July 27: ORD

Today is July 27th. It's the 208th day of the year. 157 days remain. It's week 30 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.

According to the National Climatic Data Center (NCDC), the normal high is 84 and the normal low is 64. I've calculated the 32-year averages at 84 and 64.

On the hot side, in 1989 the high was 93 with a low of 73, our warmest low. In 1997 the high was 92 with a low of 72. The other 90s highs were 93 in 1988, 92 in 1983 and 90 in 1995. Note that in the back-to-back years of 1988 and 1989, the high was our warmest 93 degrees. The record high of 100 was set back in 1916 and tied in 1955. The record warmest low of 82 occurred back in 1916. 19 of the past 32 highs (59%) were in the 80s. Five highs (16%) were in the hot 90s. Eight highs (25%) were in the cool: 60s (1) and 70s (7). There is an ongoing, sub-90 degree string of high temperatures, from 1998 to 2010 (the past 13 years).

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1977 the low was a cool 52 degrees. In 1972 the high was a cool 71 degrees. In 1964 the high was 89 with a low of 59, a 30 degree spread. In 1962 the low was a cool 51 degrees.

More recently, there was a small spread of six degrees in 1981 (69/63). The large spreads were 35 degrees in 1985 (87/52), 33 degrees in 1979 (89/56) and 33 degrees in 1988 (93/60).

On the cool side, in 1984 the high was 74 with a low of 55. In 2005 the high was 74 with a low of 56. The record low of 52 was set in 1985 and the record coolest high of 69 occurred in 1981. Another cool high of 74 occurred in 1980. 17 of the last 32 lows (53%) were in the 60s. Nine lows (28%) were in the cool 50s. Six lows (19%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:09 and sunrise is at 5:41. Sunset is at 20:18 and twilight ends at 20:50. There's a total of 14 hours, 37 minutes of daylight today and 15 hours, 41 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:10 and sunrise is at 5:42. The moon is waning crescent, heading towards new in three days. Illumination was 14% at midnight, will be 11% at noon and 8% at midnight tonight. Moonrise is at 2:21 this morning. Moonset is at 17:56 this afternoon. Moonrise is at 3:21 tomorrow morning. Moonlight time is 15 hours, 35 minutes which is 2 minutes longer than yesterday. Moonlight time is at it's peak today.

Summer began June 4 and runs for 110 days through September 21. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Labor Day is in 40 days.