October 15: ORD

Today is October 15th. It's the 289th day of the year. 77 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. 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 63 and the normal low is 43. I've calculated the 33-year averages at 63 and 44.

On the warm side, in 1989 (O'Hare's second warmest October 15th) the high was 83 with a low of 60. The year earlier, in 1988, saw a high of 76 with a low of 55. The other warm highs were 84 degrees in 1963, 79 degrees in 1999, 78 degrees in 1996, 77 degrees in 1971 and 75 degrees in 1987. The record high of 88 degrees was set in 1947 at Midway. The record warmest low of 69 degrees occurred way back in 1897, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the past 33 highs (91%) were in the: 50s (8), 60s (14) and 70s (8). One high was in the warm 80s. Two highs were in the cold 40s. There's a tie for O'Hare's warmest October 15th between 1962 and 1968. In 1962 the high was 87 (O'Hare's hottest high of the date) with a low of 64 (O'Hare's second warmest low of the date). In 1968 the high was 84 with a low of 67 (O'Hare's warmest low of the date). The highs of 84 degrees (in 1963 and 1968) are O'Hare's second hottest highs of the date. Another warm day was in 1965 as the high was 74 with a low of 58.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1978 the high was 52 with a cold low of 31, a cool day. In 1972 the high was 51 with a low of 31, a cold day. In 1971 the high was a warm 77 degrees. In 1968 the high was 84 with a low of 67, a warm day. In 1965 the high was 74 with a warm low of 58, a warm day. In 1964 the high was 74 with a low of 33, a large 41 degree spread. In 1963 the high was a warm 84 with a low of 35, a huge 49 degree spread. In 1962 the high was 87 with a low of 64, a hot day. In 1961 the high was 71 with a low of 37, a 34 degree spread.

More recently, there were large spreads of 38 degrees in 1983 (73/35) and 31 degrees in 1999 (79/48). There were small spreads of two degrees in 1992 (51/49) and three degrees to years ago, in 2009 (44/41).

On the cool side, in 1991 (O'Hare's coolest October 15th) the high was 49 (O'Hare's second coolest high of the date) with a low of 32. In 2006 (tied with 1978 as O'Hare's third coolest October 15th) the high was 52 with a low of 31. The record low of 28 degrees was set way back in 1876, at a time when the official readings were taken adjacent to Lake Michigan. The record coolest high of 44 degrees first occurred in 1943 and was tied three years ago in 2009. 25 of the last 33 lows (76%) were in the cold: 30s (11) and 40s (14). O'Hare recorded ten consecutive 30s and 40s lows from 1997 through 2006. Eight lows (24%) were in the warm: 50s (7) and 60s (1). O'Hare's second coolest October 15th was in 1972 as the high was 51 with a low of 31. Tied with 2006 as O'Hare's third coolest October 15th is 1978 with a high of 52 and low of 31. 1992 was a unique day. The high was a cool 51 degrees with a low of 49, just a two degree spread. The warm low kept the day from being one of the coolest. Another cold low of 31 degrees occurred in 1997. The lows of 31 degrees are O'Hare's coldest of the date, also occurring in 1972, 1978 and 2006.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:38 and sunrise is at 7:07. Sunset is at 18:11 and twilight ends at 18:39. There's a total of 11 hours, 4 minutes of daylight today and 12 hours, 1 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:39 and sunrise is at 7:08. The moon is new today at 7:02. Illumination was 0% at midnight, will be 0% at noon and 1% at midnight tonight. Moonrise was at 7:19 this morning. Moonset is at 18:09 tonight. Moonset is at 8:34 tomorrow morning. Moonlight time is 10 hours, 50 minutes which is 36 minutes shorter 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. United Nations Day is in nine days. Standard Time doesn't return until November 4th.