May 26: ORD

Today is May 26th. It's the 147th day of the year. 219 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 49.

On the warm side, two years ago, in 2010 (tied with 1967 as O'Hare's warmest May 26th), the high was 87 with a low of 66. In 1985 the high was 89 with a low of 62. In 1991 the high was 82 with a low of 69 (O'Hare's warmest low of the date). In 1987 the high was 86 with a low of 61. The record high of 94 was set back in 1911 and the record warmest low of 75 occurred 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 (9) and 70s (13). O'Hare recorded six consecutive highs in the 60s & 70s from 1979 through 1984. Six highs (18%) were in the warm 80s. Five highs (15%) were in the cool: 40s (1) and 50s (4). There seems to be a distinction in terms of the eras of the 80s highs. The first three happened between 1985 and 1991. The second three happened between 2006 and two years ago (2010). 1967 is tied with 2010 as the warmest May 26th with a high of 92 (O'Hare's warmest high of the date) and low of 61.

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 87 with a low of 65, a hot day. In 1971 the high was a cool 54 with a low of 43, a cool day. In 1969 the high was 74 with a cold low of 39, a 35 degree spread. In 1967 the high was a hot 92 with a low of 61, a 31 degree spread and hot day. In 1966 the high was 82 with a low of 49, a 33 degree spread. In 1965 the low was a warm 63 degrees. In 1962 the high was a cool 59 degrees. In 1961 the high was 47 with a low of 36, a cold day and year of the record coolest high. In 1959 the high was 84 with a warm low of 64, a warm day.

More recently, there were large spreads of 36 degrees in 1988 (78/42), 36 degrees in 2002 (73/37), 34 degrees in 2008 (81/47), 33 degrees in 1993 (78/45), 31 degrees in 1979 (70/39) and 31 degrees in 1998 (78/47).

On the cool side, in 1992 (O'Hare's second coolest May 26th) the high was 53 with a low of 35. Last year, in 2011, the high was 49 with a low of 43. This was only the second 40s high in O'Hare's history for the date (just 3.7% of the highs in its history and 2.8% in Chicago's history). In 1983 the high was 60 with the record low of 34. In 2001 the high was 57 with a low of 38. In 1994 the high was 59 with a low of 37. In 1997 the high was 55 with a low of 46. The other cool high was 60 in 1996. The other cold lows were 37 in 2002 and 39 in 1979. The record coolest high of 48 occurred in 1961. 22 of the last 33 lows (67%) were in the: 40s (14) and 50s (8). There were six consecutive 40s & 50s lows from 1995 through 2000. Five of the six (83%) were in the 40s. Six lows (18%) were in the cold 30s. Our most recent 30s low was 37 in 2002. Five lows (15%) were in the warm 60s. O'Hare's coldest May 26th was in 1961 as the high was 47 (O'Hare's coolest high of the date) with a low of 36. The other pre-1979 cold low was 39 in 1969.

There were two instances of back-to-back years in which temperatures were just about as opposite as they can be. In 1991 the high was 82 with a low of 69, overall 13.5 degrees ABOVE normal. Then in 1992 the high was 53 with a low of 35, overall 18 degrees BELOW normal. In the second instance, in 2010 the high was 87 with a low of 66, overall 14.5 degrees ABOVE normal. Then in 2011 the high was 49 with a low of 43, overall 16 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:49 and sunrise is at 5:23. Sunset is at 20:19 and twilight ends at 20:52. There's a total of 14 hours, 56 minutes of daylight today and 16 hours, 3 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:49 and sunrise is at 5:22. The moon is waxing crescent, heading towards the first quarter in two days at 15:16. Illumination was 24% at midnight, will be 29% at noon and 33% at midnight tonight. Moonrise was at 10:27 this morning. Moonset is at 0:23 tomorrow morning. Moonrise is at 11:31 tomorrow morning. Moonlight time is 13 hours, 33 minutes which is 54 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 two days.