June 18: ORD

Today is June 18th. It's the 170th day of the year. 196 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 81 and the normal low is 59. I've calculated the 33-year averages at 82 and 59.

On the hot side, in 1995 (O'Hare's hottest June 18th) the high was 93 with O'Hare's only 70s low of the date of 71. The year earlier, 1994, the high was 94 with a low of 68. The other hot high was 95 in 1987 (O'Hare's hottest high of the date). The record high of 98 was set in 1954 at Midway. The record warmest low of 77 occurred in 1921, at a time when the official readings were taken adjacent to Lake Michigan. 24 of the past 33 highs (73%) were in the: 70s (9) and 80s (15). There were six consecutive 70s & 80s highs from 2004 through 2009. Seven highs (21%) were in the 90s. Two highs (6%) were in the cool 60s.

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1974 the high was 81 with a low of 51, a 30 degree spread. In 1965 the high was 75 with a cool low of 44 (a low colder than the record low), a 31 degree spread. In 1963 the high was 85 with a low of 53, a 32 degree spread. In 1961 the high was 81 with a low of 51, a 30 degree spread.

More recently, all the spreads were large: 36 degrees in 1988 (92/56), 33 degrees in 2003 (90/57), 32 degrees in 1993 (85/53), 30 degrees in 1986 (81/51) and 30 degrees in 1987 (95/65).

On the cool side, in 1982 (O'Hare's coolest June 18th) the high was 64 (O'Hare's coolest high of the date) with a low of 52. In 1999 the high was 73 with the record low of 45. The other cool high was 66 in 1979. The record coolest high of 55 occurred in 1950 at Midway. 31 of the last 33 lows (94%) were in the: 50s (16) and 60s (15). One low was in the cool 40s (the record low) and one was in the warm 70s (71 in 1995). O'Hare's coldest low is 44 in 1965, a low colder than the record low.

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 5:17. Sunset is at 20:33 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 2% at midnight, will be 1% at noon and 0% at midnight tonight. Moonrise was at 4:32 this morning. Moonset is at 19:50 tonight. Moonrise is at 5:22 tomorrow morning. Moonlight time is 15 hours, 18 minutes which is five minutes longer than yesterday. Moonlight time is at its peak today and tomorrow. 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. Independence Day is in 16 days.