May 4: ORD

Today is May 4th. It's the 125th day of the year. 241 days remain. It's week 18 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 66 and the normal low is 45. I've calculated the 33-year averages at 66 and 44.

On the warm side, in 2000 (O'Hare's second warmest May 4th) the high was 81 with a low of 63. In 1981 the high was 78 with a low of 59. The year earlier, 1980, the high was 86 with a low of 49, a 37 degree spread. The other warm highs were 83 in 1982, 81 in 1999 and 79 two years ago, in 2010. The record high of 92 was set in 1952 and the record warmest low of 66 occurred three years later in 1955. Both records were set at Midway. 22 of the past 33 highs (67%) were in the: 50s (9) and 60s (13). O'Hare recorded consecutive 50s & 60s highs as follows: seven consecutive from 1991 through 1997 and eight consecutive from 2001 through 2008. On the warm side, ten highs (30%) were in the: 70s (6) and 80s (4). O'Hare's warmest May 4th was in 1960. The high was 90 with a low of 64, a hot day. Both the high and low were the warmest O'Hare has ever seen on the date. O'Hare's third warmest May 4th was in 1964 (high of 82, low of 60). The other 80s highs were 83 degrees in both 1962 and 1969. One high (3%) was in the cold 40s (49 in 1990). O'Hare coldest high was 43 in 1967. 

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 a cool 51 degrees. In 1976 the high was 68 with a low of 36, a 32 degree spread. In 1969 the high was a warm 83 with a low of 52, a 31 degree spread and warm day. In 1967 the high was 43 with a low of 33, a cold day. In 1966 the high was 62 with a cold low of 32, a 30 degree spread. In 1964 the high was 82 with a low of 60, a warm day. In 1962 the high was 83 with a low of 55, a warm day. In 1960 the high was a warm 80 degrees. In 1959 the high was 90 with a low of 64, a hot day.

More recently, we had additional large spreads of 35 degrees in 2002 (69/34), 32 degrees in 1982 (83/51) and 30 degrees in 1994 (66/36).
 
On the cool side, in 1992 the high was 54 with a low of 37. Two years earlier, in 1990, the high was 49 with a low of 43, a six degree spread. The other cool high was 54 in 1996. The post-1978 cold low was 33 in 2005. The record low of 32 was set in 1954 at Midway. The record coldest high of 41 occurred way back in 1907, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 30s (12) and 40s (14). O'Hare recorded ten consecutive 30s & 40s lows from 1983 through 1992. Seven lows (21%) were in the warm: 50s (6) and 60s (1). O'Hare's coldest May 4th was in 1967 (O'Hare's coldest high of the date of 43 with a low of 33). O'Hare's coldest low of the date was 32 in 1966.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:13 and sunrise is at 5:44. Sunset is at 19:57 and twilight ends at 20:28. There's a total of 14 hours, 13 minutes of daylight today and 15 hours, 15 minutes between twilights. We gained four minutes of daylight from yesterday. Tomorrow twilight begins at 5:12 and sunrise is at 5:43. The moon is waxing gibbous and will be full tomorrow night at 22:35. Illumination was 94% at midnight, will be 97% at noon and 99% at midnight tonight. Moonset was at 4:26 this morning. Moonrise is at 18:33 tonight. Moonset is at 5:05 tomorrow morning. Moonlight time is 9 hours, 53 minutes which is 42 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. Mother's Day is in nine days.