May 25: ORD

Today is May 25th. It's the 146th day of the year. 220 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 69 and 49.

On the warm side, two years ago, in 2010 (O'Hare's warmest May 25th), the high was 88 with a low of 69 (O'Hare's warmest low of the date). Four years earlier, in 2006, the high was 75 with a low of 64. The other warm high was 84 in 1985. The record high of 94 was set back in 1911 and the record warmest low of 72 occurred back in 1914. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 22 of the past 33 highs (67%) were in the: 60s (12) and 70s (10). O'Hare recorded seven consecutive 60s & 70s highs from 2003 through 2009. Four highs (12%) were in the warm 80s. Seven highs (21%) were in the cool 50s. Our most recent 50s highs were 59 in 2001 and 57 in 2002. O'Hare's second warmest May 25th was in 1977 as the high was 90 (O'Hare's warmest high of the date) with a low of 62. The third warmest was in 1965 (high of 82, low of 67).

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 82 with a low of 52, a 30 degree spread. In 1977 the high was a hot 90 with a low of 62, a hot day. In 1975 the low was a warm 66 degrees. In 1972 the high was a warm 85 degrees. In 1971 the high was a cool 60 degrees. In 1967 the high was 84 with a low of 49, a 35 degree spread. In 1965 the high was 82 with a warm low of 67, a warm day. In 1964 the high was 80 with a low of 48, a 32 degree spread. In 1961 the low was a cold 39 degrees.

More recently, there was a small spread of seven degrees in 1990 (60/53). There were large spreads of 34 degrees in 1985 (84/50), 34 degrees in 2008 (78/44), 31 degrees in 1981 (80/49) and 30 degrees in 1980 (82/52).
 
On the cool side, in 1992 (O'Hare's coolest May 25th) the high was 51 (O'Hare's coolest high of the date) with the record low of 32. In 1988 the high was 59 with a low of 37. Five years prior, in 1983, the high was 59 with a low of 38. In 2002 the high was 57 with a low of 41. In 1997 the high was 54 with a low of 45. In 1996 the high was 56 with a low of 45. The other cool highs were 59 in 2001 and 60 in 1990. The record coolest high of 44 occurred way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 28 of the last 33 lows (85%) were in the: 40s (14) and 50s (14). Three lows were in the cold 30s and two were in the warm 60s. The 30s lows occurred between 1983 and 1992 while the 60s lows occurred between 2006 and 2010. O'Hare's only 30s low prior to 1983 was 39 degrees in 1961.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:50 and sunrise is at 5:23. Sunset is at 20:18 and twilight ends at 20:51. There's a total of 14 hours, 55 minutes of daylight today and 16 hours, 1 minute between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:49 and sunrise is at 5:23. The moon is waxing crescent. Illumination was 16% at midnight, will be 20% at noon and 24% at midnight tonight. Moonrise was at 9:24 this morning. Moonset is at 23:51 tonight. Moonrise is at 10:27 tomorrow morning. Moonlight time is 14 hours, 27 minutes which is 25 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 three days.