June 4: ORD

Today is June 4th. It's the 156th day of the year. 210 days remain. It's week 23 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 76 and the normal low is 54. I've calculated the 33-year averages at 73 and 51.

On the warm side, last year, in 2011, O'Hare had its warmest June 4th. The high was 92 (O'Hare's second warmest high of the date) with a low of 64 (O'Hare's warmest low of the date). In 1979 the high was 87 with a low of 63. The only other 60s low (from 1979 onward) was 60 in 1992. The record high of 97 was set in 1977 at Midway. The record warmest low of 75 occurred back in 1925, at a time when the official readings were taken adjacent to Lake Michigan. 24 of the past 33 highs (73%) were in the: 60s (9) and 70s (15). There were consecutive highs in the 60s & 70s as follows: six from 1987 through 1992 and six from 1995 through 2000. Seven highs (21%) were in the warm: 80s (6) and 90s (1). Two highs (6%) were in the cool 50s. O'Hare's second warmest June 4th was in 1977 as the high was its warmest high of 96 with a low of 58. O'Hare's third warmest high and only other 90s high was 90 in 1971.

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1978 the high was 80 with a low of 46, a 34 degree spread. In 1977 the high was a hot 96 with a low of 58, a 38 degree spread, overall hot day and day of the record high of 97 at Midway. In 1971 the high was a hot 90 with a low of 60, a 30 degree spread. In 1968 the high was 83 with a low of 48, a 35 degree spread. In 1967 the high was 80 with a low of 50, a 30 degree spread. In 1961 the high was 82 with a low of 48, a 34 degree spread.

More recently, there were large spreads of 37 degrees in 1994 (80/43), 34 degrees in 1984 (84/50) and 34 degrees in 1988 (79/45).
 
On the cool side, in 1993 (O'Hare's coolest June 4th) the high was 53 (O'Hare's coolest high of the date) with a low of 44. In 2001 the high was 55 with a low of 46. In 1982 the high was 61 with a low of 43. In 1990 the high was 61 with a low of 44. The other cold low was 42 in 2009, O'Hare's coldest low of June 4th. The other cool highs were 61 in 2000 and 62 in 1996. The record low of 35 was set in 1945 at Midway. The record coolest high of 47 occurred way back in 1891, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 40s (13) and 50s (17). Three lows were in the warm 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:44 and sunrise is at 5:18. Sunset is at 20:26 and twilight ends at 21:00. There's a total of 15 hours, 8 minutes of daylight today and 16 hours, 16 minutes between twilights. We  gained a minute of daylight from yesterday. Tomorrow twilight begins at 4:44 and sunrise is at 5:18. The moon reaches the full Strawberry (a.k.a. Rose or Hot) moon this morning at 6:12. Illumination was 100% at midnight, will be 100% at noon and 99% at midnight tonight. Moonset was at 5:25 this morning. Moonrise is at 20:55 tonight. Moonset is at 6:30 tomorrow morning. Moonlight time is 8 hours, 30 minutes which is seven minutes shorter than yesterday. Moonlight time is at its least today.

Summer begins today, 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. Flag Day is in ten days.