April 30: ORD

Today is April 30th. It's the 121st day of the year. 245 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 65 and the normal low is 44. I've calculated the 33-year averages at 63 and 43.

On the warm side, two years ago, in 2010 (O'Hare's warmest April 30th), the high was 81 with a low of 62. In 2001 (O'Hare's third warmest April 30th) the high was 85 (O'Hare's warmest high of the date) with a low of 50, a 35 degree spread. The other warm low was 57 in 1986. The record high of 91 and record warmest low of 68 were set on the same hot day in 1942 at the University of Chicago. 26 of the past 33 highs (79%) were in the: 50s (10) and 60s (16). O'Hare recorded consecutive highs in the 50s & 60s as follows: eight from 1986 through 1993 (of which, seven of them, or 88% were 60s) and eight from 2002 through 2009. On the warm side, five highs (15%) were in the: 70s (3) and 80s (2). O'Hare's second warmest April 30th was in 1970 as the high was 71 with a low of 66 (O'Hare's warmest low of the date). O'Hare's fourth warmest April 30th was in 1962 as the high was 84 with a low of 49. That high of 84 was the warmest for many years, having been eclipsed in 2001. On the cold side, two highs (6%) 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 1978 the high was a cold 48 with a low of 35, a cold day. In 1977 the high was 71 with a low of 39, a 32 degree spread. In 1970 the high was 71 with a warm low of 66, a five degree spread and warm day. In 1968 the high was 72 with a low of 42, a 30 degree spread. In 1964 the high was a cold 49 with a low of 45, a four degree spread. In 1963 the high was a cold 51 with a low of 34, a cold day. In 1962 the high was a warm 84 with a low of 49, a 35 degree spread and warm day. In 1961 the high was 67 with a low of 36, a 31 degree spread.

More recently, we had a small spread of seven degrees in 2006 (59/52). The additional large spreads were 35 degrees in 1985 (75/40), 34 degrees in 2000 (71/37) and 31 degrees in 1988 (69/38).

On the cold side, in 1994 (O'Hare's coldest April 30th) the high was 43 (O'Hare's coldest high of the date) with a low of 34. In 1979 the high was 47 with a low of 35. The other cool highs were 50 in 1995, 52 a year later in 1996 and 53 in 1987. The record low of 30 was set way back in 1873. In 2008 the low was a near-record 31 degrees (O'Hare's coldest low of the date). O'Hare had another cold low of 32 degrees in 1969. The record coldest high of 39 occurred way back in 1907. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 30s (12) and 40s (13). O'Hare recorded consecutive 30s & 40s lows as follows: ten from 1976 through 1985 and six from 1992 through 1997. Eight lows (24%) were in the warm: 50s (7) and 60s (1). O'Hare's only 60s lows of the date were 66 in 1970 and 62 in 2010.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:19 and sunrise is at 5:49. Sunset is at 19:52 and twilight ends at 20:23. There's a total of 14 hours, 3 minutes of daylight today and 15 hours, 4 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 5:18 and sunrise is at 5:48. The moon is waxing gibbous, having reached first quarter yesterday at 4:57. Illumination was 59% at midnight, will be 64% at noon and 69% at midnight tonight. Moonset is at 2:21 this morning. Moonrise is at 13:42 this afternoon.  Moonset is at 2:51 tomorrow morning. Moonlight time is 12 hours, 39 minutes which is 35 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. May Day is tomorrow. Mother's Day is in 13 days.