September 28: ORD

Today is September 28th. It's the 272nd day of the year. 94 days remain. It's week 39 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 70 and the normal low is 49. I've calculated the 33-year averages at 68 and 49.

On the warm side, in 1986 (O'Hare's second warmest September 28th) the high was 82 with a low of 65 (O'Hare's second warmest low of the date). A year later, in 1987, the high was 82 with a low of 56. O'Hare's third hottest high of the date is 83 degrees in 1979. The record high of 92 degrees was set in 1953. The record warmest low of 71 degrees occurred in 1971. Both records were set at Midway. 22 of the past 33 highs (67%) were in the: 60s (13) and 70s (9). Five highs (15%) were in the warm 80s. Our most recent 80s high was 81 degrees in 1995. Six highs (18%) were in the cool 50s. O'Hare's warmest September 28th was in 1971 as the high was 89 (O'Hare's hottest high of the date) with a low of 73 (O'Hare's warmest low of the date). O'Hare's third warmest September 28th was in 1959 as the high was 77 with a low of 64 (with 1973, O'Hare's third warmest low of the date). O'Hare's second hottest high of the date of 87 degrees occurred in 1963. The other warm low of 64 degrees occurred in 1973 (tied as O'Hare's third warmest low of the date with 1959).

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1975 the high was 73 with a low of 40, a 33 degree spread. In 1973 the low was a warm 64 degrees. In 1971 the high was 89 with a low of 73, a hot day and year of the record warmest low. In 1967 the high was a cool 53 with a low of 41, a cool day. In 1964 the high was 62 with a cold low of 32, a 30 degree spread and cool day. In 1963 the high was a hot 87 with a low of 53, a 34 degree spread. In 1961 the high was 56 with a low of 33, a cool day. In 1959 the high was 77 with a warm low of 64, a warm day.

More recently, there were large spreads of 32 degrees in 1979 (83/51), 32 degrees in 1989 (74/42) and 31 degrees in 1985 (76/45). There were small spreads of four degrees in 2001 (56/52) and seven degrees in 1988 (65/58). 

On the cool side, in 1984 (O'Hare's second coolest September 28th) the high was 56 with a low of 36. In 2006 the high was 59 with a low of 40. The record low of 29 degrees was set in 1942 at Midway. The record coolest high of 50 degrees was set way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the last 33 lows (88%) were in the: 40s (12) and 50s (17). For an ongoing 20 consecutive years, beginning in 1992, lows have been in the 40s and 50s. Three lows were in the cold 30s. One low was in the warm 60s. O'Hare's coolest September 28th was in 1961 as the high was 56 with a low of 33 (O'Hare's second coldest low of the date). There's a tie for O'Hare's third coolest September 28th. In 1964 the high was 62 with a low of 32 (O'Hare's coldest low of the date). In 1967 the high was 53 (O'Hare's coolest high of the date) with a low of 41. O'Hare's second coolest highs of the date were 56 degrees in 1961, 1984 and 2001.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:20 and sunrise is at 6:48. Sunset is at 18:39 and twilight ends at 19:07. There's a total of 11 hours, 51 minutes of daylight today and 12 hours, 47 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:21 and sunrise is at 6:49. The moon is waxing gibbous, heading towards the full Harvest moon tomorrow at 22:19. Illumination was 96% at midnight, will be 98% at noon and 99% at midnight tonight. Moonset was at 5:18 this morning. Moonrise is at 17:42 this afternoon. Moonset is at 6:21 tomorrow morning. Moonlight time is 11 hours, 36 minutes which is 36 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. Columbus Day is in ten days. Standard Time doesn't return until November 4th.