May 28: ORD

Today is May 28th. It's the 149th day of the year. 217 days remain. It's week 22 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 74 and the normal low is 52. I've calculated the 33-year averages at 73 and 52.

On the warm side, in 2006 (O'Hare's warmest May 28th) the high was a near-record 92 degrees (until 2012, the record was 93 in 1977) with the record warmest low of 74 (the former record warmest low is 72 in 1941). In 1991 (until 2012, O'Hare's second warmest May 28th) the high was 91 with a low of 69. In 1987 the high was 88 with a low of 68. In 1998 the high was 90 with a low of 60, a 30 degree spread. In 1999 the high was 87 (our most recent 80s high) with a low of 63 (our most recent 60s low). The other warm high was 88 in 1988. 22 of the past 33 highs (67%) were in the: 60s (11) and 70s (11). There were six consecutive 60s & 70s highs from 2000 through 2005. Eight highs (24%) were in the warm: 80s (5) and 90s (3). Our most recent 80s high was 87 in 1999. Three highs (9%) were in the cool 50s. Until 2012, O'Hare's third warmest May 28th was in 1969 (high of 90, low of 67). The other pre-1979 warm high was 88 in 1978. O'Hare's other pre-1979 warm low was 65 in 1959.

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 hot 88 with a low of 62, a hot day. In 1977 the high was a hot 93 with a low of 56, a 37 degree spread and hot day. 1977 was the year of the record high. In 1972 the high was a hot 88 degrees. In 1971 the high was 68 with a cold low of 38, a 30 degree spread. In 1970 the high was 80 with a low of 50, a 30 degree spread. In 1969 the high was 90 with a low of 67, a hot day. In 1968 the high was a cool 61 degrees. In 1967 the high was a cool 62 degrees. In 1965 the high was 52 with a low of 38, a cold day. In 1964 the high was a cool 59 with a low of 44, a cool day. In 1959 the high was 84 with a warm low of 65, a warm day.

More recently, there was a small spread of six degrees in 1983 (59/53). There were large spreads of 34 degrees in 1994 (80/46), 33 degrees in 1981 (79/46) and 30 degrees in 1989 (72/42).

On the cool side, in 1984 (O'Hare's second coolest May 28th) the high was 51 (O'Hare's coolest high of the date) with a low of 40. In 1992 the high was 69 with the record low of 33, a 36 degree spread. In 1996 the high was 57 with a low of 46. The other cool highs were 59 in 1983, 60 in 2000, 60 in 2004, 61 in 1985, 62 in 2008 and 62 last year, in 2011. The record coolest high of 47 occurred way back in 1884, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 40s (11) and 50s (15). One low (3%) was in the cold 30s and six (18%) were in the warm: 60s (5) and 70s (1). O'Hare's coolest May 28th was in 1965 as the high was O'Hare's second coolest high for the date of 52 and low of 38. The other pre-1979 cold low was 38 in 1971.  

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1991 the high was 91 with a low of 69,  overall 17 degrees ABOVE normal. Then in 1992 the high was 69 with a low of 33, overall 12 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:48 and sunrise is at 5:21. Sunset is at 20:20 and twilight ends at 20:54. There's a total of 14 hours, 59 minutes of daylight today and 16 hours, 6 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:47 and sunrise is at 5:21. The moon reaches first quarter today at 15:16. Illumination was 44% at midnight, will be 49% at noon and 55% at midnight tonight. Moonset was at 0:52 this morning. Moonrise is at 12:37 this afternoon. Moonset is at 1:21 tomorrow morning. Moonlight time is 12 hours, 15 minutes which is 37 minutes shorter than yesterday. 

Spring began on March 12th and runs for 84 days through June 3rd. Warm Spring began 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 occur infrequently. Memorial Day is today. Flag Day is in 17 days.