July 15: ORD

Today is July 15th. It's the 197th day of the year. 169 days remain. It's week 29 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 85 and the normal low is 64. I've calculated the 33-year averages at 86 and 65.

On the hot side, in 1980 (O'Hare's warmest July 15th) the high was 98 with the record warmest low of 82. In 1995 (O'Hare's second warmest July 15th) the high was 98 with a low of 75. In 1988 (tied with 1977 as O'Hare's third warmest July 15th) the high was the record high of 102 with a low of 70, a 32 degree spread. In 2006 the high was 97 with a low of 74. 28 of the past 33 highs (85%) were in the: 80s (18) and 90s (10). We've had 80s & 90s highs for the past 19 consecutive years (since 1993). One high was in the hot 100s (the record of 102 in 1988). Four highs were in the cool 70s. Our most recent 70s high was 77 in 1992. Tied with 1988 as O'Hare's third warmest July 15th is 1977 as the high was 98 with a low of 74. Through 2011, this is the average second hottest day of the year.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1977 the high was a hot 98 with a low of 74, a hot day. In 1967 the high was 70 with a low of 49, a cool day. That low of 49 was colder than the record low of 52, which occurred this year (1967). In 1964 the high was 88 with a low of 56, a 32 degree spread. In 1962 the high was a cool 67 with a low of 60, a seven degree spread.

More recently, there was a small spread of seven degrees in 1981 (75/68). There were additional large spreads of 33 degrees in 1991 (87/54) and 31 degrees in 2002 (91/60).

On the cool side, in 1987 (O'Hare's second coolest July 15th) the high was 70 with a low of 54. Three years later, in 1990, the high was 72 with a low of 61.  The record low of 52 was last set in 1967 at Midway, having first been set in 1945 at Midway. The record coolest high of 65 occurred back in 1903, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the 60s (17) and 70s (9). There were consecutive 60s & 70s lows as follows: seven from 1994 through 2000 and seven from 2005 through last year, 2011. Six lows (18%) were in the cool 50s. Our most recent 50s low was 59 in 2004. One low (3%) was in the hot 80s (82 in 1980). O'Hare's coolest July 15th was in 1967 as the high was 70 with a low of 49, O'Hare's coldest low of the date and a low which is colder than the official record low. O'Hare's coolest high of the date is 67 degrees in 1962.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:57 and sunrise is at 5:31. Sunset is at 20:28 and twilight ends at 21:01. There's a total of 14 hours, 57 minutes of daylight today and 16 hours, 4 minutes between twilights. We lost a minutes of daylight from yesterday. Tomorrow twilight begins at 4:58 and sunrise is at 5:32. The moon is waning crescent. Illumination was 14% at midnight, will be 11% at noon and 8% at midnight tonight. Moonrise was at 2:28 this morning. Moonset is at 17:45 this afternoon. Moonrise is at 3:16 tomorrow morning. Moonlight time is 15 hours, 17 minutes which is 9 minutes longer than yesterday. Moonlight is at its peak today and tomorrow.

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. Parent's Day is in seven days.