May 17: ORD

Today is May 17th. It's the 137th day of the year. 228 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 70 and the normal low is 48. I've calculated the 32-year averages at 70 and 48.

On the warm side, in 2001 the high was 85 with a low of 62. In 1982 the high was 87 with a low of 56, a 31 degree spread. Other 80s highs of note were 89 in 1987, 88 in 1996, 86 in 1998, 85 in 1984 and 82 in 1992. Another warm low was 62 in 1999. The record high of 94 was set in 1962 and the record warmest low of 70 occurred in 1977. 16 highs over the last 32 years (50%) were in the: 40s (1), 50s (5) and 60s (10). 16 highs (50%) were in the warmer: 70s (6) and 80s (10). Our most recent 80s high was 80 in 2004.

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1977 the high was 86 with a low of 63, a hot day and year of the record warmest low of 70 at Midway. In 1975 the high was 74 with a low of 43, a 31 degree spread. In 1973 the low was a cold 36 degrees. In 1972 the high was 80 with a low of 50, a 30 degree spread. In 1971 the high was a hot 88 with a low of 48, a 40 degree spread. In 1967 the high was 74 with a low of 44, a 30 degree spread. In 1964 the high was 80 with a low of 49, a 31 degree spread. In 1962 the high was 92 with a low of 71, a hot day. 1962 was also the year of the record high of 94 at Midway.

More recently, we had a small spread of seven degrees in 1980 (56/49). The large spreads were: 40 degrees in 1984 (85/45), 39 degrees in 1996 (88/49), 38 degrees in 1987 (89/51), 36 degrees in 1998 (86/50), 35 degrees in 1989 (80/45) and 30 degrees in 1992 (82/52).

On the cool side, in 2002 the record coolest high of 45 was established (broke the former record of 46 in 1945). The low in 2002 was 36, the record low. This ties the original record of 36, set in 1973. In 1983 the high was 58 with a low of 37. Other cool highs were 55 in 1981, 56 in 1980 and 58 last year in 2010. 26 of the last 32 lows (81%) were in the: 40s (15) and 50s (11). Four lows were in the cold 30s. Two lows were in the warmer 60s.

The past few days have been wildly cool this year. May 14 (Sat.): high of 53, low of 45, nine below normal; tied 2006 (56/42) as third coldest. The coldest days were 10.5 below normal: 1981 (50/45) and 1996 (57/38). May 15 (Sun.): It was the coldest May 15 in O'Hare's history as the high of 46 and low of 41 made the day 14.5 degrees below normal. It beat the prior two coldest days of 1997 (51/38), -13.5 of normal and 1983 (53/37), -13 of normal. The high of 46 is just two degrees above the record coldest high of 44 set way back in 1904. May 16 (Mon.): It was the coldest May 16 in O'Hare's history as the high of 52 and low of 37 made the day 14.5 degrees below normal. It beat the prior coldest day of 1983 (63/35), -10 of normal. The high of 52 was cooler than our other 50s high of 57 in 1996. May 17 (Tue): Today is on course to be one of the coldest May 17ths in the history of O'Hare (going back to 1959). A high in the upper 50s is predicted after a low of 40 this morning.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:58 and sunrise is at 5:31. Sunset is at 20:09 and twilight ends at 20:42. There's a total of 14 hours, 38 minutes of daylight today and 15 hours, 44 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:57 and sunrise is at 5:30. The moon is full as the full Flower moon today at 6:09. Illumination was 100% at midnight, will be 100% at noon and 99% at midnight tonight. Moonset is at 5:20 this morning. Moonrise is at 20:54 tonight. Moonset is at 6:13 tomorrow morning. Moonlight time is 8 hours, 26 minutes which is 27 minutes shorter 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 in four days. National Maritime Day is in five days. Memorial Day is in 13 days. -Bernie-