October 27: ORD

Today is October 27th. It's the 301st day of the year. 65 days remain. It's week 43 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 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 58 and the normal low is 40. I've calculated the 33-year averages at 58 and 40.

On the warm side, in 1984 (O'Hare's warmest October 27th) the high was 76 (O'Hare's co-hottest high of the date) with the record warmest low of 63. In 1998 the high was 70 with a low of 56. In 1989 the high was 76 (O'Hare's other co-hottest high of the date) with a low of 49. In 2000 the high was 71 (our most recent 70s high) with a low of 51. The other warm highs were 72 degrees in 1974 and 70 degrees in 1966. The other warm lows were 53 degrees in 2004 and 52 degrees in 1996. The record high of 83 degrees was set back in 1927 at the University of Chicago. 28 of the past 33 highs (85%) were in the: 40s (7), 50s (10) and 60s (11). Four highs were in the warm 70s. One high was in the cold 30s (O'Hare's only 30s high of 38 degrees in 1997). There have been no highs in the 80s in the history of O'Hare on this date! O'Hare's second warmest October 27th was in 1971 as the high was 74 (O'Hare's second hottest high of the date) with a low of 54. O'Hare's other warm 10/27 was in 1970 as the high was 67 with a low of 60 (O'Hare's second warmest low of the date). 

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1976 the high was 42 with a low of 23, a cold day. In 1974 the high was a warm 72 with a low of 38, a 34 degree spread. In 1971 the high was 74 with a low of 54, a warm day. In 1970 the high was 67 with a warm low of 60, a seven degree spread and warm day. In 1969 the high was 44 with a low of 28, a cold day. In 1967 the high was a cold 41 with a low of 34, a seven degree spread and cool day. In 1966 the high was a warm 70 degrees. In 1962 the high was 64 with a low of 34, a 30 degree spread. In 1961 the low was a cold 25 degrees. In 1959 the high was a cold 40 with a low of 33, a seven degree spread and cool day.

More recently, there were large spreads of 33 degrees in 1983 (65/32) and 32 degrees in 1982 (65/33). There were small spreads of six degrees in 1991 (53/47), six degrees three years ago, in 2009 (51/45), and seven degrees in 2006 (45/38).

On the cool side, in 1997 (O'Hare's coolest October 27th) the high was 38 (O'Hare's coolest high of the date) with a low of 26. In 1980 the high was 43 with a low of 27. In 2001 the high was 45 with a low of 30. The other cold low was O'Hare's second coldest low of 25 degrees in 1961. The other cold highs were 44 degrees in 2003, 45 degrees in 2006, 46 degrees in 1993 and 46 degrees in 2002. The record low of 24 degrees was set in 1942 at Midway. The record coolest high of 34 degrees was set in 1925, at a time when the official readings were taken adjacent to Lake Michigan. 17 of the last 33 lows (52%) were in the 30s. 14 lows (42%) were in the: 40s (9), 50s (4) and 60s (1). The four lows in the 50s occurred in a nine year span from 1996 through 2004. The lone 60s low is the current record warmest low of 63 degrees in 1984. Two lows (6%) were in the cold 20s (27 degrees in 1980 and 26 degrees in 1997). O'Hare's second coolest October 27th was in 1976 as the high was 42 with a low of 23 (O'Hare's coldest low of the date and a low that's colder than the record low). The other cool days were in: 1969 (high of 44, low of 28), 1959 (high of 40 (O'Hare's second coolest high of the date), low of 33)) and 1967 (high of 41, low of 34).   

There's two instances of back-to-back years in which temperatures were just about as opposite as they can be. In the first instance, in 1997 the high was 38 with a low of 26, overall 17 degrees BELOW normal. Then in 1998 the high was 70 with a low of 56, overall 14 degrees ABOVE normal. In the second instance, in 2000 the high was 71 with a low of 51, overall 12 degrees ABOVE normal. Then in 2001 the high was 45 with a low of 30, overall 11.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:52 and sunrise is at 7:21. Sunset is at 17:53 and twilight ends at 18:22. There's a total of 10 hours, 32 minutes of daylight today and 11 hours, 30 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:53 and sunrise is at 7:22. The moon is waxing gibbous, heading towards the full Hunter's moon in two days at 14:49. Illumination was 94% at midnight, will be 96% at noon and 98% at midnight tonight. Moonset was at 5:14 this morning. Moonrise is at 16:40 this afternoon. Moonset is at 6:15 tomorrow morning. Moonlight time is 12 hours, 34 minutes which is 33 minutes longer 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. Halloween is in four days. Standard Time returns in eight days. Election Day is in ten days.