October 10: ORD

Today is October 10th. It's the 284th day of the year. 82 days remain. It's week 41 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 65 and the normal low is 44. I've calculated the 33-year averages at 63 and 43.

On the warm side, two years ago, in 2010 (O'Hare's second warmest October 10th), the high was 84 (O'Hare's second hottest high of the date) with a low of 57. In 1999 the high was 79 with a low of 53. The record high of 86 degrees was set in 1962 at Midway. The record warmest low of 68 degrees occurred way back in 1879, a time when the official readings were taken adjacent to Lake Michigan. 22 of the past 33 highs (67%) were in the: 50s (8) and 60s (14). Seven highs (21%) were in the warm: 70s (6) and 80s (1). All of the 70s and 80s highs (post 1978) occurred between 1995 and 2011. Four highs (12%) were in the cold 40s (the two highs of 48 degrees in 1990 and three years ago in 2009). O'Hare's warmest October 10th was in 1973 as the high was 81 with a low of 65 (O'Hare's warmest low of the date). O'Hare's third warmest October 10th was in 1961 as the high was 80 with a low of 60 (O'Hare's second warmest low of the date). O'Hare's hottest high of the date of 87 degrees occurred in 1962. The other warm highs of the date are 82 degrees in 1963, 79 degrees in 1960 and 77 degrees in 2003. The other warm low is 56 degrees in 1984.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1978 the high was 62 with a low of 55, a seven degree spread. In 1974 the high was 70 with a low of 38, a 32 degree spread. In 1973 the high was 81 with a low of 65, a warm day. In 1967 the high was a cool 51 with a low of 36, a cool day. In 1964 the high was 48 with a low of 20 (cooler than the record low and year of the record low), a cold day. In 1963 the high was a warm 82 with a low of 50, a 32 degree spread and warm day. In 1962 the high was a hot 87 with a low of 43, a 44 degree spread. 1962 was the year of the record high (see above). In 1961 the high was 80 with a low of 60, a warm day. In 1960 the high was a warm 79 with a low of 47, a 32 degree spread.

More recently, there was a large spread of 30 degrees in 2008 (72/42). There were small spreads of six degrees in 2006 (58/52) and seven degrees in 2007 (54/47).

On the cool side, three years ago, in 2009 (O'Hare's second coolest October 10th), the high was 48 with a low of 31. In 1996 the high was 50 with a low of 31. In 1990 the high was 48 with a low of 34. In 1993 the high was 53 with a low of 30. In 1987 the high was 48 with a low of 37. O'Hare also had a high of 48 degrees in 1964. The highs of 48 degrees are the second coolest of the date. The lows of 31 degrees are O'Hare's third coldest of the date. The record low of 27 degrees was set in 1964 at Midway. The record coldest high of 39 degrees occurred way back in 1906, a time when the official readings were taken adjacent to Lake Michigan. 13 of the last 33 lows (40%) were in the 40s. 12 lows (36%) were in the cold 30s. Eight lows (24%) were in the warm 50s. Seven of those eight 50s lows (88%) occurred between 1999 and 2011. O'Hare's coolest October 10th was in 1964 as the high was 48 with a low of 20 (O'Hare's coldest low of the date and a low that's colder than the record low). O'Hare's other cool highs are 47 degrees in 1985 (O'Hare's coolest high of the date) and 51 degrees in 1967.

There's an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 2009 the high was 48 with a low of 31, overall 14.5 degrees BELOW normal. Then in 2010 the high was 84 with a low of 57, overall 16.5 degrees ABOVE normal.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:33 and sunrise is at 7:01. Sunset is at 18:19 and twilight ends at 18:47. There's a total of 11 hours, 18 minutes of daylight today and 12 hours, 14 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:34 and sunrise is at 7:02. The moon is waning crescent, having passed last quarter two days ago at 2:33. Illumination was 31% at midnight, will be 27% at noon and 22% at midnight tonight. Moonrise was at 1:32 this morning. Moonset is at 14:26 this afternoon. Moonrise is at 2:37 tomorrow morning. Moonlight time is 13 hours, 54 minutes which is 29 minutes shorter than yesterday.

Warm Fall began September 22nd and runs for 41 days through November 1st. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. United Nations Day is in 14 days. Standard Time doesn't return until November 4th.