April 15: ORD

Today is April 15th. It's the 106th day of the year. 260 days remain. It's week 16 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 59 and the normal low is 39. I've calculated the 33-year averages at 60 and 40.

On the warm side, in 2002 (O'Hare's warmest April 15th) the high was the record high of 88 with a low of 62. The former record high of 84 occurred at Midway in 1976. In 2003 the high was the record-challenging high of 86 with a low of 64. Two years ago, in 2010, the high was 82 with a low of 61. In 2004 the high was 75 with a low of 46. The other warm highs were 73 in 1982 and 72 in 2000. The record warmest low of 67 occurred in 1976 at Midway. 21 of the past 33 highs (64%) were in the: 50s (12) and 60s (9). O'Hare recorded six consecutive highs in the 50s & 60s from 1987 through 1992. On the warm side, six highs (18%) were in the: 70s (3) and 80s (3). O'Hare's warmest low of 65 degrees occurred on its third warmest April 15th in 1976. The high that day was 82 degrees. O'Hare also had a high of 79 in 1977 and six other highs in the 70s prior to 1979 (see next section). On the cold side, six highs (18%) were in the 40s.   

In looking back through the years to the first April at O'Hare in 1959, the following instances were notable: In 1977 the high was a warm 79 with a low of 49, a 30 degree spread and warm day. In 1976 the high was 82 with a low of 65, a warm day and year of the record warmest low of 67 at Midway. In 1973 the high was a warm 75 with a low of 44, a 31 degree spread. In 1971 the high was a warm 71 with a low of 35, a 36 degree spread. In 1969 the high was 61 with a warm low of 55, a six degree spread. In 1967 the high was 73 with a low of 54, a warm day. In 1964 the high was 62 with a low of 30, a 32 degree spread. In 1963 the high was a warm 73 with a low of 32, a 41 degree spread. In 1962 the high was a cold 42 with a low of 28, a cold day. In 1960 the high was a warm 72 with a low of 49, a warm day. In 1959 the high was a warm 71 with a low of 41, a 30 degree spread.

More recently, we had small spreads of five degrees in 1984 (42/37) and six degrees in 1993 (47/41). There were large spreads of 35 degrees in 1997 (66/31), 32 degrees in 1982 (73/41), 32 degrees in 2000 (72/40) and 30 degrees in 2005 (63/33).

On the cold side, in 1983 (O'Hare's coldest April 15th) the high was 40 with a low of 29. Three years later, in 1986, the high was 40 with a low of 31. These highs of 40 were the coldest highs for the date at O'Hare. The other cold highs were 42 in 1984, 45 in 1980, 45 in 1996 (our most recent 40s high) and 47 in 1993. O'Hare's other 20s low was 29 in 2007. The record low of 25 was set in 1943 at Midway. The record coldest high of 34 occurred back in 1928 at the University of Chicago. 28 of the last 33 lows (85%) were in the: 30s (16) and 40s (12). Two lows were in the cold 20s. O'Hare's second coldest April 15th was in 1962 as the high was 42 with a low of 28 (O'Hare's coldest low of the date). Three lows (of the last 33) were in the warm 60s. O'Hare's only lows in the 50s were 55 in 1969 and 54 in 1967.

Today is a major day in Chicago's snow history. 1961 was the year. O'Hare had 1.2 inches, the first of two days of 5.9 inches of snow. Midway had 1.1 inches, the first of three days of 6.8 inches of snow. Rockford didn't record any snow today, but stay tuned tomorrow!

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:43 and sunrise is at 6:12. Sunset is at 19:35 and twilight ends at 20:05. There's a total of 13 hours, 23 minutes of daylight today and 14 hours, 22 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:41 and sunrise is at 6:10. The moon is waning crescent, having reached last quarter two days ago at 5:50. Illumination was 32% at midnight, will be 27% at noon and 23% at midnight tonight. Moonrise was at 3:15 this morning. Moonset was at 14:25 this afternoon. Moonrise is at 3:44 tomorrow morning. Moonlight time is 11 hours, 10 minutes which is 33 minutes longer than yesterday. 

Spring began on March 12th and runs for 84 days through June 3rd. Warm Spring begins 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 usually occur infrequently. Earth Day is in seven days.