June 15: ORD

Today is June 15th. It's the 167th day of the year. 199 days remain. It's week 24 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 80 and the normal low is 58. I've calculated the 33-year averages at 79 and 59.

On the hot side, in 1994 (O'Hare's hottest June 15th) the high was the record high of 95 with the record warmest low of 78. The record high of 95 also occurred 40 years earlier at Midway in 1954 and two years before that, in 1952 (also at Midway). In 1979 (O'Hare's third warmest June 15th) the high was 89 with a low of 72. The other hot high was 93 in 1988. 27 of the past 33 highs (82%) were in the: 70s (12) and 80s (15). Three highs were in the hot 90s. Three highs were in the cool: 50s (1) and 60s (2). O'Hare's second warmest June 15th was in 1967 as the high was 91 with a low of 74 (O'Hare's second warmest low of the date).

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1969 the high was a cool 68 degrees. In 1967 the high was 91 with a warm low of 74, a hot day. In 1965 the high was 67 with a low of 45, a cool day. In 1963 the low was a cold 46 degrees. In 1962 the high was 82 with a low of 50, a 32 degree spread. In 1961 the high was 63 with a low of 43, a cool day.

More recently, the additional spreads were large: 39 degrees in 1997 (82/43) and 32 degrees in 1995 (89/57).

On the cool side, in 1989 (O'Hare's second coolest June 15th) the high was 57 (O'Hare's coolest high of the date and only 50s high) with a low of 53, a spread of just 4 degrees. A decade later, in 1999, the high was 63 with a low of 52. The record low of 43 was set in 1997. The low was also 43 in 1961. The former record low of 46 occurred eight decades before in 1917. The record coolest high of 52 occurred in 1917, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the last 33 lows (88%) were in the: 50s (16) and 60s (13). Two lows were in the cool 40s and two were in the warm 70s. 1961 was O'Hare's coolest June 15th as the high was 63 with a low of 43 (equal to the current record low set in 1997). 

In regards to last year, 2011: the 45 degree drop in temperature from the high of 95 on 6/8/11 to the low of 50 late 6/9/11 was the greatest two-day drop in temperature since the June record drop of 49 degrees in 1988, 24 years ago. The drop in 1988 was from a high of 103 on June 25 to a low of 54 on June 26. The all-time record, irregardless of month, was a 61 degree drop from 74 degrees to 13 degrees on November 11 and 12, 1911. Data courtesy of The Chicago Weather Center Blog.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:42 and sunrise is at 5:16. Sunset is at 20:32 and twilight ends at 21:06. There's a total of 15 hours, 16 minutes of daylight today and 16 hours, 24 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:42 and sunrise is at 5:16. The moon is waning crescent. Illumination was 17% at midnight, will be 13% at noon and 10% at midnight tonight. Moonrise was at 2:33 this morning. Moonset is at 17:09 this afternoon. Moonrise is at 3:08 tomorrow morning. Moonlight time is 14 hours, 36 minutes which is 28 minutes longer than yesterday. 

Summer began on June 4th and runs for 110 days through September 21st. High temperatures in this period are usually in the 70s and 80s. Highs in the 90s and 100s occur infrequently. Father's Day is in two days.