March 31: ORD

Today is March 31st. It's the 91st day of the year. 275 days remain. It's week 13 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. 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 53 and the normal low is 34. I've calculated the 33-year averages at 55 and 35.

On the warm side, in 1986 (O'Hare's warmest March 31st) the high was 83 with a low of 48, a 35 degree spread. Five years earlier, in 1981, the high was the record high of 87 with a low of 41, a HUGE 46 degree spread. Two years ago, in 2010, the high was 77 with a low of 51. In 1999 the high was 71 with a low of 48. In the prior year of 1998, the high was 72 with a low of 45. In 2006 the high was 68 with a low of 45. The other warm low was 46 in 1982. The record warmest low of 60 was set in 1967 at Midway. 22 of the past 33 highs (67%) were in the: 40s (12) and 50s (10). O'Hare recorded eight consecutive 40s & 50s highs from 1990 through 1997. On the warm side, ten highs (30%) were in the: 60s (5), 70s (3) and 80s (2). Prior to 1979, O'Hare's warm highs were 78 in 1978, 74 in 1971, 68 in 1967 and 65 in 1968. O'Hare's warmest low was 58 in 1967. On the cold side, one high in the past 33 years (3%) was in the 30s. 

In looking back through the years to the first March at O'Hare in 1959, the following instances were notable: In 1978 the high was a warm 78 with a low of 39, a 39 degree spread and warm day. In 1975 the high was 58 with a low of 24, a 34 degree spread. In 1971 the high was a warm 74 with a low of 42, a 32 degree spread and warm day. In 1969 the high was 33 with a low of 12, a cold day. 1969 was also the year of the record low (12 at Midway). In 1968 the high was a warm 65 degrees. In 1967 the high was 68 with a low of 58, another warm day and year of the record warmest low of 60 at Midway. In 1966 the high was 54 with a cold low of 22, a 32 degree spread. In 1964 the high was 35 with a low of 19, a cold day. In 1963 the low was a warm 46 degrees. In 1960 the high was was a cold 38 with a low of 31, a seven degree spread.

More recently, we had a small spread of seven degrees in 1990 (45/38). There were large spreads of 31 degrees in 2003 (55/24) and 37 degrees in 2000 (63/26).

On the cold side, in 1987 the high was 40 with a low of 20. Two years later, in 1989, the high was 37 with a low of 33, a four degree spread. The record low of 12 originally occurred in 1923 and was later tied in 1969. The record coldest high of 21 occurred in 1923. As you can see, 1923 was the coldest March 31st. Official readings in 1923 were taken adjacent to Lake Michigan. 17 of the last 33 lows (52%) were in the 30s. O'Hare recorded six consecutive 30s lows from 1988 through 1993. Eight lows (24%) were in the cold 20s. O'Hare's coldest March 31st was in 1969 with a high of 33 (coldest high of the date) and low of 12 (coldest low of the date). The second coldest was in 1964 with a high of 35 and low of 19. These two lows in the 10s (a.k.a. teens) were the only ones in O'Hare's history for the date. Eight lows (24%) were in the warm: 40s (7) and 50s (1). The only 50s low of the last 33 years (51 degrees) occurred two years ago in 2010. This was just the second 50s low in O'Hare's history for March 31st. The other was 58 in 1967.  


There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1986 the high was 83 with a low of 48, overall 22.5 degrees ABOVE normal. Then in 1987 the high was 40 with a low of 20, overall 13 degrees BELOW normal. 

Today is a major day in Chicago's snow history. Today and yesterday, back in 1926 at the University of Chicago, 8.7 inches fell. Rockford today had 13.5 of it's 16 inch total back in 1926.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:09 and sunrise is at 6:37. Sunset is at 19:19 and twilight ends at 19:47. There's a total of 12 hours, 42 minutes of daylight today and 13 hours, 38 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:07 and sunrise is at 6:35. The moon is waxing gibbous, having reached first quarter yesterday at 14:41. Illumination was 54% at midnight, will be 59% at noon and 64% at midnight tonight. Moonset was at 2:40 this morning. Moonrise is at 12:40 this afternoon. Moonset is at 3:18 tomorrow morning. Moonlight time is 14 hours which is 20 minutes shorter than yesterday.

Spring began on March 12th and runs for 84 days through June 3rd. Cool Spring began on March 12th and runs for 32 days through April 12th. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 60s and 70s usually occur infrequently. April Fools' Day and Palm Sunday are tomorrow. Good Friday is in six days. Easter is in eight days.