April 5: ORD

Today is April 5th. It's the 96th day of the year. 270 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 35. I've calculated the 33-year averages at 54 and 33.

On the warm side, in 1988 (O'Hare's warmest April 5th) the high was the record high of 85 (and only 80s high of the date) with a low of 54, a 31 degree spread. Two years earlier, in 1986, the high was 76 with a low of 49. In 2005 the high was 76 with a low of 47. In 1997 the high was 67 with a low of 55 (O'Hare's warmest low of the date). Two years ago, in 2010, the high was 72 with a low of 50. In 1991 the high was 76 with a low of 45, a 31 degree spread. The record warmest low of 69 occurred back in 1929, at a time when the official readings were taken adjacent to Lake Michigan. 24 of the past 33 highs (73%) were in the: 40s (9), 50s (9) and 60s (6). O'Hare recorded six consecutive 40s, 50s and 60s highs from 1997 through 2002. Prior to 1979, O'Hare's only warm high was 67 in 1967. On the warm side, five highs (15%) were in the: 70s (4) and 80s (1). On the cold side, four highs (12%) were in the 30s. Our most recent 30s high was 33 in 2003.  

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1976 the high was 62 with a low of 31, a 31 degree spread. In 1975 the high was 35 with a low of 18, a cold day. In 1968 the high was a cold 43 degrees. In 1967 the high was 67 with a low of 49, a warm day. In 1966 the high was a cold 43 degrees. In 1963 the high was 62 with a low of 29, a 33 degree spread. In 1960 the high was a cold 42 degrees.

More recently, we had small spreads of six degrees in both 1983 (41/35) and 1985 (39/33). There were additional large spreads of 38 degrees in 2000 (63/25) and 36 degrees in 1979 (55/19).
 
On the cold side, in 1982 (tied with 1975 as O'Hare's coldest April 5th) the high was the record coldest high of 31 with a low of 22. In 2003 the high was 33 with a low of 25. In 1996 the high was 39 with a low of 25. In 2002 the high was 41 with a low of 24. Five years later, in 2007, the high was 40 with a low of 27. In 1995 the high was 49 with the record low of 18 (the low ties 1975 as coldest of the date), a 31 degree spread. The record low of 18 was first set in 1979 at Midway. The other cold low was 19 in 1979. The other cold highs were 39 in 1985, 41 in 1983, 42 in 1981 and 43 three years ago in 2009. The former record coldest high of 32 occurred way back in 1898. 24 of the last 33 lows (73%) were in the: 20s (11) and 30s (13). O'Hare recorded six consecutive 20s & 30s lows from 1980 through 1985. Two lows (6%) were in the cold 10s (a.k.a. teens). 1975 (high of 35, low of 18) is tied with 1982 as O'Hare's coldest April 5th. Seven lows (21%) were in the warm: 40s (4) and 50s (3). Our most recent 40s low was 47 in 2005.

Both 1979 and 1995 had comparable cold lows today. In 1979, area lows were: Rockford: 17, Aurora: 17, Barrington: 9, University of Chicago: 18, DeKalb (NIU): 18, Elgin: 11, Marengo: 8, Joliet: 18, Wheaton: 16, Midway: 18 and O'Hare: 19. In 1995, area lows were: Rockford: 15, Aurora: 19, Chicago Botanical Gardens: 16, Midway: 23, DeKalb(NIU): 17, Elgin: 16, Lake Villa: 16, Marengo: 15, O'Hare: 18 and Streamwood: 12.  

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1996 the high was 39 with a low of 25, overall 13 degrees BELOW normal. Then in 1997 the high was 67 with a low of 55, overall 16 degrees ABOVE normal. 

Today is a major day in Chicago's snow history. In 1982, O'Hare had 9.4 inches of snow. This was 89% of it's total of 10.6 inches for the month. Midway had 9.8 inches and Rockford had 6.3 inches. So much for Spring on this day in 1982! In 1938, the city had a tenth of an inch.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:00 and sunrise is at 6:28. Sunset is at 19:24 and twilight ends at 19:53. There's a total of 12 hours, 56 minutes of daylight today and 13 hours, 53 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 5:58 and sunrise is at 6:27. The moon is waxing gibbous and will reach the full Pink (a.k.a. Sprouting Grass/Egg/Fish) moon tomorrow at 14:19. Illumination was 96% at midnight, will be 98% at noon and 99% at midnight tonight. Moonset is at 5:25 this morning. Moonrise is at 18:29 tonight. Moonset is at 5:58 tomorrow morning. Moonlight time is 10 hours, 56 minutes which is 44 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 tomorrow. Easter is in three days.