July 3: ORD

Today is July 3rd. It's the 185th day of the year. 181 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 62.

On the hot side, in 1999 (tied with 1974 as O'Hare's warmest July 3rd) the high was 92 with a low of 76 (O'Hare's warmest low of the date). In 2002 the high was 94 (with 1974, O'Hare's hottest high of the date) with a low of 73. The record high of 102 was set in 1949 at Midway. The record warmest low of 78 occurred back in 1911, at a time when the official readings were taken adjacent to Lake Michigan. 28 of the past 33 highs (85%) were in the: 70s (10) and 80s (18). Five highs were in the hot 90s. Our most recent 90s highs were 94 in 2002 and 93 in 2003. One temperature quirk was that back in 1935, this was the date of the first high of 85 degrees or more for that year! Official readings were taken at the University of Chicago at the time. In 1974 (tied with 1999 as O'Hare's warmest July 3rd) the high was 94 (with 2002, O'Hare's hottest high of the date) with a low of 74 (O'Hare's second 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 1971 the high was 87 with a low of 57, a 30 degree spread. In 1968 the high was 75 with a cold low of 48 degrees. In 1967 the high was a cool 71 degrees with a low of 51, a cool day. In 1963 the high was 67 with a low of 48, a cool day. That low of 48, just as with 1968, was colder than the record low.

More recently, there were large spreads of: 34 degrees in 1988 (86/52), 32 degrees in 2005 (86/54), 30 degrees in 1979 (85/55), 30 degrees in 1980 (80/50) and 30 degrees in 1985 (83/53).

On the cool side, in 2008 the high was 71 with a low of 55. In 1996 the high was 76 with a low of 53. A decade earlier, in 1986, the high was 77 with a low of 52. The record low of 50 was set in 1980. The other cool high was 72 in 2000. The record coolest high of 63 occurred way back in 1909, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 50s (11) and 60s (19). Three lows were in the warm 70s. O'Hare's coolest July 3rd was in 1963 as the high was 67 (O'Hare's coolest high of the date) with a low of 48 (with 1968, O'Hare's coldest low of the date). O'Hare's second coolest July 3rd was in 1967 as the high was 71 with a low of 51. O'Hare's third coolest July 3rd was in 1968 as the high was 75 with a low of 48. The lows of 48 in 1963 and 1968 are colder than the record low.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:48 and sunrise is at 5:22. Sunset is at 20:33 and twilight ends at 21:07. There's a total of 15 hours, 11 minutes of daylight today and 16 hours, 19 minutes between twilights. We lost no minutes of daylight from yesterday. Tomorrow twilight begins at 4:48 and sunrise is at 5:23. The moon reaches the full Buck moon today at 13:52. Illumination was 100% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset was at 5:15 this morning. Moonrise is at 20:26 tonight. Moonset is at 6:27 tomorrow morning. Moonlight time is 8 hours, 49 minutes which is 16 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. Independence Day is tomorrow.