April 29: ORD

Today is April 29th. It's the 120th day of the year. 246 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 64 and the normal low is 43. I've calculated the 33-year averages at 64 and 43.

On the warm side, in 2004 (O'Hare's second warmest April 29th) the high was 78 with a low of 59. In 1987 the high was 83 with a low of 45, a 38 degree spread. The other warm highs were 82 in 2007 and 79 two years ago, in 2010.  The record-tying high of 88 and record warmest low of 68 were set on the same hot day at Midway in 1970. The co-record high of 88 was first set way back in 1899. 28 of the past 33 highs (85%) were in the: 50s (8), 60s (12) and 70s (8). On the warm side, two highs were in the 80s. O'Hare's warmest April 29th was in 1970 as the high was 86 (O'Hare's warmest high of the date) with a low of 69 (O'Hare's warmest low of the date). The only other 60s low was 60 in 1974. On the cold side, three highs were in the 40s. We've seen all five categories of highs the past five years: 62 last year, 79 in 2010, 55 in 2009, 44 in 2008 and 82 in 2007.

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 70 with a low of 40, a 30 degree spread. In 1977 the high was 64 with a cold low of 30, a 34 degree spread. That low of 30 was lower than the record low. In 1975 the high was a warm 76 with a low of 39, a 37 degree spread. In 1974 the low was a warm 60 degrees. In 1971 the high was a cold 51degrees. In 1970 the high was 86 with a low of 69, a hot day (the day of the record high of 88 and record warmest low of 68 at Midway). In 1969 the high was a cold 51 with a low of 33, a cold day. In 1966 the high was 67 with a low of 36, a 31 degree spread. In 1965 the high was 70 with a low of 35, a 35 degree spread. In 1961 the low was a cold 30 degrees (lower than the record low).

More recently, we had additional large spreads of 37 degrees in 2007 (82/45), 33 degrees in 1985 (69/36), 33 degrees two years ago, in 2010 (79/46), 32 degrees in 1988 (65/33) and 31 degrees in 1986 (74/43). There have been no small spreads of up to seven degrees in O'Hare's history on April 29th.

On the cold side, in 2008 (O'Hare's coldest April 29th) the high was 44 (O'Hare's coldest high of the date) with the record-tying low of 31. In 1996 the high was 45 with a low of 36. In 1979 the high was 48 with a low of 37. The co-record low of 31 occurred in 1958 at Midway. O'Hare had lows of 30 degrees in both 1977 and 1961 but in these years O'Hare was not the official station of record for Chicago. The record coldest high of 39 was set way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 21 of the last 33 lows (64%) were in the 40s. O'Hare recorded seven consecutive 40s lows from 1997 through 2003. Nine lows (27%) were in the cold 30s. Three lows (9%) were in the warm 50s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:20 and sunrise is at 5:51. Sunset is at 19:51 and twilight ends at 20:22. There's a total of 14 hours of daylight today and 15 hours, 2 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:19 and sunrise is at 5:49. The moon is reaches first quarter today at 4:57. Illumination was 48% at midnight, will be 54% at noon and 59% at midnight tonight. Moonset is at 1:50 this morning. Moonrise is at 12:36 this afternoon.  Moonset is at 2:21 tomorrow morning. Moonlight time is 13 hours, 14 minutes which is 29 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 in two days. Mother's Day is in 14 days.