October 6: ORD

Today is October 6th. It's the 280th day of the year. 86 days remain. It's week 40 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 66 and the normal low is 46. I've calculated the 33-year averages at 67 and 45.

On the warm side, in 2007 (O'Hare's warmest October 6th) the high was 87 with a low of 69 (O'Hare's warmest low of the date). In 1982 (O'Hare's third warmest October 6th) the high was 87 with a low of 61. Those highs of 87 degrees are O'Hare's second hottest highs of the date. In 1990 the high was 84 with a low of 60. In 1997 the high was 84 with a low of 56. The record high of 94 degrees was set in 1963 at Midway. The record warmest low of 70 degrees occurred way back in 1879, at a time when the official readings were taken adjacent to Lake Michigan. 27 of the past 33 highs (82%) were in the: 50s (9), 60s (9) and 70s (9). Five highs were in the hot 80s. One high was in the cold 40s (48 degrees in 2000). O'Hare's second warmest October 6th was in 1963 as the high was 91 (O'Hare's hottest high of the date) with a low of 58, a 33 degree spread. O'Hare's other warm high was 81 degrees last year, in 2011. 1970 was another warm October 6th as the high was 79 with a low of 60. Another warm low of 58 degrees occurred in 1959.  

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1970 the high was 79 with a low of 60, a warm day. In 1968 the high was 52 with a low of 48, a four degree spread. In 1966 the high was 67 with a cold low of 28, a 39 degree spread. That low of 28 is equal to the record low, set in 1952 at Midway. In 1964 the high was 52 with a low of 25, a cold day. That low of 25 is colder than the record low of 28, set in 1952 at Midway. In 1963 the high was 91 with a low of 58, a 33 degree spread and hot day. 1963 was the year of the record high of 94, set at Midway. In 1959 the low was a warm 58 degrees.

More recently, there were large spreads of 34 degrees in 1992 (70/36), 34 degrees in 1993 (78/44), 33 degrees in 1980 (70/37), 32 degrees two years ago, in 2010 (78/46) and 31 degrees last year, in 2011 (81/50). There were no small spreads of up to seven degrees. 

On the cool side, in 2001 (O'Hare's second coolest October 6th) the high was 50 (O'Hare's second coolest high of the date) with a low of 30. A year earlier, in 2000, the high was 48 (O'Hare's coolest high of the date) with a low of 34. In 1988 the high was 56 with a low of 30. In 1991 the high was 53 with a low of 35. The record low of 28 degrees and record coolest high of 46 degrees were set on the same cold day in 1952 at Midway. 30 of the last 33 lows (91%) were in the: 30s (11), 40s (11) and 50s (8). Our most recent 30s high is 35 degrees in 2003. Three lows were in the warm 60s. O'Hare's coolest October 6th was in 1964 as the high was 52 with a low of 25 (O'Hare's coldest low of the date and a low colder than the record low). O'Hare's other cold lows of the date are 28 degrees in 1966 (O'Hare's second coldest low of the date) and 32 degrees in 1985. O'Hare's other cool highs of the date are 52 degrees in 1968 and 54 degrees in 1987.

There's an instance of back-to-back years in which temperatures were just as opposite as they can be. In 1990 the high was 84 with a low of 60, overall 16 degrees ABOVE normal. Then in 1991 the high was 53 with a low of 35, overall 12 degrees BELOW normal.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:28 and sunrise is at 6:56. Sunset is at 18:25 and twilight ends at 18:53. There's a total of 11 hours, 29 minutes of daylight today and 12 hours, 25 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:29 and sunrise is at 6:58. The moon is waning gibbous and will reach last quarter in two days at 2:33. Illumination was 69% at midnight, will be 65% at noon and 60% at midnight tonight. Moonset is at 12:56 this afternoon. Moonrise is at 22:36 tonight. Moonset is at 13:39 tomorrow afternoon. Moonlight time is 14 hours, 20 minutes which is three minutes shorter than yesterday. Moonlight time is at its peak today, just as it was yesterday and Thursday.

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. Columbus Day is in two days. Standard Time doesn't return until November 4th.