May 20: ORD

Today is May 20th. It's the 140th day of the year. 225 days remain. It's week 20 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 47.

On the warm side, in 2004 the high was 84 with a low of 63. Two years ago, in 2009, the high was 84 with a low of 61. Another warm high was 84 in 1992. The record high of 95 and record warmest low of 70 were set on the same hot day in 1977 at Midway. 26 of the last 32 highs (81%) were in the: 60s (10) and 70s (16). Four highs were in the warmer 80s. Two highs were in the cold: 40s (1) and 50s (1).

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 78 with a low of 46, a 32 degree spread. In 1977 the high was 93 with a low of 64, a hot day and year of the record high and warmest low. In 1975 the high was 87 with a low of 67, another hot day. In 1972 the high was a hot 87 with a low of 54, a 33 degree spread. In 1970 the high was a warm 85 with a low of 52, a 33 degree spread. In 1965 the high was 74 with a low of 40, a 34 degree spread. In 1964 the high was a cool 58 degrees. In 1962 the high was a warm 85 with a low of 53, a 32 degree spread. In 1959 the low was a warm 64 degrees.

More recently, we had large spreads of 41 degrees in 1981 (76/35), 37 degrees in 1994 (78/41), 36 degrees in 2006 (74/38), 34 degrees in 1979 (78/44), 33 degrees in 1992 (84/51) and 31 degrees in 1980 (74/43).

On the cool side, in 2002 the high was 48 (the only 40s high) with the record low of 33 (the former record low was 35 in 1981). In 1986 the high was 56 (the only 50s high) with a low of 41. Other lows of note were 35 in 1981 and 38 in 2006. The record coolest high of 40 occurred way back in 1895. 26 of the last 32 lows (81%) were in the: 40s (17) and 50s (9). Our most recent 50s low was 54 back in 1998. Four lows were in the cold 30s. Two lows were in the warmer 60s.

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 4:55 and sunrise is at 5:28. Sunset is at 20:12 and twilight ends at 20:45. There's a total of 14 hours, 44 minutes of daylight today and 15 hours, 50 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:54 and sunrise is at 5:27. The moon is waning gibbous. Illumination was 90% at midnight, will be 87% at noon and 83% at midnight tonight. Moonset is at 8:18 this morning. Moonrise is at 23:35 tonight. Moonset is at 9:24 tomorrow morning. Moonlight time is 8 hours, 43 minutes which is 21 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 tomorrow. National Maritime Day is in two days. Memorial Day is in ten days. -Bernie-