May 13: ORD

Today is May 13th. It's the 134th day of the year. 232 days remain. It's week 20 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 69 and the normal low is 47. I've calculated the 33-year averages at 68 and 47.

On the warm side, in 1991 (O'Hare's warmest May 13th) the high was the record high of 89 (tying the original record high set in 1956) with a low of 64. In 2004 the high was 78 with a low of 65 (O'Hare's warmest low of the date). The other hot high was 86 in 1982. The only other warm low was 61 in 1983. The record warmest low of 72 occurred in 1956. So as you can see, 1956 was Chicago's warmest day, having a high of 89 and low of 72. 24 of the last 33 highs (73%) were in the: 60s (10) and 70s (14). O'Hare recorded six consecutive 60s & 70s highs from 1983 through 1988. On the warm side, two highs (6%) were in the 40s. On the cold side, seven highs (21%) were in the 50s.

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1977 the high was a warm 82 with a low of 57, a warm day. In 1975 the high was 73 with a low of 37, a 36 degree spread. In 1973 the high was a cool 57 degrees. In 1971 the high was 73 with a low of 37, a 36 degree spread. In 1968 the high was 77 with a low of 43, a 34 degree spread. In 1966 the high was a cold 44 with a low of 40, a four degree spread and cold day. In 1964 the high was a cool 51 with a low of 40, a cool day. In 1962 the high was a warm 84 with a low of 57, a warm day. In 1961 the high was 86 with a low of 61, a hot day.

More recently, we had a small spread of five degrees in 1999 (53/48). The large spreads were: 38 degrees in 1987 (78/40), 35 degrees in 1982 (86/51), 33 degrees in 2008 (73/40), 32 degrees in 1984 (72/40), 31 degrees in 2001 (68/37) and 30 degrees last year, in 2011 (77/47).
 
On the cool side, in 1996 (O'Hare's second coldest May 13th) the high was 56 with the record low of 34. The record low of 34 also occurred way back in 1888. A decade later, in 2006, the high was 50 with a low of 42. The other cool highs were 53 in 1999, 55 in 1997, 56 in 2002 and 57 in 1993. The record coldest high of 43 was set in 1953 at Midway. 23 of the last 33 lows (70%) were in the 40s. O'Hare recorded seven consecutive 40s lows from 1984 through 1990. Three lows (9%) were in the cold 30s. Seven lows (21%) were in the warm: 50s (4) and 60s (3). O'Hare's coldest May 13th was in 1966 as the high was O'Hare's coldest of 44 with a low of 40.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:02 and sunrise is at 5:34. Sunset is at 20:06 and twilight ends at 20:38. There's a total of 14 hours, 32 minutes of daylight today and 15 hours, 36 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:01 and sunrise is at 5:33. The moon is waning crescent, having reached last quarter yesterday at 16:47. Illumination was 47% at midnight, will be 42% at noon and 37% at midnight tonight. Moonrise was at 1:47 this morning. Moonset is at 13:20 this afternoon. Moonrise is at 2:14 tomorrow morning.  Moonlight time is 11 hours, 33 minutes which is 34 minutes longer than yesterday. 

Spring began on March 12th and runs for 84 days through June 3rd. Warm Spring began on April 13th and runs for 52 days through June 3rd. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 80s and 90s occur infrequently. Mother's Day is today. Armed Forces Day is in six days. National Maritime Day is in nine days.