 1984, 1985 and 2000. The record high of 93 degrees was set in 1955 at Midway. The record warmest low of 74 degrees occurred way back in 1908, a time when the official readings were taken adjacent to Lake Michigan. 31 of the past 33 highs (94%) were in the: 60s (8), 70s (10) and 80s (13). Two highs were in the cool 50s. High temps tend to be unpredictable on September 19th. The past two years (2010 and '11) had highs of 67 and 69 degrees. But the two years prior (2008 and '09) had highs of 77 and 76 degrees. Then 2005 & 2007 had highs of 84 degrees  but between was a high of only 55 degrees in 2006! Before that, we had highs of 80, 67 and 79 degrees in 2002, '03 and '04. So as you can see, highs jump around a lot. O'Hare's warmest September 19th was in 1978 as the high was 90 (tied with 1963 as O'Hare's hottest high of the date) with a low of 67. O'Hare's second warmest 9/19 was in 1965 as the high was 86 with a low of 68 (O'Hare's second warmest low of the date). Tied with 1985 as O'Hare's third warmest 9/19 is 1963 with a high of 90 (tied with 1978 as O'Hare's hottest high of the date) with a low of 63. O'Hare also had a hot high of 87 degrees in 1974 and a warm low of 65 degrees in 1967.    

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 67, a hot day. In 1976 the high was 82 with a low of 47, a 35 degree spread. In 1974 the high was a hot 87 degrees. In 1968 the high was a cool 62 with a low of 59, a three degree spread. In 1967 the low was a warm 65 degrees. In 1965 the high was 86 with a low of 68, a hot day. In 1963 the high was a hot 90 with a low of 63, a hot day. In 1962 the low was a cold 39 degrees, colder than the record low of 40.

More recently, there were large spreads of 34 degrees in 1984 (87/53), 33 degrees in 1999 (80/47) and 30 degrees in 1994 (85/55). There were no small spreads of up to seven degrees.

On the cool side, in 1991 (O'Hare's coolest September 19th) the high was 56 (O'Hare's second coolest high of the date) with the record low of 40 (O'Hare's second coldest low of the date). In 2006 (O'Hare's second coolest September 19th) the high was 55 (O'Hare's coolest high of the date) with a low of 47. The other cool highs of 62 degrees occurred in 1968 and again in 1990. O'Hare's third coldest low of 42 degrees occurred in 1992. The record coolest high of 52 degrees was set in 1938 at the University of Chicago. 17 of the last 33 lows (52%) were in the 50s. Eight lows (24%) were in the cold 40s. Eight lows (24%) were in the warm: 60s (7) and 70s (1). O'Hare's coldest low of the date of 39 degrees occurred in 1962. Although this low is colder than the record low, O'Hare was not the station of record for Chicago at the time.

There were back-to-back-to-back years in which temperatures were just as opposite as can be. In 2005 the high was 84 with a low of 65, overall 11.5 degrees ABOVE normal. Then in 2006 the high was 55 with a low of 47, overall 12 degrees BELOW normal. Then in 2007 the high was 84 with a low of 65, overall 11.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:10 and sunrise is at 6:38. Sunset is at 18:55 and twilight ends at 19:23. There's a total of 12 hours, 17 minutes of daylight today and 13 hours, 13 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:11 and sunrise is at 6:39. The moon is waxing crescent. Illumination was 13% at midnight, will be 17% at noon and 22% at midnight tonight. Moonrise is at 10:54 this morning. Moonset is at 20:58 tonight. Moonrise is at 12:04 tomorrow afternoon. Moonlight time is 10 hours, 4 minutes which is 29 minutes shorter than yesterday.

Summer began on June 4th and runs for 110 days through September 21st. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. The Autumnal Equinox is in three days on Saturday the 22nd at 9:49. Columbus Day is in 19 days. Standard Time doesn't return until November 4th.