May 19: ORD

Today is May 19th. It's the 139th day of the year. 226 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 49. I've calculated the 32-year averages at 71 and 49.

On the warm side, in 1996 the high was 90 with the warmest and only 70s low of 72. In 1998 the high was 91 with a low of 66. Another high of note was 83 in 1987. The record high of 94 was set in 1975 and tied in 1977. The record warmest low of 74 occurred back in 1911. 23 highs over the last 32 years (72%) were in the: 60s (9) and 70s (14). Six highs were in the warmer: 80s (4) and 90s (2). Three highs were in the cooler: 40s (1) and 50s (2).

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 93 with a low of 63, a hot day, 30 degree spread and year of the record high. In 1976 the high was 76 with a low of 39, a 37 degree spread. In 1975 the high was 91 with a low of 66, a hot day and year of the record high. In 1972 the high was a warm 83 degrees. In 1970 the high was a warm 85 with a low of 55, a 30 degree spread. In 1964 the high was a hot 86 with a low of 47, a 39 degree spread and warm day. In 1962 the high was 91 with a low of 69, a hot day. In 1960 the high was 67 with a warm low of 61, a six degree spread. In 1959 the high was 87 with a low of 63, a hot day.

More recently, we had large spreads of 38 degrees in 1985 (79/41), 34 degrees in 1992 (75/41), 32 degrees in 1987 (83/51), 30 degrees in 1988 (74/44), 30 degrees in 1995 (76/46) and 30 degrees last year, in 2010 (74/44).

On the cool side, in 2000 the high was 48 (the only 40s high) with a low of 44, a four degree spread. Two years later, in 2002, the high was 54 with a low of 38. In 1986 the high was 55 with a low of 42. The record low of 36 was set in 1993, tying the original record low which was set way back in 1894. The record coolest high of 41 occurred way back in 1895. 27 of the last 32 lows (84%) were in the: 40s (18) and 50s (9). Two lows were in the cold 30s. Three lows were in the warmer: 60s (2) and 70s (1). Over the last eight years (2003-10), lows have switched between the 40s and 50s. Lows, in chronological order from 2003, were: 58, 44, 51, 43, 56, 40, 52 and 44.

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): It was the fifth coldest May 17 of the last 33 years with a high of 60 and low of 40. May 18 (Wed): the high of 57 and low of 49 was the ninth coldest May 18 of the last 33 years. So hopefully, this marks the end of the current (and historic) cold period.

The following is courtesy of Tom Skilling/Chicago Weather Center Blog:
Mid-May high temperatures the coolest here in 66 years; area moves into a fifth below normal day
Chicago's high temperatures between May 14 and 17 have been the chilliest observed at O'Hare since official observations began at the Northwest side site in 1959. Expanding the comparison of these highs to the entire 141-year meteorological record for the city reveals a chillier mid-May period hasn't occurred in the 66 years since 1945.

Tom Skilling/Chicago Weather Center Blog also 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 4:56 and sunrise is at 5:29. Sunset is at 20:11 and twilight ends at 20:44. There's a total of 14 hours, 42 minutes of daylight today and 15 hours, 48 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:55 and sunrise is at 5:28. The moon is waning gibbous, having passed the full Flower moon two days ago at 6:09. Illumination was 96% at midnight, will be 93% at noon and 90% at midnight tonight. Moonset is at 7:13 this morning. Moonrise is at 22:51 tonight. Moonset is at 8:18 tomorrow morning. Moonlight time is 8 hours, 22 minutes which is six 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 in two days. National Maritime Day is in three days. Memorial Day is in 11 days. -Bernie-