July 2: ORD

Today is July 2nd. It's the 184th day of the year. 182 days remain. It's week 27 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 84 and the normal low is 63. I've calculated the 33-year averages at 83 and 60.

On the hot side, in 2002 the high was 93 with a low of 75 (O'Hare's second warmest low of the date). Last year, in 2011, the high was 94 (O'Hare's third hottest high of the date) with a low of 71. Two decades earlier, in 1991, the high was 96 (O'Hare's hottest high of the date) with a low of 68. The record high of 99 was set in 1970 at Midway. The record warmest low of 79 occurred back in 1911, at a time when the official readings were taken adjacent to Lake Michigan. 20 of the past 33 highs (61%) were in the 80s. Ten highs (30%) were in the cool 70s. Three highs (9%) were in the hot 90s. O'Hare's warmest July 2nd was in 1970 as the high was 95 (O'Hare's second hottest high of the date) with a low of 78 (O'Hare's warmest low of the date). The other pre-1979 warm low was 74 in 1973 (O'Hare's third warmest low of the date).
 
In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1978 the high was 73 with a low of 66, a seven degree spread. In 1973 the low was a warm 74 degrees. In 1970 the high was 95 with a low of 78, a hot day and year of the record high of 99 at Midway. In 1968 the high was a cool 67 with a low of 51, a cool day. In 1966 the high was 93 with a low of 59, a 34 degree spread.

More recently, there were large spreads of: 34 degrees in 1984 (83/49) and 32 degrees in 1979 (82/50).

On the cool side, in 2001 the high was 75 with the record low of 49. The record low of 49 was originally set in 1984. In 1982 the high was 73 with a low of 51. 1982 and 2001 were O'Hare's second coolest July 2nd days. O'Hare's second coolest high was 70 in 1994. The record coolest high of 62 occurred in 1940 at the University of Chicago. 29 of the last 33 lows (88%) were in the: 50s (14) and 60s (15). Two lows were in the cold 40s (the record lows). Two lows were in the warm 70s (75 in 2002 and 71 last year, in 2011). 1968 was O'Hare's coolest July 2nd as the high was 67 (O'Hare's coolest high of the date) with a low of 51.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:47 and sunrise is at 5:22. Sunset is at 20:33 and twilight ends at 21:08. There's a total of 15 hours, 11 minutes of daylight today and 16 hours, 21 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:48 and sunrise is at 5:22. The moon is waxing gibbous, heading towards the full Buck moon tomorrow at 13:52. Illumination was 97% at midnight, will be 98% at noon and 100% at midnight tonight. Moonset was at 4:08 this morning. Moonrise is at 19:35 tonight. Moonset is at 5:15 tomorrow morning. Moonlight time is 8 hours, 33 minutes which is a minute longer than yesterday. Moonlight time is at its least today for the next several days.

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 two days.