May 21: ORD

Today is May 21st. It's the 141st day of the year. 224 days remain. It's week 21 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.

According to the National Climatic Data Center (NCDC), the normal high is 71 and the normal low is 50. I've calculated the 32-year averages at 72 and 48.

On the warm side, in 1987 the high was 89 with a low of 59, a 30 degree spread. Two years ago, in 2009, the high was 84 with a low of 60. Other warm highs were 87 in 1994, 86 in 1992 and 84 in 1991. The record high of 92 was set in 1977. The record warmest low of 71 occurred in 1921. 27 of the last 32 highs (84%) were in the: 60s (7), 70s (12) and 80s (8). Five highs were in the cool 50s. If we group the past three years and the three years before into a group, we find all three categories of highs (which comprise the 84%) represented. From 2005-7, highs were 73, 61 and 80. From 2008-10, highs were 66, 84 and 73. Going further back, the high was 77 in 2004. In 2002 and 2003, we had back-to-back highs in the 50s (58 & 57).

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1978 the high was a cool 57 with a low of 41, a cool day. In 1977 the high was 91 with a low of 67, a hot day and year of the record high of 92 at Midway. In 1975 the high was 79 with a warm low of 66, a warm day. In 1974 the high was 84 with a low of 66, a warm day. In 1972 the high was a warm 84 degrees. In 1970 the high was 86 with a low of 66, a hot day. In 1969 the high was a cool 57 with a low of 42, a cool day. In 1965 the high was a warm 83 with a low of 50, a 33 degree spread. In 1964 the high was 81 with a low of 39, a large 42 degree spread. In 1963 the high was a cool 58 degrees. In 1962 the high was a cool 56 degrees. In 1961 the high was 58 with a low of 36, a cool day. In 1959 the high was 86 with a low of 64, a hot day.

More recently, we had large spreads of 37 degrees in 1980 (82/45), 36 degrees in 1994 (87/51), 36 degrees in 2007 (80/44), 32 degrees in 1981 (79/47), 30 degrees in 1989 (80/50), 30 degrees in 1991 (84/54), 30 degrees in 1992 (86/56) and 30 degrees in 2005 (73/43).

On the cool side, in 2002 the high was 58 with the record low of 31 (the former record lows were 36 in both 1883 and 1997). In 1997 the high was 58 with a low of 36. In 1979 the high was 58 with a low of 38. Other cool highs were 57 in 2003 and 58 in 1990. The record coolest high of 42 occurred way back in 1883. 28 of the last 32 lows (88%) were in the: 40s (15) and 50s (13). Three lows were in the cold 30s. One low was in the warmer 60s (60 two years ago).

Tom Skilling/Chicago Weather Center Blog brought up 2002 as containing a five day string of sub-60 degree high temperature days. Indeed, the five days from May 17-21, 2002 were remarkably cold for this month. On May 17, the high of 45 and low of 36 were both records and it was the coldest May 17 in O'Hare's history. On May 18, the high of 54 and record low of 34 made it the coldest May 18 in O'Hare's history. On May 19, the high of 54 and low of 38 tied 2000 (48/44) as the coldest May 19 days in O'Hare's history. On May 20, the high of 48 and low of 33 made it the coldest May 20 in O'Hare's history. On May 21, the high of 58 and record low of 31 made it the coldest May 21 in O'Hare's history.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:54 and sunrise is at 5:27. Sunset is at 20:13 and twilight ends at 20:46. There's a total of 14 hours, 46 minutes of daylight today and 15 hours, 52 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:53 and sunrise is at 5:26. The moon is waning gibbous. Illumination was 83% at midnight, will be 79% at noon and 74% at midnight tonight. Moonset is at 9:24 this morning. Moonrise is at 0:11 tomorrow morning. Moonset is at 10:20 later in the morning. Moonlight time is 9 hours, 24 minutes which is 41 minutes longer than yesterday.

The warm part of Spring (Warm Spring) began on April 13. Warm Spring runs for 52 days, through June 3. High temperatures in this period are usually in the 50s, 60s and 70s. Warmer 80s and 90s occur infrequently. Armed Forces Day is today. National Maritime Day is tomorrow. Memorial Day is in nine days. -Bernie-