June 21: ORD

Today is June 21st. It's the 173rd day of the year. 193 days remain. It's week 25 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 82 and the normal low is 60. I've calculated the 33-year averages at 83 and 62.

On the hot side, in 1988 (O'Hare's hottest June 21st) the high was the record high of 101 with a low of 71 (O'Hare's co-warmest low of the date), a 30 degree spread. In 2002 the high was 88 with a low of 71 (O'Hare's other co-warmest low of the date). The record warmest low of 74 occurred back in 1923, at a time when the official readings were taken adjacent to Lake Michigan. 21 of the past 33 highs (64%) were in the 80s. O'Hare recorded seven consecutive 80s highs from 1993 through 1999. Four highs (12%) were in the hot: 90s (3) and 100s (1). O'Hare's only 90s highs of the date occurred from 1983 through 1991. Eight highs (24%) were in the cool: 60s (3) and 70s (5).

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1972 the high was a cool 68 with a low of 50, a cool day. In 1969 the high was 65 with a low of 46, a cool day. In 1967 the high was a cool 68 degrees. In 1963 the high was 64 with a low of 41, a cool day. In 1962 the high was 83 with a low of 53, a 30 degree spread. In 1961 the high was 75 with a cold low of 44, a 31 degree spread, a cool day. In 1960 the high was a cool 70 degrees.

More recently, the additional spreads were large: 33 degrees in 2003 (80/47), 30 degrees in 1986 (92/62) and 30 degrees in 1991 (93/63).

On the cool side, in 1992 (O'Hare's coolest June 21st) the high was 61 (O'Hare's coolest high of the date) with the record low of 38. In 2001 the high was 69 with a low of 55. The other cold low was 47 in 2003. The other cool high of 67 occurred in 2004. The record coolest high of 56 occurred way back in 1881, at a time when the official readings were taken adjacent to Lake Michigan. 20 of the last 33 lows (61%) were in the 60s. O'Hare recorded eight consecutive 60s lows from 1993 through 2000. Ten lows (30%) were in the cool: 30s (1), 40s (1) and 50s (8). Our most recent 50s low was 58 in 2004. Three lows (9%) were in the warm 70s. O'Hare's second coolest June 21st was in 1963 as the high was 64 with a low of 41.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:42 and sunrise is at 5:17. Sunset is at 20:33 and twilight ends at 21:08. There's a total of 15 hours, 16 minutes of daylight today and 16 hours, 26 minutes between twilights. We gained no minutes of daylight from yesterday. Tomorrow twilight begins at 4:43 and sunrise is at 5:17. The moon is waxing crescent, having reached new two days ago at 10:02. Illumination was 3% at midnight, will be 5% at noon and 7% at midnight tonight. Moonrise was at 7:18 this morning. Moonset is at 21:54 tonight. Moonrise is at 8:20 tomorrow morning. Moonlight time is 14 hours, 36 minutes which is 23 minutes shorter 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 in 13 days.