April 1: ORD

Today is April 1st. It's the 92nd day of the year. 274 days remain. It's week 14 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. 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 53 and the normal low is 34. I've calculated the 33-year averages at 53 and 35.

On the warm side, two years ago, in 2010, the high was the new record high of 83 with the record-tying warmest low of 54. The co-record warmest low of 54 occurred in 1963 at Midway. In 2003 the high was 81 with a low of 39, a 42 degree spread. That high of 81 is just a degree short of the former record high of 82 which occurred in 1946. In 1999 the high was 62 with a low of 53. That low of 53 was just a degree short of the record warmest low. The other warm highs were 67 in both 1986 and 1994. The other warm lows were 46 in 2007 and 47 in 2000. 28 of the past 33 highs (85%) were in the: 40s (11), 50s (11) and 60s (6). On the warm side, two highs were in the 80s. O'Hare's second warmest April 1st was in 1963 as the high was 77 with a low of 54. The other pre-1979 warm highs were 71 in 1974 (O'Hare's most recent 70s high of the date) and 67 in 1978. On the cold side, three highs were in the 30s.

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 warm 67 with a low of 32, a 35 degree spread. In 1976 the high was 43 with a low of 37, a six degree spread. In 1974 the high was a warm 71 with a low of 41, a 30 degree spread and warm day. In 1972 the high was a cold 38 degrees. In 1970 the high was a cold 36 with a low of 34, a two degree spread. In 1969 the high was 64 with a low of 33, a 31 degree spread. In 1967 the low was a warm 47 degrees. In 1964 the low was a cold 19 degrees. In 1963 the high was 77 with a low of 54, a warm day and year of the co-record warmest low of 54 at Midway. In 1962 the high was a cold 40 degrees. In 1961 the high was 37 with a low of 22, a cold day. In 1959 the high was 42 with a low of 38, a four degree spread.

More recently, we had a small spread of five degrees in 1979 (39/34). There were large spreads of 35 degrees in 1997 (62/27), 31 degrees in 1984 (55/24), 30 degrees in 1986 (67/37) and 30 degrees in 1994 (67/37).
 
On the cold side, in 1993 the high was 35 with a low of 27. The year prior, in 1992, the high was 39 with a low of 28. The other cold highs were 39 in 1979, 41 in 1985 and 41 in 2002. The record low of 17 and record coldest high of 26 were set on the same cold day way back in 1881, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 20s (9) and 30s (17). 1961 was O'Hare's coldest April 1st as the high was 37 with a low of 22. O'Hare's coldest reading of the date was in 1964 when the low was 19. Seven lows (21%) were in the warm: 40s (5) and 50s (2).

Today is a major day in Chicago's snow history. 1970 was the first day of a two day storm. At O'Hare, 3.2 inches of a 7.2 inch total occurred. At Midway, 8.2 inches of a 10.7 inch total occurred. And in Rockford, 3.9 inches of a 6.7 inch total occurred.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:07 and sunrise is at 6:35. Sunset is at 19:20 and twilight ends at 19:48. There's a total of 12 hours, 45 minutes of daylight today and 13 hours, 41 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:05 and sunrise is at 6:33. The moon is waxing gibbous, having reached first quarter two days ago at 14:41. Illumination was 64% at midnight, will be 69% at noon and 74% at midnight tonight. Moonset was at 3:18 this morning. Moonrise is at 13:44 this afternoon. Moonset is at 3:52 tomorrow morning. Moonlight time is 13 hours, 34 minutes which is 26 minutes shorter than yesterday.

Spring began on March 12th and runs for 84 days through June 3rd. Cool Spring began on March 12th and runs for 32 days through April 12th. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 60s and 70s usually occur infrequently. April Fools' Day and Palm Sunday are today. Good Friday is in five days. Easter is in seven days.