April 27: ORD

Today is April 27th. It's the 118th day of the year. 248 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 64 and the normal low is 43. I've calculated the 33-year averages at 61 and 42.

On the warm side, in 1986 (O'Hare's second warmest April 27th) the high was the record high of 87 with a low of 61. Four years later, in 1990, the high was 84 with a low of 62. In 1984 the high was 80 with a low of 56. In 1991 the high was 71 with a low of 58. The other warm highs were 79 in 1981 and 75 in 2003. The record warmest low of 67 occurred back in 1915, at a time when the official readings were taken adjacent to Lake Michigan. 13 of the past 33 highs (40%) were in the 50s. 12 highs (36%) were in the: 60s (6) and 70s (6). Our most recent 60s high was 63 in 2001. There's a fight for the middle ground of sorts: 50s versus 60s & 70s. On the cold side, five highs (15%) were in the 40s. On the warm side, three highs (9%) were in the 80s. O'Hare's warmest April 27th was in 1962 as the high was 84 with O'Hare's warmest low of the date, 66 degrees. The other pre-1979 80s highs were 82 in 1974 and 81 in 1977.

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 66 with a low of 35, a 31 degree spread. In 1977 the high was a warm 81 with a low of 44, a 37 degree spread. In 1976 the high was a cold 49 with a low of 32, a cold day. In 1974 the high was 82 with a low of 55, a warm day. In 1971 the high was a cold 48 degrees. In 1970 the high was 77 with a low of 60, a warm day. In 1969 the low was a warm 55 degrees. In 1966 the high was a cold 43 with a low of 37, a six degree spread and cold day. In 1965 the high was 63 with a low of 32, a 31 degree spread. In 1964 the high was 63 with a warm low of 58, a five degree spread. In 1962 the high was 84 with a low of 66, a warm day. In 1959 the high was a cold 47 with a low of 40, a seven degree spread.

More recently, we had additional small spreads of five degrees in 1980 (45/40) and seven degrees in 1999 (53/46). We had large spreads of 40 degrees in 1981 (79/39), 39 degrees in 2003 (75/36), 33 degrees in 2006 (71/38), 32 degrees in 1993 (66/34), 32 degrees in 1994 (69/37) and 30 degrees in 2000 (68/38).

On the cold side, 1988 and 1992 are tied as O'Hare's coldest April 27th days. In 1988 the high was 42 (O'Hare's coldest high of the date) with a low of 36, a six degree spread. Four years later, in 1992, the high was 47 (our most recent 40s high) with a low of 31 (O'Hare's coldest low of the date). The other cold highs were 45 in 1980, 47 in 1979, 48 in 1985 and 51 two years ago, in 2010. The record low of 29 was set in 1945 at Midway. The record coldest high of 39 occurred in 1934 at the University of Chicago. 28 of the last 33 lows (85%) were in the: 30s (17) and 40s (11). O'Hare recorded 17 consecutive lows in the 30s & 40s from 1992 through 2008. O'Hare had lows of 32 degrees in 1965, 1976 and 1996. Five lows were in the warm: 50s (3) and 60s (2).

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1991 the high was 71 with a low of 58, overall 11.5 degrees ABOVE normal. Then in 1992 the high was 47 with a low of 31, overall 14 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:23 and sunrise is at 5:54. Sunset is at 19:49 and twilight ends at 20:19. There's a total of 13 hours, 55 minutes of daylight today and 14 hours, 56 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:22 and sunrise is at 5:52. The moon is waxing crescent, heading towards first quarter in two days at 4:57. Illumination was 29% at midnight, will be 34% at noon and 38% at midnight tonight. Moonset was at 0:38 this morning. Moonrise is at 10:30 this morning.  Moonset is at 1:15 tomorrow morning. Moonlight time is 14 hours, 8 minutes which is 20 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. Arbor Day is today. May Day is in four days. Mother's Day is in 16 days.