October 25: ORD

Today is October 25th. It's the 299th day of the year. 67 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 59 and the normal low is 40. I've calculated the 33-year averages at 58 and 39.

On the warm side, in 1989 (O'Hare's warmest October 25th) the high was 77 (tied with 1989 as O'Hare's hottest high of the date) with a low of 52. Two years ago, in 2010 (tied with 1963 and 1971 as O'Hare's second warmest October 25ths), the high was 72 with a low of 56 (O'Hare's second warmest low of the date). In 2000 the high was 69 with a low of 55. The other hot highs were 76 degrees in 1964 (O'Hare's second hottest high of the date), 75 degrees in 2004 and 74 degrees last year, in 2011. The other warm low was 52 degrees in 1986. The record high of 79 degrees and record warmest low of 62 degrees were set in on the same warm day in 1963 at Midway. 27 of the past 33 highs (82%) were in the: 40s (7), 50s (10) and 60s (10). Our most recent 40s highs were 40 degrees in 2001 and 47 degrees in 2002. Five highs were in the warm 70s. One high was in the cold 30s. There were no 80s highs on this date in O'Hare's history or in the history of Chicago record-keeping. The two years that are tied with 2010 as O'Hare's second warmest October 25ths are 1963 (high of 77 (tied with 1989 as O'Hare's hottest high of the date), low of 51) and 1971 (high of 69, low of 59 (O'Hare's 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 1971 the high was 69 with a warm low of 59, a warm day. In 1967 the high was a cold 44 with a low of 38, a six degree spread. In 1966 the high was 57 with a cold low of 26, a 31 degree spread. In 1964 the high was a warm 76 with a low of 41, a 35 degree spread. In 1963 the high was a warm 77 with a low of 51, a warm day and year of the record high of 79 and record warmest low of 62 (records set at Midway). In 1962 the high was 38 with a low of 21, a cold day. In 1959 the high was a cold 40 with a low of 35, a five degree spread and cold day. 

More recently, there was a large spread of 37 degrees in 2004 (75/38), 36 degrees in 1982 (62/26), 31 degrees in 1985 (67/36), 30 degrees in 1996 (68/38) and 30 degrees in 1999 (65/35). There were small spreads of three degrees in 1986 (55/52), four degrees in 1997 (49/45), five degrees in 1994 (46/41) and five degrees in 2002 (47/42).

On the cold side, in 1988 (O'Hare's second coolest October 25th) the high was 43 with a low of 26. In 1980 the high was 39 (O'Hare's second coolest high of the date) with a low of 33, a six degree spread. In 2001 the high was 40 with a low of 35, a five degree spread. In 1979 the high was 46 with a low of 31. The other cold lows were 26 degrees in both 1966 and 1982. The other cool highs were 44 degrees in 1967, 45 degrees in 1981, 46 degrees in 1994 and 47 degrees in 2002. The record low of 14 degrees and record coldest high of 29 degrees were set on the same cold day way back in 1887, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 30s (14) and 40s (11). There were ten consecutive 30s and 40s lows from 1990 through 1999. Our most recent 30s lows were each 38 degrees in 2004 and 2005. Four lows (12%) were in the cold 20s. Four lows (12%) were in the warm 50s. O'Hare's coolest October 25th was in 1962 as the high was 38 (O'Hare's coolest high of the date) and low of 21 (O'Hare's coldest low of the date). Another cool day was in 1959 as the high was 40 with a low of 35. To summarize, O'Hare's second coldest lows were 26 degrees in 1966, 1982 and 1988.

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 1988 the high was 43 with a low of 26, overall 15.5 degrees BELOW normal. Then in 1989 the high was 77 with a low of 52, overall 14.5 degrees ABOVE normal. In the second instance, in 2000 the high was 69 with a low of 55, overall 12 degrees ABOVE normal. Then in 2001 the high was 40 with a low of 35, overall 12.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:50 and sunrise is at 7:18. Sunset is at 17:56 and twilight ends at 18:24. There's a total of 10 hours, 38 minutes of daylight today and 11 hours, 34 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:51 and sunrise is at 7:20. The moon is waxing gibbous. Illumination was 81% at midnight, will be 85% at noon and 88% at midnight tonight. Moonset was at 3:10 this morning. Moonrise is at 15:45 this afternoon. Moonset is at 4:13 tomorrow morning. Moonlight time is 11 hours, 25 minutes which is 35 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 six days. Standard Time returns in ten days. Election Day is in 12 days.