May 24: ORD

Today is May 24th. It's the 145th day of the year. 221 days remain. It's week 21 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 73 and the normal low is 51. I've calculated the 33-year averages at 70 and 50.

On the warm side, two years ago, in 2010 (O'Hare's warmest May 24th), the high was 91 (along with the high of 91 in 1977, O'Hare's warmest highs of the date) with the new record warmest low of 70. In 1991 the high was 85 with the former record warmest low of 68. In 1933 the low was 67 which is another former record warmest low. In 1989 the high was 86 with a low of 65. In 2007 the high was 88 with a low of 63. The record high of 93 was last tied in 1950 at Midway, having originally been set in 1921. 21 of the past 33 highs (64%) were in the: 60s (11) and 70s (10). There were nine consecutive highs in the 60s & 70s from 1978 through 1986. Seven of these (78%) were in the 70s. Seven highs (21%) were in the warm: 80s (6) and 90s (1). Five highs (15%) were in the cool: 40s (1) and 50s (4). O'Hare's second warmest May 24th was in 1977 as the high was 91 (it was also 91 two years ago in 2010) with a low of 64.

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1977 the high was 91 with a low of 64, a hot day. In 1976 the high was a cool 60 degrees. In 1975 the high was a warm 85 with a low of 62, a warm day. In 1972 the high was a hot 86 with a low of 54, a 32 degree spread. In 1965 the high was 83 with a low of 53, a 30 degree spread. In 1961 the high was 80 with a low of 45, a 35 degree spread. In 1960 the high was a cool 60 degrees.

More recently, there were large spreads of 34 degrees in 1985 (78/44), 32 degrees in 1983 (76/44), 31 degrees in 1997 (84/53) and 31 degrees in 2006 (80/49).

On the cool side, in 1992 (O'Hare's coolest May 24th) the high was 46 (O'Hare's coolest high of the date) with the record low of 34. In 2001 the high was 60 with a low of 42. Two years earlier, in 1999, the high was 54 with a low of 48, a six degree spread. Two decades earlier, in 1979, the high was 62 with a low of 40. The other cool highs were 61 in 1982, 57 in 1995, 56 in 1987 and 56 in 1996. The record coolest high of 44 occurred back in 1925, at a time when the official readings were taken adjacent to Lake Michigan. 28 of the last 33 lows (85%) were in the: 40s (18) and 50s (10). One low was in the cold 30s. Four lows were in the warm: 60s (3) and 70s (1).

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1991 the high was 85 with a low of 68,  overall 14.5 degrees ABOVE normal. Then in 1992 the high was 46 with a low of 34, overall 22 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:51 and sunrise is at 5:24. Sunset is at 20:17 and twilight ends at 20:50. There's a total of 14 hours, 53 minutes of daylight today and 15 hours, 59 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:50 and sunrise is at 5:23. The moon is waxing crescent. Illumination was 10% at midnight, will be 13% at noon and 16% at midnight tonight. Moonrise was at 8:24 this morning. Moonset is at 23:16 tonight. Moonrise is at 9:24 tomorrow morning. Moonlight time is 14 hours, 52 minutes which is 17 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. Memorial Day is in four days.