May 29: ORD

Today is May 29th. It's the 150th day of the year. 216 days remain. It's week 22 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 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 74 and the normal low is 52. I've calculated the 33-year averages at 75 and 53.

On the warm side, in 2006 (O'Hare's warmest May 29th) the high was 91 (O'Hare's warmest high of the date) with a low of 68. In 1991 (O'Hare's second warmest May 29th) the high was 87 with the record warmest low of 71. The former record warmest low of 70 occurred in 1962. In 1987 the high was 89 with a low of 66. In 1999 the high was 86 with a low of 65. The other hot highs were 89 in 1988 and 88 in 2007. The other warm low was 64 in 1998. The record high of 95 was set back in 1942 at the University of Chicago. 31 of the past 33 highs (94%) were in the: 60s (11), 70s (8) and 80s (12). One high was in the cool 50s and one was in the hot 90s.

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1978 the high was a hot 88 with a low of 63, a hot day. In 1977 the high was 89 with a low of 64, a hot day. In 1973 the high was a cool 55 with a low of 46, a cool day. In 1972 the low was a warm 64 degrees. In 1971 the high was 75 with a low of 41, a 34 degree spread. In 1970 the high was 85 with a warm low of 67, a warm day. In 1967 the high was a cool 62 degrees. In 1966 the high was 62 with a low of 35, a cool day. In 1965 the high was 55 with a low of 32, a cold day. In 1964 the high was 60 with a low of 36, a cool day. In 1962 the high was 87 with a low of 68, a hot day. 1962 was the year of the former record warmest low of 70. In 1961 the high was 62 with a low of 40, a cool day.

More recently, there was a small spread of seven degrees in 1997 (62/55). There were large spreads of 37 degrees in 1979 (82/45), 33 degrees in 1992 (72/39), 31 degrees in 1985 (75/44) and 30 degrees in 1988 (89/59).
 
On the cool side, in 1984 (O'Hare's second coolest May 29th) we had the only 50s high of 57 with the record-tying low of 37. The record low of 37 was originally set in 1965. In 1996 the high was 60 with a low of 40. Three years earlier, in 1993, the high was 61 with a low of 41. The other cool highs were 62 in 1997, 62 in 2001 and 63 in 1990. The other cold low was 39 in 1992. The record coolest high of 46 occurred way back in 1889, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 40s (12), 50s (10) and 60s (8). Two lows were in the cold 30s and one was in the warm 70s. O'Hare's coolest May 29th was in 1965 as the high was 55 (O'Hare's coolest high of the date) and low of 32. Three consecutive lows (36 in 1964, 32 in 1965 and 35 in 1966) were colder than the record low.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:47 and sunrise is at 5:21. Sunset is at 20:21 and twilight ends at 20:55. There's a total of 15 hours of daylight today and 16 hours, 8 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:47 and sunrise is at 5:20. The moon is waxing gibbous, having reached first quarter yesterday at 15:16. Illumination was 55% at midnight, will be 60% at noon and 65% at midnight tonight. Moonset was at 1:21 this morning. Moonrise is at 13:45 this afternoon. Moonset is at 1:51 tomorrow morning. Moonlight time is 11 hours, 36 minutes which is 39 minutes shorter than yesterday. 

Spring began on March 12th and runs for 84 days through June 3rd. Warm Spring began on April 13th and runs for 52 days through June 3rd. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 80s and 90s occur infrequently. Flag Day is in 16 days.