July 13: ORD

Today is July 13th. It's the 195th day of the year. 171 days remain. It's week 28 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 84 and 64.

On the hot side, in 1995 (O'Hare's warmest July 13th) the high was the record high of 104 with the record warmest low of 81. That high of 104 is tied with June 20, 1988 as O'Hare's hottest temperature in its history. Two years later, in 1997 (O'Hare's third warmest July 13th), the high was 94 with a low of 72. 25 of the past 33 highs (76%) were in the: 70s (10) and 80s (15). O'Hare recorded 14 consecutive 70s & 80s highs from 1998 through last year, 2011. Seven highs (21%) were in the hot: 90s (6) and 100s (1). Our most recent 90s high was 94 in 1997. One high (3%) was in the cool 60s (66 in 1990, O'Hare's coolest high of the date). O'Hare's: second warmest July 13th was in 1973 (high of 95, low of 72) and fourth warmest July 13th was in 1974 (high of 95, low of 69).

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1976 the high was 86 with a low of 53, a 33 degree spread. In 1974 the high was a hot 95 with a low of 69, hot but not a hot day compared to normal. In 1973 the high was a hot 95 with a low of 72, hot but not a hot day compared to normal. In 1967 the high was 67 with a low of 52, a cool day. That low of 52 was equal to the record low. In 1964 the high was 71 with a low of 49, a cool day. That low of 49 was colder than the record low.

More recently, there was a large spread of 33 degrees in 1983 (89/56).

On the cool side, in 1990 the high was 66 (O'Hare's coolest high of the date) with a low of 59, a seven degree spread. Three years earlier, in 1987, the high was 74 with a low of 54. The other cool high was 72 in 1994. The record low of 52 was set in 1975 at Midway. The record coolest high of 64 occurred back in 1926 at the University of Chicago. 18 of the last 33 lows (55%) were in the 60s. Nine lows (27%) were in the cold 50s. Six lows (18%) were in the warm: 70s (5) and 80s (1). O'Hare's coolest July 13th was in 1967 as the high was 67 (O'Hare's second coolest high of the date) with a low of 52 (equal to the record low). O'Hare's second coolest July 13th was in 1964 as the high was 71 with a low of 49 (O'Hare's coldest low of the date and only 40s low of the date). That low of 49 is also colder than the official record low.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:55 and sunrise is at 5:29. Sunset is at 20:29 and twilight ends at 21:02. There's a total of 15 hours of daylight today and 16 hours, 7 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:56 and sunrise is at 5:30. The moon is waning crescent. Illumination was 30% at midnight, will be 26% at noon and 22% at midnight tonight. Moonrise was at 1:08 this morning. Moonset is at 15:57 this afternoon. Moonrise is at 1:45 tomorrow morning. Moonlight time is 14 hours, 49 minutes which is 24 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. Parent's Day is in nine days.