May 27: ORD

Today is May 27th. It's the 147th day of the year. 218 days remain. It's week 21 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 73 and the normal low is 51. I've calculated the 32-year averages at 72 and 50.

On the warm side, in 1987 the high was 88 with a low of 68. Four years later, in 1991, the high was 88 with a low of 66. The only other 60s low was 61 last year (in 2010). Other 80s highs of note were 87 in 2006 and 85 in 1980. The record high of 94 and record warmest low of 75 were set on the same hot day way back in 1911. 23 of the past 32 highs (72%) were in the: 60s (12) and 70s (11). Our most recent 60s high was 61 in 2001. Even warmer, seven highs were in the 80s. Two highs were in the cool 50s.

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1978 the high was 88 with a low of 66, a hot day. In 1976 the high was 77 with a low of 46, a 31 degree spread. In 1971 the low was a cold 38 degrees. In 1970 the high was a cool 61 degrees. In 1969 the high was 87 with a low of 63, a hot day. In 1968 the high was a cool 61 with a low of 54, a seven degree spread. In 1966 the high was a warm 85 with a low of 54, a 31 degree spread. In 1963 the high was a cool 60 degrees. In 1962 the high was a cool 59 degrees. In 1961 the high was 70 with a cold low of 34, a 36 degree spread. In 1959 the high was 83 with a warm low of 66, a warm day.

More recently, there was a small spread of six degrees in 1996 (54/48). There were large spreads of 35 degrees in 1999 (81/46), 33 degrees in 1980 (85/52), 33 degrees in 1998 (83/50) and 32 degrees in 1994 (67/35).

On the cool side, three years ago (in 2008) the high was 50 with a low of 42. In 1992 the high was 63 with the record low of 33, a 30 degree spread. The other 30s low was 35 in 1994. These were the only 30s lows, only two years apart. Other cool highs were 54 in 1996 and 61 in 2001. The record coolest high of 49 occurred way back in 1895. 27 of the last 32 lows (84%) were in the: 40s (15) and 50s (12). Two lows were in the cold 30s and three lows were in the warmer 60s.

Yesterday (May 26) was one of the coldest May 26 days we've ever had. The high of 49 and low of 43 at O'Hare was the second coldest (of the last 33 years) behind 1992's high of 53 and low of 35. The high of 49 was just a degree above the record coolest high of 48 which was set at Midway in 1961. O'Hare had a high of 47 in 1961. This was just the second 40s high ever at O'Hare on a May 26. According to Richard Koeneman of The Chicago Weather Center Blog, it was just the 4th May 26 that the high temperature failed to reach at least 50. This goes all the way back to 1871, so it's a total of 141 years and just 2.8% of May 26 days.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:49 and sunrise is at 5:22. Sunset is at 20:19 and twilight ends at 20:52. There's a total of 14 hours, 57 minutes of daylight today and 16 hours, 3 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:48 and sunrise is at 5:22. The moon is waning crescent. Illumination was 27% at midnight, will be 23% at noon and 19% at midnight tonight. Moonrise is at 2:18 this morning. Moonset is at 15:32 this afternoon. Moonrise is at 2:42 tomorrow morning. Moonlight time is 13 hours, 14 minutes which is 35 minutes longer than yesterday.

The warm part of Spring (Warm Spring) began on April 13. Warm Spring runs for 52 days, through June 3. High temperatures in this period are usually in the 50s, 60s and 70s. Warmer 80s and 90s occur infrequently. Memorial Day is in three days.