June 17: ORD

Today is June 17th. It's the 169th day of the year. 197 days remain. It's week 25 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 59. I've calculated the 33-year averages at 81 and 59.

On the hot side, in 1984 (O'Hare's hottest June 17th) the high was 92 with the record-tying warmest low of 77. The original record warmest low of 77 occurred in 1957 at Midway. In 2006 the high was 92 with a low of 72 (the co-second warmest low at O'Hare for the date). In 1994 the high was 93 (O'Hare's second hottest high of the date) with a low of 70. The other hot high was 94 in 1987, O'Hare's hottest high of the date. The record high of 96 was tied in 1957 at Midway, having first being set way back in 1887. Along with the co-record low of 77, this makes 1957 Chicago's warmest June 17th. 22 of the past 33 highs (67%) were in the: 70s (10) and 80s (12). Seven highs (21%) were in the hot 90s and four highs (12%) were in the cool 60s. O'Hare's second hottest June 17th was in 1977 as the high was 93 with a low of 72 (a co-second warmest low). 1970 also had a co-second warmest low of 72 degrees.

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1977 the high was 93 with a low of 72, a hot day. In 1976 the high was 85 with a low of 54, a 31 degree spread. In 1974 the high was a cool 65 with a low of 50, a cool day. In 1972 the high was 66 with a low of 46, a cool day. In 1970 the low was a warm 72 degrees. In 1965 the high was 69 with a cool low of 45, a cool day. In 1963 the high was 82 with a low of 48, a 34 degree spread. In 1961 the high was 79 with a low of 49, a 30 degree spread. In 1960 the high was a cool 64 with a low of 51, a cool day.

More recently, four spreads were large: 35 degrees in 1987 (94/59), 33 degrees in 2001 (87/54), 31 degrees in 1982 (76/45) and 30 degrees in 1989 (80/50).

On the cool side, in 1999 (O'Hare's co-second coolest June 17th) the high was 66 with a low of 48. In 1980 the high was 74 with the record low of 42. The other cool low was 45 in 1982. The other cool highs were 64 in 2000 (tied with 64 in 1960 as O'Hare's coolest highs of the date) and 67 in 1986. The record coolest high of 57 occurred way back in 1879, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (15) and 60s (11). Three lows (9%) were in the cool 40s and four (12%) were in the warm 70s. O'Hare's coolest June 17th was in 1972 as the high was 66 with a low of 46. O'Hare's co-second coolest June 17th was in 1965 as the high was 69 with a low of 45.

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 21:07. There's a total of 15 hours, 16 minutes of daylight today and 16 hours, 25 minutes between twilights. We gained no minutes of daylight from yesterday. Tomorrow twilight begins at 4:42 and sunrise is at 5:17. The moon is waning crescent. Illumination was 5% at midnight, will be 3% at noon and 2% at midnight tonight. Moonrise was at 3:47 this morning. Moonset is at 19:00 tonight. Moonrise is at 4:32 tomorrow morning. Moonlight time is 15 hours, 13 minutes which is 15 minutes longer than yesterday. Moonlight time is at its peak today and the next two days. Too bad that it will be difficult to see! 

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 today. Independence Day is in 17 days.