April 25: ORD

Today is April 25th. It's the 116th day of the year. 250 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 25th) the high was the record high of 87 with a low of 66. You may be seeing double! The high and low temperatures in 1990 were the same for the 24th and the 25th. Four years later, in 1994 (O'Hare's second warmest April 25th), the high was 85 with a low of 59. In 1979 the high was 73 with a low of 61. 1990 and 1979 boast the only 60s lows of the date. In 1986 the high was 75 with a low of 56. The other warm highs were 82 in 2008 and 77 three years ago, in 2009. The other warm low was 54 in 1996. The record warmest low of 68 occurred back in 1915, at a time when the official readings were taken adjacent to Lake Michigan. 20 of the past 33 highs (61%) were in the: 60s (12) and 70s (8). O'Hare recorded eight consecutive highs in the 60s & 70s from 1982 through 1989. Also, there were six consecutive 60s highs from 1996 through 2001. On the warm side, three highs (9%) were in the 80s. O'Hare's third warmest April 25th was in 1962 (high of 84, low of 56). 1962 was also the year of the former record high of 86, set at Midway. On the cold side, ten highs (30%) were in the: 40s (4) and 50s (6). O'Hare's coldest highs of the date were 45 degrees in 1961 and 1976. 

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1976 the high was a cold 45 with a low of 36, a cold day. In 1974 the high was 66 with a low of 36, a 30 degree spread. In 1972 the high was a cold 50 with a low of 31, a cold day. In 1971 the high was 68 with a low of 37, a 31 degree spread. In 1970 the high was 76 with a low of 54, a warm day. In 1969 the high was 72 with a low of 41, a 31 degree spread. In 1967 the high was 52 with a cold low of 28, a cold day. In 1966 the high was 73 with a low of 39, a 34 degree spread. In 1962 the high was 84 with a low of 56, a warm day. 1962 is also the year of the former record high of 86 at Midway. In 1961 the high was a cold 45 with a low of 40, a five degree spread.

More recently, we had a small spread of four degrees in 2007 (49/45). We had large spreads of 43 degrees in 1983 (71/28), 38 degrees in 2008 (82/44), 36 degrees in 2009 (77/41), 32 degrees in 1988 (70/38), 31 degrees in 1984 (70/39), 30 degrees in 1985 (71/41) and 30 degrees in 1999 (63/33).

On the cold side, in 1980 the high was 46 with a low of 30. In 2006 the high was 46 with a low of 32. The other cold low was 28 in 1983. The other cold highs were 47 in 1992 and 49 in 2007. That low of 28 in 1983 was the low point of a day which saw a high of 71. The record low of 27 was set way back in 1887. The record coldest high of 40 occurred back in 1910. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 30s (13) and 40s (13). O'Hare recorded 15 consecutive lows in the 30s & 40s from 1997 through last year, 2011. One low (3%) was in the cold 20s. Besides the low of 28 in 1983, O'Hare's only other 20s low of the date was 28 in 1967. Six lows (18%) were in the warm: 50s (4) and 60s (2). Our most recent 50s low was 54 in 1996.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1979 the high was 73 with a low of 61, overall 15 degrees ABOVE normal. Then in 1980 the high was 46 with a low of 30, overall 14 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:27 and sunrise is at 5:57. Sunset is at 19:47 and twilight ends at 20:17. There's a total of 13 hours, 50 minutes of daylight today and 14 hours, 50 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 5:25 and sunrise is at 5:55. The moon is waxing crescent. Illumination was 13% at midnight, will be 17% at noon and 21% at midnight tonight. Moonrise was at 8:39 this morning. Moonset was at 23:55 tonight. Moonrise is at 9:32 tomorrow morning. Moonlight time is 15 hours, 16 minutes which is one minute shorter 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 two days.