April 24: ORD

Today is April 24th. It's the 115th day of the year. 251 days remain. It's week 17 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 63 and the normal low is 42. I've calculated the 33-year averages at 64 and 42.

On the warm side, in 1990 (O'Hare's warmest April 24th) the high was the record high of 87 with a low of 66. Four years later, in 1994, the high was 83 with a low of 54. Three years ago, in 2009, the high was 84 with a low of 49, a 35 degree spread. In 1986 the high was 81 with a low of 47, a 34 degree spread. In 1993 the high was 76 with a low of 52. In 2008 the high was 74 with a low of 54. The other warm high was 75 in 1998. The other warm low was 55 in 1979. The record warmest low of 68 was set in 1915. The record high of 87 originally occurred in 1915, making 1915 the overall warmest day. In 1915 the official observations were taken adjacent to Lake Michigan. 27 of the past 33 highs were in the: 50s (10), 60s (10) and 70s (7). On the warm side, four highs were in the 80s. O'Hare's second warmest April 24th was in 1960 (high of 85, low of 65 (one of just two 60s lows of the date)). On the cold side, two highs were in the 40s.

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1972 the high was a cold 45 with a low of 34, a cold day. In 1971 the low was a cold 30 degrees. In 1968 the high was a cold 41 with a low of 36, a five degree spread and cold day. In 1967 the high was 40 with a low of 25, a cold day. In 1965 the high was a cold 45 with a low of 40, a five degree spread. In 1964 the high was a cold 50 degrees. In 1962 the high was a warm 78 with a low of 44, a 34 degree spread. In 1961 the high was a warm 76 with a low of 40, a 36 degree spread. In 1960 the high was 85 with a low of 65, a hot day.

More recently, we had additional large spreads of 34 degrees in 2006 (73/39), 32 degrees in 1996 (68/36), 31 degrees in 2002 (73/42) and 30 degrees in 1995 (62/32). There were no small spreads of seven degrees or less.
 
On the cold side, in 1980 (O'Hare's second coldest April 24th) the high was 44 with a low of 32. Three years later, in 1983, the high was 54 with a low of 32. The other cold highs were 48 in 1992, 50 in 2004, 51 in 1981 and 51 in 1984. The record low of 29 was set way back in 1910. The record coldest high of 36 was set way back in 1892. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 27 of the last 33 lows (82%) were in the: 30s (14) and 40s (13). Six lows were in the warm: 50s (5) and 60s (1). O'Hare's coldest April 24th was in 1967 as the high was 40 (the coldest high of the date) with a low of 25 (the only 20s low and coldest low of the date). The other notable pre-1979 cold April 24ths were 1968 (41/36) and 1972 (45/34). 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:28 and sunrise is at 5:58. Sunset is at 19:45 and twilight ends at 20:15. There's a total of 13 hours, 47 minutes of daylight today and 14 hours, 47 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:27 and sunrise is at 5:57. The moon is waxing crescent. Illumination was 8% at midnight, will be 10% at noon and 13% at midnight tonight. Moonrise was at 7:51 this morning. Moonset was at 23:08 tonight. Moonrise is at 8:39 tomorrow morning. Moonlight time is 15 hours, 17 minutes which is eight minutes longer than yesterday. Moonlight time is at a peak today. 

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. Arbor Day is in three days.