May 10: ORD

Today is May 10th. It's the 131st day of the year. 235 days remain. It's week 19 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 68 and the normal low is 47. I've calculated the 33-year averages at 72 and 48.

On the warm side, in 1979 (O'Hare's warmest May 10th) the high was 90 with a low of 67 (O'Hare' warmest low of the date). Last year, in 2011, the high was the record high of 90 with a low of 62. Although it also hit 90 in 1979, O'Hare was not the official station of record in 1979. So prior to 2011, the record high was 89 in 1896. In 1987 the high was 88 with a low of 61. In 1993 the high was 87 with a low of 62. In 2005 the high was 82 with a low of 60. A year earlier, in 2004, the high was 84 with a low of 56. In 2007 the temperatures repeated, as the high was 84 with a low of 56. In 1982 the high was 86 with a low of 53, a 33 degree spread. In 2001 the high was 81 with a low of 58. The other warm highs were 83 in 1992 and 82 in 1985. The record warmest low of 69 was set way back in 1896, part of that scorching former record-high day. 27 of the past 33 highs (82%) were in the: 60s (10), 70s (8) and 80s (9). On the warm side, two highs were in the 90s. On the cool side, four highs were in the: 30s (1) and 50s (3). There have been no highs in the 40s in O'Hare's history for the date.

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 72 with a low of 41, a 31 degree spread. In 1977 the high was 62 with a cold low of 31, a 31 degree spread. In 1975 the high was 75 with a low of 45, a 30 degree spread. In 1972 the high was 67 with a cold low of 35, a 32 degree spread. In 1971 the high was 73 with a low of 42, a 31 degree spread. In 1969 the high was a cool 53 degrees. In 1966 the high was 52 with a low of 24, a cold day. In 1963 the high was a cool 56 degrees. In 1962 the high was a cool 52 degrees. In 1961 the low was a cold 35 degrees. In 1960 the high was a cold 39 with a low of 37, a small two degree spread and cold day. That high of 39 ties the record coldest high, but unofficially. In 1959 the high was 82 with a low of 61, a warm day.

More recently, we had an additional small spread of five degrees in 1995 (54/49). The additional large spreads were 42 degrees in 1983 (70/28), 37 degrees in 1992 (83/46), 32 degrees in 1999 (74/42), 31 degrees in 1984 (68/37) and 30 degrees in 1985 (82/52).
 
On the cool side, in 1981 (O'Hare's coldest May 10th) the high was the record coldest high of 39 with a low of 35, a four degree spread. In 1990 the high was 50 with a low of 36. The other cold low was the record low of 28 set in 1983. The other cool high was 54 in 1995. 21 of the last 33 lows (64%) were in the: 40s (13) and 50s (8). O'Hare recorded eight consecutive 40s & 50s lows from 1997 through 2004. Seven lows (21%) were in the cold: 20s (1) and 30s (6). Five lows (15%) were in the warm 60s. O'Hare also had a cold high of 39 degrees in 1960 (ties the record coldest high set in 1981). O'Hare also had a cold low of 24 in 1966 which is colder than the record low. 

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1981 the high was 39 with a low of 35, overall 20 degrees BELOW normal. Then in 1982 the high was 86 with a low of 53, overall 12.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:05 and sunrise is at 5:37. Sunset is at 20:03 and twilight ends at 20:35. There's a total of 14 hours, 26 minutes of daylight today and 15 hours, 30 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:04 and sunrise is at 5:36. The moon is waning gibbous, heading towards last quarter in two days at 16:47. Illumination was 77% at midnight, will be 73% at noon and 67% at midnight tonight. Moonrise was at 0:02 this morning. Moonset is at 10:02 this morning. Moonrise is at 0:42 tomorrow morning.  Moonlight time is 10 hours which is an hour and 7 minutes longer than yesterday.