April 23: ORD

Today is April 23rd. It's the 114th day of the year. 252 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 62 and the normal low is 41. I've calculated the 33-year averages at 62 and 40.

On the warm side, in 1985 (O'Hare's second warmest April 23rd) the high was 77 with a low of 59. Five years later, in 1990, the high was 80 with a low of 49, a 31 degree spread. In 2008 the high was 74 with a low of 53. The other warm high was 75 in 1979. The record high of 88 and record warmest low of 66 were set on the same hot day in 1960 at Midway. 13 of the past 33 highs (40%) were in the 60s. 11 highs (33%) were in the: 40s (4) and 50s (7). Our most recent 50s high was 56 in 2003. On the warm side, nine highs (27%) were in the: 70s (8) and 80s (1). O'Hare's warmest April 23rd was in 1960 (high of 86, low of 66). That high of 86 was O'Hare's only other 80s high of the date and the low of 66 was O'Hare's only 60s low of the date. 

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1975 the high was a warm 74 degrees. In 1974 the high was a cold 44 with a low of 37, a seven degree spread. In 1971 the high was 68 with a low of 32, a 36 degree spread. In 1969 the high was a cold 49 degrees. In 1967 the high was 43 with a low of 26, a cold day. In 1963 the high was a cold 45 degrees. In 1960 the high was 86 with a low of 66, a hot day and year of the record high of 88 and record warmest low of 66, both at Midway.

More recently, we've an additional small spread of seven degrees in 1988 (47/40). The additional large spreads were: 38 degrees in 1986 (63/25), 34 degrees in 1994 (69/35), 33 degrees in 1979 (75/42), 32 degrees in 1998 (72/40), 31 degrees in 1980 (72/41), 31 degrees in 2006 (72/41), 30 degrees in 1982 (67/37) and 30 degrees in 2009 (67/37).
 
On the cold side, in 2005 (O'Hare's second coldest April 23rd) the high was 42 (our most recent 40s high) with a low of 35, a seven degree spread. In 1984 the high was 41 (O'Hare's coldest high of the date) with a low of 37, a four degree spread. The other cold low was the record low of 25 in 1986. The record low of 25 was originally set way back in 1873. The other cold highs were 47 in 1988, 48 in 1999 and 50 in 1995. The record coldest high of 35 was set way back in 1910, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the last 33 lows (88%) were in the: 30s (15) and 40s (14). One low was in the cold 20s (the record low) and three were in the warm 50s. O'Hare's coldest April 23rd was in 1967 (high of 43, low of 26). Another pre-1979 cold day was in 1974 (high of 44, low of 37).

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1984 the high was 41 with a low of 37, overall 13 degrees BELOW normal. Then in 1985 the high was 77 with a low of 59, overall 16 degrees ABOVE normal.  

Today is a major day in Chicago's snow history. In 1967, 3.4 inches fell at O'Hare. Midway had 3.1 inches and Rockford had 3.8 inches.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:30 and sunrise is at 5:59. Sunset is at 19:44 and twilight ends at 20:14. There's a total of 13 hours, 45 minutes of daylight today and 14 hours, 44 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 5:28 and sunrise is at 5:58. The moon is waxing crescent, having passed new two days ago at 2:18. Illumination was 3% at midnight, will be 5% at noon and 8% at midnight tonight. Moonrise was at 7:08 this morning. Moonset was at 22:17 tonight. Moonrise is at 7:51 tomorrow morning. Moonlight time is 15 hours, 9 minutes which is 18 minutes longer 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 in four days.