August 10: ORD

Today is August 10th. It's the 223rd day of the year. 143 days remain. It's week 32 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 83 and the normal low is 64. I've calculated the 33-year averages at 82 and 64.

On the hot side, two years ago, in 2010 (O'Hare's warmest August 10th) the high was 89 with a low of 75 (O'Hare's warmest low of the date). In 1992 the high was 91 (along with a high of 91 in 1983, O'Hare's second hottest highs) with a low of 68. Three years later, in 1995, the high was 89 with a low of 70.  The record high of 99 was set in 1944 at Midway. The record warmest low of 79 occurred in 1938 at the University of Chicago. 19 of the past 33 highs (58%) were in the 80s. Three highs (9%) were in the hot 90s. 11 highs (33%) were in the cool: 60s (3) and 70s (8). O'Hare's hottest high of the date was 93 degrees in 1971. O'Hare's second warmest August 10th was in 1977 as the high was 88 with a low of 74. That low of 74 in 1977 is tied with a low of 74 in 2006 as O'Hare's second warmest lows of the date.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1974 the high was 75 with a low of 72, a three degree spread. In 1972 the low was a cold 52 degrees. In 1967 the high was a cool 69 with a low of 53, a cool day. In 1966 the high was a cool 67 with a low of 61, a six degree spread. In 1965 the high was 70 with a low of 50, a cool day. In 1960 the high was a cool 68 degrees.

More recently, there was a large spread of 30 degrees in 2002 (89/59). The small spreads were five degrees in 2006 (79/74), seven degrees in 1988 (80/73) and seven degrees in 2004 (67/60).
 
On the cool side, in 1982 (O'Hare's coolest August 10th) the high was 68 (O'Hare's second coolest high of the date) with the record low of 49. The record low of 49 was originally set a decade earlier, in 1972 at Midway. In 1994 the high was 67 with a low of 56. The other cool 60s high (and most recent) was 67 in 2004. The record coolest high of 66 was set way back in 1882, at a time when the official readings were taken adjacent to Lake Michigan. 21 of the last 33 lows (64%) were in the 60s. Six lows (18%) were in the cool: 40s (1) and 50s (5). Six lows (18%) were in the warm 70s. Four of the six 70s lows (67%) occurred from 2006 through 2010. O'Hare's second coolest August 10th was in 1965 as the high was 70 with a low of 50 (O'Hare's second coldest low of the date). O'Hare's coolest highs of the date were 67 degrees in 1966, 1994 and 2004. O'Hare's third coolest high was 69 degrees in 1967.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:25 and sunrise is at 5:56. Sunset is at 20:00 and twilight ends at 20:31. There's a total of 14 hours, 4 minutes of daylight today and 15 hours, 6 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:26 and sunrise is at 5:57. The moon is waning crescent, having reached last quarter yesterday at 13:55. Illumination was 46% at midnight, will be 41% at noon and 36% at midnight tonight. Moonset is at 14:43 this afternoon. Moonrise is at 0:23 tomorrow morning. Moonset is at 15:36 tomorrow afternoon. Moonlight time is 14 hours, 43 minutes which is 39 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. Labor Day is in 24 days.