July 20: ORD

Today is July 20th. It's the 201st day of the year. 164 days remain. It's week 29 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 85 and 65.

On the hot side, in 1980 the high was the record high of 101 with a low of 69, a spread of 32 degrees. In 1991 the high was 96 with a low of 74, our warmest low. Other hot highs were 96 in 1987, 94 in 1983 and 93 in 2001. The record warmest low of 79 occurred in 1977 at Midway. 31 of the past 32 highs (97%) were in the: 70s (9), 80s (14) and 90s (8). One high, the record high, was in the 100s. From 1979-2010, this is the average tenth hottest day of the year.

Yesterday's low at O'Hare was 78 degrees. This ties record for the warmest low temperature for July 19th with the year 1977. The high yesterday was 93 at 15:46 with that record-tying low of 78 at 6:36. This ties 1991 (high of 99, low of 72) as the warmest July 19th of the past 33 years. Rockford had a record-tying high of 100 at 15:29 with a record-breaking warm low of 76 at 5:58. Rockford's previous high of 100 occurred in 1930 and it's former record warmest low of 75 occurred in 1942.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1977 the high was 95 with a warm low of 76, a hot day and year of the record warmest low of 79. In 1972 the low was a warm 77 degrees. In 1970 the high was a cool 72 degrees. 1970 was the year of the record low. That low was 55 at O'Hare and cooler at Midway (53 degrees). In 1966 the low was a cool 51 degrees.

More recently, there were no other large spreads of at least 30 degrees or no small spreads of up to seven degrees.

On the cool side, in 1996 the high was 71 with a low of 59. Two years ago, in 2009, the high was 76 with a low of 55. Our lowest temperature was 54 in 1979. The record low of 53 was set in 1970 at Midway. Another cool high was 72 in 1989. The record coolest high of 65 occurred in 1950. 19 of the last 32 lows (59%) were in the 60s. Seven lows (22%) 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 5:01 and sunrise is at 5:34. Sunset is at 20:24 and twilight ends at 20:57. There's a total of 14 hours, 50 minutes of daylight today and 15 hours, 56 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 5:02 and sunrise is at 5:35. The moon is waning gibbous. Illumination was 77% at midnight, will be 73% at noon and 68% at midnight tonight. Moonset is at 11:09 this morning. Moonrise is at 22:47 tonight. Moonset is at 12:08 tomorrow afternoon. Moonlight time is 12 hours, 22 minutes which is 37 minutes longer than yesterday.

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. Parent's Day is in four days.