May 30: ORD

Today is May 30th. It's the 151st day of the year. 215 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 53. I've calculated the 33-year averages at 78 and 55.

On the hot side, in 2006 (O'Hare's warmest May 30th) the high was 89 with a low of 67. In 1991 the high was 88 with a low of 66. Three years later, in 1994, the high was 90 with a low of 64. In 1987 the high was 85 with a low of 68. Two decades later, in 2007, the high was 87 with a low of 66. In 1980 the high was 86 with a low of 66. Three decades later (two years ago, in 2010), the high was 91 with a low of 61, a 30 degree spread. In 1988 the high was 91 with a low of 60, a 31 degree spread. Those highs of 91 in 1988 and 2010 are O'Hare's warmest highs of the date. The other warm highs were 88 last year, in 2011 and 87 in 1998. The record high of 93 was set in 1942 at the University of Chicago and tied in 1953 at Midway. The record warmest low of 72 occurred back in 1921, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the past 33 highs (88%) were in the: 60s (7), 70s (8) and 80s (14). Our most recent 60s high was 60 in 2001. Three highs were in the hot 90s. One high was in the cool 50s (55 in 1983).

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1971 the high was 82 with a low of 45, a 37 degree spread. In 1970 the low was a warm 68 degrees. In 1964 the high was 69 with a cold low of 34, a 35 degree spread and cool day. In 1963 the high was 74 with a cold low of 41, a 33 degree spread. In 1962 the low was a warm 67 degrees. In 1961 the high was 76 with a cold low of 37, a 39 degree spread.

More recently, there were additional large spreads of 31 degrees in 1984 (70/39) and 31 degrees in 2000 (80/49).

On the cool side, in 1983 the high was the only 50s high for the date at 55 degrees with a low of 45. In 1996 the high was 65 with a low of 36. Five years later, in 2001, the high was 60 with a low of 45. The other cold low was 39 in 1984. Both records were set way back in the 19th century, at a time when the official readings were taken adjacent to Lake Michigan. The record low of 35 was set way back in 1873. The record coolest high of 42 occurred way back in 1889. 31 of the last 33 lows (94%) were in the: 40s (9), 50s (10) and 60s (12). Two lows were in the cold 30s. Prior to 1979, O'Hare had cold lows of 34 in 1964, 37 in 1961 and 41 in 1963.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:47 and sunrise is at 5:20. Sunset is at 20:22 and twilight ends at 20:56. There's a total of 15 hours, 2 minutes of daylight today and 16 hours, 9 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:46 and sunrise is at 5:20. The moon is waxing gibbous, having reached first quarter two days ago at 15:16. Illumination was 65% at midnight, will be 71% at noon and 76% at midnight tonight. Moonset was at 1:51 this morning. Moonrise is at 14:55 this afternoon. Moonset is at 2:22 tomorrow morning. Moonlight time is 10 hours, 56 minutes which is 40 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 15 days.