October 31: ORD

Today is October 31st. It's the 304th day of the year. 61 days remain. It's week 44 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. Before that, 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 56 and the normal low is 39. I've calculated the 32-year averages at 59 and 42.

On the warm side, in 1979 the high was 75 with a low of 53. Two years later, in 1981, the high was 72 with a low of 54. In 1997 the high was 65 with a low of 54. Four years later, in 2001, the high was 68 with a low of 50. Three years ago, in 2008, the high was 70 with a low of 48. In 2000 the high was 70 with a low of 47. The other warm highs were 73 in 1990 and 69 in 1999. The other warm lows were 54 in 1998 and 51 in 1982. The record high of 84 was set in 1950 at Midway. The record warmest low of 65 occurred in 1974 at Midway. 23 of the past 32 highs (72%) were in the: 50s (13) and 60s (10). There were eight consecutive 50s & 60s highs from 1982 through 1989. Additionally, five highs were in the warm 70s and four were in the cold 40s. Extremes of the highs happened recently as the high in 2008 was 70 while the high in 2009 was 46.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1974 the high was 77 with a low of 65, a warm day and year of the record warmest low, also 65 at Midway. In 1973 the high was 49 with a low of 42, a seven degree spread. In 1972 the high was 46 with a low of 44, a two degree spread. In 1969 the high was 50 with a low of 47, a three degree spread. In 1968 the high was a warm 79 with a low of 42, a 37 degree spread and warm day. In 1967 the high was 51 with a low of 49, a two degree spread. In 1964 the high was 67 with a low of 29, a 38 degree spread. In 1959 the high was 50 with a low of 46, a four degree spread.

More recently, the large spread was 31 degrees in 1990 (73/42). There were small spreads of five degrees in 1998 (59/54) and seven degrees in 2005 (57/50).

On the cold side, in 1996 the high was 40 with a low of 26. Three years earlier, in 1993, the high was 44 with a low of 25. The other cold low was 26 in 1988. The record low of 23 and record coldest high of 31 occurred on the same cold, winter-like day way back in 1873, a time when the official readings were taken adjacent to Lake Michigan. 22 of the last 32 lows (69%) were in the: 30s (10) and 40s (12). Three lows were in the cold 20s and seven were in the warm 50s. The 20s lows occurred in a nine year period between 1988 and 1996. The most recent 50s low was 50 in 2005. For 14 years (from 1983 through 1996) lows were below 50 degrees.

There's an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1996 the high was 40 with a low of 26, overall 14 degrees BELOW normal. Then in 1997 the high was 65 with a low of 54, overall 12.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:56 and sunrise is at 7:25. Sunset is at 17:48 and twilight ends at 18:18. There's a total of 10 hours, 23 minutes of daylight today and 11 hours, 22 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:57 and sunrise is at 7:26. The moon is waxing crescent and will reach first quarter in two days at 11:38. Illumination was 25% at midnight, will be 30% at noon and 35% at midnight tonight. Moonrise is at 12:34 this afternoon. Moonset is at 22:23 tonight. Moonrise is at 13:13 tomorrow afternoon. Moonlight time is 9 hours, 49 minutes which is 19 minutes longer than yesterday.

Warm Fall began September 22 and runs for 41 days through November 1. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. Halloween is today. Election Day is in eight days. Veterans Day is in 11 days.