July 1: ORD

Today is July 1st. It's the 183rd day of the year. 183 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 81 and 59.

On the hot side, in 2002 the high was 93 with a low of 75 (O'Hare's second warmest low of the date). In 1991 (tied with 1963 as O'Hare's second warmest July 1st) the high was 97 (O'Hare's hottest high of the date) with a low of 67, a 30 degree spread. The record high of 103 was set in 1956 at Midway. The record warmest low of 78 occurred back in 1931 at the University of Chicago. 25 of the past 33 highs (76%) were in the: 70s (12) and 80s (13). Six highs (18%) were in the hot 90s. Two highs (6%) were in the cool 60s. These were 65 degrees three years ago (in 2009) and 66 in 1986. O'Hare's warmest July 1st was in 1970 as the high was 94 (O'Hare's third hottest high of the date) with a low of 76 (O'Hare's warmest low of the date). Tied with 1991 as O'Hare's second warmest July 1st is 1963 with a high of 95 (O'Hare's second hottest high of the date) and low of 69.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1974 the high was 89 with a low of 57, a 32 degree spread. In 1970 the high was 94 with a warm low of 76, a hot day. In 1966 the high was 92 with a low of 61, a 31 degree spread. In 1965 the high was 81 with a cold low of 40, a 41 degree spread and cool day. In 1959 the high was a cool 71 degrees.

More recently, there were additional large spreads of: 34 degrees in 1989 (89/55), 33 degrees in 1979 (84/51) and 33 degrees in 1992 (91/58).

On the cool side, three years ago, in 2009, the high was 65 (O'Hare's coolest high of the date) with a low of 57. In 1982 the high was 76 with Chicago's official record low (but not O'Hare's coldest low of the date; see last line of this section) of 46, a 30 degree spread. 1982 and 2009 were O'Hare's second coolest July 1st days. The other cold lows were 49 in 1984, 50 in 2001 and 51 in 1979. These 40s lows were just two years apart! The other cool highs were 66 in 1986 (O'Hare's second coolest high of the date) and 70 in 1981. The record coolest high of 61 occurred back in 1924, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the last 33 lows (88%) were in the: 50s (16) and 60s (13). Two lows were in the cool 40s and two were in the warm 70s (75 in 2002 and 72 last year, in 2011). O'Hare's coolest July 1st was in 1965 as the high was 81 with a low of 40 (a low colder than the record low and thus O'Hare's coldest low of the date).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:47 and sunrise is at 5:21. Sunset is at 20:33 and twilight ends at 21:08. There's a total of 15 hours, 12 minutes of daylight today and 16 hours, 21 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 4:47 and sunrise is at 5:22. The moon is waxing gibbous, heading towards the full Buck moon in two days at 13:52. Illumination was 91% at midnight, will be 94% at noon and 97% at midnight tonight. Moonset was at 3:08 this morning. Moonrise is at 18:36 tonight. Moonset is at 4:08 tomorrow morning. Moonlight time is 8 hours, 32 minutes which is 15 minutes shorter 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 three days.