RodneyS

I don't have monthly minimum/maximum temperatures at Dulles at my fingertips, but I'll try and dig some out. I do know that some recent months have not featured such extreme minimum and maximum temperature differentials between the two airports. For example, in September 2011 the high temperature differential was 0.8 degrees and the low temperature differential was 3.6 degrees. Still 2.8 degrees greater on the low side, but that compares with 3.8 degrees greater on the low side this September.

The beat goes on -- September 2014 averaged 73.9 degrees at DCA (2.9 degrees above the 1981-2010 normal), but only 67.5 at IAD (0.4 degrees below the 1981-2010 normal). The 6.4 degree monthly differential is the greatest since that same differential in January 1984.

With respect to overall temperatures, the 2014 astronomical summer at DCA was a virtual carbon copy of 2013, averaging a minimum of 69.5 degrees and a maximum of 85.8 degrees. And, believe it or not, the overall average was identical no matter how many decimal points you carry it out -- 77.66 degrees to two decimal points, which is the 26th warmest in DC history.

I believe that was just three years ago -- July 19-25, 2011 averaged 89.2 degrees at DCA, making it also the hottest week ever in DC history. July 2-8, 2012 gave that week a good run for its money, averaging 89.1 degrees. July 7, 2012 featured DC's hottest average daily temperature ever at 93.5 degrees, with a high of 105 and a low of 82.

Also, the week of August 31-September 6 was the hottest seven consecutive day period of the year at DCA, averaging 84.7 degrees. During the 2014 meteorological summer, the hottest week was June 27-July 3, which averaged just 81.8 degrees. Eyeballing historical DC temperature records to determine which year had the latest hottest week, 1985 may be the champion. September 4-10, 1985 averaged 84.3 degrees, which was hotter than the hottest meteorological summer week of August 10-16, 1985, at 82.6 degrees. Also, in 1881, which is not only the hottest September in DC history, but also the only year in which September was the hottest month of the year in DC, September 3-9, 1881 averaged 82.8 degrees, which was slightly hotter than the hottest meteorological summer week of July 10-16, 1881, at 82.6 degrees.

Remarkable August 2014 temperature differential between DCA and IAD. DCA averaged 77.7 degrees -- warmer than last August and only the 22nd coldest August there since 1963, when records began at Dulles. IAD, on the other hand, averaged just 71.8 degrees -- the coldest since the record of 70.4 in August 1992, and the third coldest August ever there. The 5.9 degree August 2014 differential between the airports was the greatest since that same differential in October 1997. The greatest monthly differential between the airports was December 1975, at 7.3 degrees.

I have data for DC only -- that's where the aspiring Ph.D meteorology student or meteorology professor comes in. But you're right -- if meteor dust is involved, one would think it would be a worldwide phenomenon. And if there is a bona fide connection, maybe there actually could be some merit in those weather planning services that advise folks six months or a year in advance as to the best day to hold an outdoor wedding: "Stay away from August 12th in the mid-Atlantic unless you have an ample supply of rafts for the reception."

This 1956 article -- http://www.atmos.was...eteors_1956.pdf -- states: "The rainfall peaks occur approximately 30 days after meteor showers, and it is suggested that they are due to the nucleating effect of meteoric dust falling into cloud systems in the lower atmosphere, the time difference being accounted for by the rate of fall of the material through the atmosphere." The 30-day time frame does not work for the Perseid meteor shower and August 12th and 15th rainfall in DC, but perhaps some aspiring Ph.D meteorology student or meteorology professor can look into this general theory with 21st Century technology at his/her disposal. The effect could be more complex than the author of the above article envisioned; for example, perhaps a series of events has to occur, and then a meteor shower can trigger a significant rain event.

Time for an update. With yesterday's 1.60 inches of rain at DCA, August 12th rainfall there during 1991-2014 totals 7.20 inches, vs just 0.63 inches on August 15th during 1991-2013 (and the strong likelihood of a dry day this Friday, the 15th). So, the historical rainfall totals for these two days, 1871-2014 in DC, are: August 12th: 42.55 inches vs August 15th: 11.12 inches. The rainiest August 15th in DC history would rank as just the 11th rainiest on August 12th. Coincidence, or does the annual Perseid meteor shower have something to do with it?

This temperature differential to this point in the year is the 4th greatest between the two airports. The greatest was 6.6 in 1976, followed by 5.33 in 1981, and 5.26 in 1975. The smallest was 1.4 in 2009. For the year as a whole, the greatest was 5.9 in 1976 and the smallest was 1.7 in 2009.

DCA is an outlier for the mid-Atlantic, with a 2014 average monthly departure from the 1981-2010 January-July normals of only -0.6 degrees. IAD's average monthly departure is -2.9 degrees.

The first seven months at DCA this year averaged 56.5 degrees -- 5.1 degrees higher than IAD. That makes January-July 2014 at DCA only the 20th coldest during the 52 years of IAD's existence. In fact, the coldest first seven months at DCA during that period was just 11 years ago -- 2003 averaged 54.0 degrees there.

Pretty ho-hum historical average July 2014 temperature at DCA at just 0.4 degrees below the 1981-2010 normal. IAD, however, was 2.5 degrees below that normal, and for the first seven months of the year its average temperature is 51.4 degrees -- fifth coldest of 52 years, and the coldest since 1984. 1970 was the coldest first seven months at IAD, averaging 50.5 degrees.

BWI got down to 55 this morning (July 30th) to beat the old record low by a degree. Dulles made it all the way down to 48 this morning to beat the old record low by 3 degrees.

Quite an historical contrast in June 2014 average minimum and maximum temperatures at DCA. The average minimum was 68.8 degrees, good enough for 6th warmest on the all-time DC list. The average maximum, on the other hand, was 85.6 degrees, tied for only 31st warmest on the all-time DC list. In June 1994, DCA recorded an average maximum of 90.0 degrees, the all-time DC high for June -- 4.4 degrees higher than this year. However, the average DCA minimum in June 1994 was only 68.7 degrees, 0.1 lower than this year.

IAD missed tying by a degree at 59 degrees -- record for May 29th there still stands at 58, also set in 1996. DC record for May 29th is 58, set in 1893; and DCA record is 60, also set in 1996. DCA recorded a maximum of 62 yesterday.

Is he talking about below the 1981-2010 normals? If so, I think that may be true with an asterisk. I haven't checked every year, but I know that in 1996 at BWI July, August, October, and November were all below normal, with September exactly at normal. So, that would be five consecutive months of normal and below, but only four of the five below. At IAD, I believe that the last year with four consecutive below normal months was 2000, when June-September were all below.

The temperature at IAD last night rose four degrees after I posted the above to peak at 58 right before midnight, causing April's average to tick up from 52.1 to 52.2, and the first four months average to tick up to 37.25. That is still the third coldest first third of the year ever at IAD, and the coldest April (tied with 2007) since 50.3 was recorded in 1997.

Same deal for January-April. The first four months of 2014 at IAD averaged 37.23 degrees, beaten for the coldest first third of the year only by 1970 at 36.73 and 1978 at 37.20.

Jan-Mar 2014 was third coldest (of 52 years) at IAD, with an average temperature of 32.27 degrees. Coldest was 1970, with an average of 31.47; and second coldest was 1978, with an average of 31.53.

I agree. DCA, on the other hand, was a not terribly cold 42.9 -- the coldest only since 1996, which also averaged 42.9.

It may have occurred to most in this area that March 2014 was a rather up and down month. How up and down? Since official daily temperature records began in DC in January 1872, there have now been a total of 1707 months recorded, listing the minimum and maximum temperature for each day of each month. According to my figures, with respect to the average daily change in maximum temperature, March 2014 month was -- drum roll, please -- number one! That's correct, with an average daily change in the maximum temperature of 12.4 degrees at DCA, March 2014 displaced long-time record-holder February 1900 (12.1). Also, with respect to the average daily change in the mean temperature, March 2014 was number three, at 9.1 degree. January 1916 remains the record-holder in that category, at 9.34 degrees, narrowly edging January 1950, at 9.32 degrees. Here are the top five months in each category: Average Daily Change in Maximum TemperatureMarch 2014, 12.4 February 1900, 12.1 March 1934, 11.9 March 1923, 11.71 February 1918, 11.68 Average Daily Change in Mean Temperature January 1916, 9.34 January 1950, 9.32 March 2014, 9.1 Febuary 1900, 8.8 March 1938, 8.7

True, and the March 2014 snow total at Dulles just increased to 19.8 inches. Also, the March 2014 snow total at Reagan is now 12.7 inches, which is the highest March total there since 1960. The respective IAD/DCA 2013-14 snow season totals are 52.8 and 32.0 inches, so the difference is a record-breaking 20.8 inches.

This season's astronomical winter averaged only 37.4 degrees at DCA, down 3.0 degrees from last year and 8.5 degrees below the record-setting pace of 2011-12. 2013-14 was the coldest astronomical winter at DCA since 2002-03 (35.8 degrees) and averaged slightly below the historical (1871 to the present) DC average of 37.7 degrees.

Thanks. In that case, the IAD/DCA snowfall separation for 2013-14 is 18.7 inches (49.0 vs 30.3), making this year #1 for separation.