May 23: ORD

Today is May 23rd. It's the 144th day of the year. 222 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 72 and the normal low is 50. I've calculated the 33-year averages at 71 and 50.

On the warm side, two years ago, in 2010, the high was 89 with a low of 62. Three years prior, in 2007, the high was 89 with a low of 60. In 1991 the high was 82 with a low of 66. The record high of 92 was set in 1977 at Midway. It was also 92 in 1921 and 1964. The record warmest low of 71 occurred in 1964 at Midway. 21 of the past 33 highs (64%) were in the: 60s (10) and 70s (11). Our most recent 60s high was 64 in 2003. Eight highs (24%) were in the warm 80s. Four highs (12%) were in the cool 50s. O'Hare's warmest May 23rd was in 1964 as the high was 88 with a low of 70 (O'Hare's warmest low of the date). The second warmest was in 1977 as the high was 91 (O'Hare's warmest high of the date) with a low of 66. 

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 66, a hot day and year of the record high. In 1976 the high was a cool 59 degrees. In 1975 the high was a warm 85 with a low of 60, a warm day. In 1973 the high was a cool 59 degrees. In 1972 the high was a warm 84 degrees. In 1968 the high was a cool 55 with a low of 52, a three degree spread. In 1967 the high was 72 with a low of 40, a 32 degree spread. In 1966 the high was a warm 85 degrees. In 1964 the high was 88 with a low of 70, a hot day and year of the record warmest low. In 1963 the high was 60 with a low of 32, a cool day. In 1962 the low was a warm 64 degrees. In 1961 the high was 67 with a cold low of 35, a 32 degree spread. In 1959 the high was a cool 56 degrees.

More recently, there were large spreads of 37 degrees in 2006 (75/38), 33 degrees in 1985 (73/40), 32 degrees in 1997 (73/41) and 30 degrees three years ago in 2009 (80/50).
 
On the cool side, in 1987 the high was 55 (along with a high of 55 in 1968, O'Hare's coolest highs of the date) with a low of 47. In 2008 the high was 57 with a low of 46. The other cool highs were 57 in 1982 and 58 in 1988. The only low in the 30s from 1979 onward was 38 in 2006. That low of 38 was just a degree warmer than the record low. The record low of 37 was set back in 1917, at a time when the official readings were taken adjacent to Lake Michigan. The record coolest high of 50 occurred back in 1931 at the University of Chicago. 27 of the last 33 lows (82%) were in the: 40s (16) and 50s (11). One low was in the cold 30s. Five lows were in the warm 60s. O'Hare's coolest May 23rd was in 1963 as the high was 60 with a low of 32 (O'Hare's coldest low of the date). O'Hare's only other 30s low of the date was 35 in 1961.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:52 and sunrise is at 5:25. Sunset is at 20:16 and twilight ends at 20:49. There's a total of 14 hours, 51 minutes of daylight today and 15 hours, 57 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:51 and sunrise is at 5:24. The moon is waxing crescent. Illumination was 5% at midnight, will be 7% at noon and 10% at midnight tonight. Moonrise was at 7:28 this morning. Moonset is at 22:37 tonight. Moonrise is at 8:24 tomorrow morning. Moonlight time is 15 hours, 9 minutes which is eight 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 five days.