April 7: ORD

Today is April 7th. It's the 98th day of the year. 268 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 56 and the normal low is 36. I've calculated the 33-year averages at 54 and 34.

On the warm side, in 1991 (O'Hare's warmest April 7th) the high was 79 with a low of 60. A decade later, in 2001, the high was the near-record high of 83 with a low of 44, a 39 degree spread. In 1980 the high was 71 with a low of 47. In 1986 the high was 79 with a low of 39, a 40 degree spread. In 1981 the high was 74 with a low of 43, a 31 degree spread. The other warm high was 77 in 1999. The record high of 84 was set way back in 1893. The record warmest low of 62 occurred back in 1929. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 18 of the past 33 highs (55%) were in the: 40s (10) and 50s (8). On the warm side, 11 highs (33%) were in the: 60s (5), 70s (5) and 80s (1). Our most recent: 60s high was 63 in 2004 and 70s high was 77 in 1999. Prior to 1979, O'Hare's warmest April 7th was in 1959 with a high of 70 and low of 51. The other pre-1979 warm highs were 73 in 1978, 72 in 1968, 71 in 1969 and 68 in 1971. On the cold side, four highs (12%) 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 73 with a low of 45, a warm day. In 1975 the high was a cold 41 degrees. In 1972 the high was 33 with a low of 21, a cold day. In 1971 the high was a warm 68 with a low of 30, a 38 degree spread. In 1970 the high was 61 with a low of 30, a 31 degree spread. In 1969 the high was a warm 71 with a low of 38, a 33 degree spread. In 1968 the high was a warm 72 with a low of 40, a 32 degree spread. In 1966 the high was a cold 44 degrees. In 1959 the high was 70 with a low of 51, a warm day.

More recently, we had a small spread of seven degrees last year, in 2011 (46/39). We had large spreads of 44 degrees in 1999 (77/33) and 30 degrees in 1994 (51/21).

On the cold side, in 1982 the high was 34 with the record low of 7. In 2007 the high was the record coldest high of 32 with a low of 22. In 1996 the high was 39 with a low of 23. In 2003 the high was 34 with a low of 30, a four degree spread. In 1979 the high was 40 with a low of 24. In 1990 the high was 45 with a low of 22. In 1997 the high was 43 with a low of 26. The other cold low was 21 in 1994. The other cold high was 44 in 1983. 24 of the last 33 lows (73%) were in the: 20s (9) and 30s (15). O'Hare recorded consecutive lows in the 20s & 30s as follows: eight from 1983 through 1990 and six from 1992 through 1997. One low (3%) was in the cold single digits (1).  There have been no lows in the 10s (a.k.a. teens) in O'Hare's history on April 7th. 1972 (high of 33, low of 21) ties 2007 as O'Hare's second coldest April 7th. Eight of the last 33 lows (25%) were in the warm: 40s (7) and 60s (1). O'Hare's only 50s low was 51 in 1959.

1982 had the coldest temperatures. Area lows were: Rockford: 5, Barrington: 5, Chicago Botanical Gardens: 10, Midway: 10, Marengo: 6, Wheaton: 4, Aurora: 8 and Elgin: 11. In northwest Illinois, Mt. Carroll had a low of minus 2.

There were three instances of back-to-back years in which temperatures were just about as opposite as they can be. In the first instance, in 1979 the high was 40 with a low of 24, overall 14 degrees BELOW normal. Then in 1980 the high was 71 with a low of 47, overall 13 degrees ABOVE normal.  In the second instance, in 1981 the high was 74 with a low of 43, overall 12.5 degrees ABOVE normal. Then in 1982 the high was 34 with a low of 7, overall 25.5 degrees BELOW normal. In the third instance, in 1990 the high was 45 with a low of 22, overall 12.5 degrees BELOW normal. Then in 1991 the high was 79 with a low of 60, overall 23.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:56 and sunrise is at 6:25. Sunset is at 19:26 and twilight ends at 19:55. There's a total of 13 hours, 1 minute of daylight today and 13 hours, 59 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 5:55 and sunrise is at 6:23. The moon is waning gibbous, having reached the full Pink (a.k.a. Sprouting Grass/Egg/Fish) moon yesterday at 14:19. Illumination was 100% at midnight, will be 99% at noon and 97% at midnight tonight. Moonset is at 6:35 this morning. Moonrise is at 21:03 tonight. Moonset is at 7:17 tomorrow morning. Moonlight time is 9 hours, 32 minutes which is 41 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. Easter is tomorrow. Earth Day is in 15 days.