October 17: ORD

Today is October 17th. It's the 290th day of the year. 75 days remain. It's week 42 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.

According to the National Climatic Data Center (NCDC), the normal high is 62 and the normal low is 42. I've calculated the 32-year averages at 61 and 42.

On the warm side, in 1994 the high was 78 with a low of 61. Four years later, in 1998, the high was 70 with the record warmest low of 63, a seven degree spread. As you can see, two of O'Hare's three lows in the 60s on October 17th occurred in the past 32 years. In 1990 the high was 78 with a low of 51. Other warm highs were 75 in 2005, 74 in 1991 and 74 in 1995. The record high of 86 was set in 1950 at Midway. 16 of the past 32 highs (50%) were in the: 40s (3) and 50s (13). 16 of the past 32 highs (50%) were in the: 60s (6) and 70s (10). Our most recent: 70s high was 72 in 2007 and 60s high was 65 last year, in 2010.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1977 the high was 67 with a low of 35, a 32 degree spread. In 1976 the high was 50 with a low of 29, a cold day. In 1972 the high was a cool 47 with a low of 31, a cool day. In 1971 the high was a warm 76 with a low of 51, a warm day. In 1968 the high was 77 with a low of 54, a warm day. In 1965 the high was 82 with a low of 62, a warm day. In 1964 the high was a warm 80 with a low of 43, a 37 degree spread. In 1963 the high was 76 with a low of 57, a warm day. In 1962 the high was 69 with a low of 37, a 32 degree spread. In 1961 the high was a warm 78 with a low of 53, a warm day.

More recently, there were large spreads of 34 degrees in 2005 (75/41) and 30 degrees two decades earlier in 1985 (72/42). There were no additional small spreads of up to seven degrees.

On the cool side, in 1992 the high was 49 with a low of 28, the only 20s low of the last 32 years and only the second one at O'Hare on October 17th (see 1976 above). A decade later, in 2002, the high was 45 with a low of 36. Another cool high was 47 in 1989. The record low of 26 was set in 1948 at Midway. The record coolest high of 40 occurred way back in 1880, a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 32 lows (81%) were in the: 30s (10) and 40s (16). One low was in the cold 20s. Five lows were in the warm: 50s (3) and 60s (2).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:40 and sunrise is at 7:08. Sunset is at 18:09 and twilight ends at 18:37. There's a total of 11 hours, 1 minute of daylight today and 11 hours, 57 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:41 and sunrise is at 7:09. The moon is waning gibbous and reaches last quarter in two days. Illumination was 78% at midnight, will be 74% at noon and 69% at midnight tonight. Moonset is at 12:19 this afternoon. Moonrise is at 21:45 tonight. Moonset is at 13:04 tomorrow afternoon. Moonlight time is 14 hours, 34 minutes which is 4 minutes shorter 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. United Nations Day is in seven days.