April 6: ORD

Today is April 6th. It's the 97th day of the year. 269 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 55 and the normal low is 36. I've calculated the 33-year averages at 55 and 35.

On the warm side, in 1991 (O'Hare's warmest April 6th) the high was 83 with a low of 58 (the only warm low of the date). In 2005, the high was 80 with a low of 45, a 35 degree spread. These were O'Hare's only 80s highs of the date. Two years ago, in 2010, the high was 76 with a low of 47. The other warm highs were 72 in 2004 and 67 in 1995. The record high of 84 and record warmest low of 69 were set on the same warm day back in 1929, at a time when the official readings were taken adjacent to Lake Michigan. 19 of the past 33 highs (58%) were in the: 50s (9) and 60s (10). On the warm side, four highs (12%) were in the: 70s (2) and 80s (2). O'Hare's pre-1979 warm highs were 72 in 1963, 71 in 1965, 70 in 1964 and 67 in 1973. On the cold side, ten highs (30%) were in the: 30s (6) and 40s (4). 

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1977 the low was a cold 24 degrees. In 1975 the high was a cold 38 degrees. In 1973 the high was a warm 67 degrees. In 1972 the high was 65 with a low of 33, a 32 degree spread. In 1967 the high was 49 with a low of 42, a seven degree spread. In 1966 the high was a cold 40 with a low of 35, a five degree spread. In 1965 the high was a warm 71 with a low of 42, a warm day. In 1964 the high was a warm 70 with a low of 45, another warm day. In 1963 the high was a warm 72 with a low of 37, a 35 degree spread. In 1961 the high was a cold 43 with a low of 36, a seven degree spread.

More recently, we had a small spread of seven degrees in 2003 (37/30). There were large spreads of 34 degrees in 1981 (56/22), 33 degrees in 1992 (66/33) and 31 degrees in 1995 (67/36).

On the cold side, in 1982 (O'Hare's coldest April 6th) the high was the record coldest high of 32 with the record low of 15. Three years earlier, in 1979, the high was 36 with a low of 19. Those were the only 10s (a.k.a. teens) lows of the date. In 2007 the high was 36 with a low of 23. In 1994 the high was 36 with a low of 26. Four years before, in 1990, the high was 38 with a low of 24. In 1996 the high was 40 with a low of 25. In 2003 the high was 37 with a low of 30. The other cold lows were 22 in 1981 and 24 in 2002. The other cold high was 40 three years ago in 2009. 23 of the last 33 lows (70%) were in the: 30s (14) and 40s (9). O'Hare recorded seven consecutive 30s & 40s lows from 1983 through 1989, five of which (71%) were in the 30s. Nine lows (27%) were in the cold: 10s (a.k.a. teens) (2) and 20s (7). One low (3%) was in the warm 50s.

1982 and 1979 had some very cold low temperatures. In 1982, the lows were: Rockford: 11, Barrington: 13, Chicago Botanical Gardens: 17, University of Chicago: 18, Midway: 16, Elgin: 12, Marengo: 11 and Wheaton: 14. In 1979, lows were: Midway: 16, Barrington: 18, Elgin: 15, Marengo: 18, Rockford: 13, DeKalb: 23, Wheaton: 18 and Aurora: 19.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1990 the high was 38 with a low of 24, overall 14 degrees BELOW normal. Then in 1991 the high was 83 with a low of 58, overall 25.5 degrees ABOVE normal. 

Today is a major day in Chicago's snow history. In 1982, Midway had 0.7 inches, the final part of a total of 10.5 inches. In 1938, the city recorded nine (9") inches of snow.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:58 and sunrise is at 6:27. Sunset is at 19:25 and twilight ends at 19:54. There's a total of 12 hours, 58 minutes of daylight today and 13 hours, 56 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:56 and sunrise is at 6:25. The moon reaches the full Pink (a.k.a. Sprouting Grass/Egg/Fish) moon today at 14:19. Illumination was 99% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset is at 5:58 this morning. Moonrise is at 19:25 tonight. Moonset is at 6:35 tomorrow morning. Moonlight time is 10 hours, 13 minutes which is 43 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. Good Friday is today. Easter is in two days. Earth Day is in 16 days.