RodneyS

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.

The National Weather Service has upped DCA's snow accumulation for the March 16-17 storm from 6.7 to 7.7 inches, so now the IAD/DCA snowfall separation for 2013-14 is only 18.2 inches. So, for the moment at least, the 1992-93 snow season remains the kingpin for IAD/DCA snowfall separation, at 18.6 inches.

IAD has now recorded 16.0 inches of snow in March 2014, bringing the 2013-14 total to 49.0 inches vs. only 29.8 inches for DCA. Thus, the separation of 19.2 inches has now surpassed the previous record set in 1992-93.

I should have said "1.0 degrees below the 1981-2010 average of 38.4." For some reason, the normalization process shaves 0.2 degrees off the average at DCA, reducing the 1981-2010 meteorological winter normal there to 38.2 degrees. For purposes of comparing the current year with the baseline, I would argue that the average is a better measure to use, but perhaps some normalization guru can explain why I'm wrong. In any event, while the 2013-14 meteorological winter at DCA was 1.0 degrees below the 1981-2010 average, it was only 0.8 degrees below the 1981-2010 normal.

The same for IAD, except that today's minimum of -1 only tied the all-time low for March. The other time was after the 1993 "Storm of the Century," when -1 was recorded on March 15th.

I haven't checked every year in DC, but during the 1904-05 snow season, there were 21 days with measurable snow and 16 additional days with a trace of snow, for a total of 37 days on which at least a trace fell. During that same season, there was measurable snow on the ground on 55 days and a trace of snow on the ground on an additional 20 days, for a total of 75 days with at least a trace on the ground.

Another thing that marked the 2013-14 meteorological winter in this area was the average daily temperature change. At DCA, that average was 6.1 degrees, which was the highest since the 6.8 degree average daily change that occurred during the 1990-91 winter. However, 6.1 degrees is only tied for 31st all-time in DC. During the first 29 years of daily temperature records in DC (1872-1900), the average daily temperature change during the meteorological winter exceeded 6.1 degrees twelve times, including the all-time record of 7.6 degrees during the winter of 1889-90. That winter was also the second warmest in DC history, with an average temperature of 44.3 degrees vs 37.4 degrees this winter.

At IAD, it's tied for the 8th coldest so far out of 52 years, with a January-February average of 29.7 degrees vs a 1981-2010 normal of 34.7 degrees. It's interesting to note that the three coldest IAD first two months composites came back-to-back-to-back: 1977 (27.9), 1978 (27.0), and 1979 (27.25). In DC, it's tied for the 58th coldest so far out of 144 years, with a January-February average at DCA of 35.0 degrees vs a 1981-2010 normal of 37.5 degrees. The coldest DC first two months composite was 1904 (27.95), and the coldest DCA first two months composite was 1963 (31.2).