RodneyS

According to my records, the biggest gap is 1.8 degrees for both DC monthly all-time maximum and minimum average temperatures. October 2007 broke the maximum record with a 67.0 average temperature vs. 65.2 in October 1984. August 1927 broke the minimum record with a 70.0 average temperature vs. 71.8 in August 1903. By the way, weather.com currently shows forecasts that would bring the DCA December 2015 average to 50.4 degrees -- erasing the all-time high winter month average temperature of 48.0 set in January 1950.

Weather.com now has forecasts through December 30th, and they're even warmer: Average DC temperature Dec 1-30, 2015 = 51.3 degrees.

I just did the same thing with AccuWeather's DC projections and got 50.9 degrees. That would not only shatter the December record of 45.6 degrees set in 1889 and tied in 1984, but also the all-time winter monthly record of 48.0 degrees set in January 1950.

Yes, 6th warmest of 145 Novembers at 53.7 degrees. IAD was 3rd warmest of 53 Novembers at 50.3 degrees.

DCA did manage to tie the record high DC minimum for November 19th, at 59 degrees.

It did hold, and IAD's minimum yesterday exceeded DCA's by three degrees. The last time that IAD's minimum exceeded DCA's was, I believe, April 7th. IAD currently has a departure for November of +10.1 degrees, vs.+ 8.4 at DCA.

IAD also appears to have had a 63 minimum this morning, which would break the high minimum record of 61 set on this date in 2003, if it holds through midnight.

The same is true for DCA (including historical DC records back to 1872) and IAD, with the NWS forecasts for Friday (November 6th) being 80 and 79, respectively, and the current records in each case being 78. However, the hurdle is not all that great, as the record high temperature from Nov. 6th until the end of the year is 83 for DCA and 81 for IAD. Both of those records were set on November 15, 1993.

Whoops -- thanks. However, if the rain gauge were accurate at IAD . . . just kidding.

Yesterday's 1.65 inches of precipitation at DCA was the highest daily amount there only since June 27th's 2.75 inches; however, yesterday's 1.57 inches of precipitation at IAD was the highest daily amount there since June 8, 2014 (1.71 inches).

The 2015 DCA astronomical summer (June 21-Sept 23) averaged 79.21 degrees -- 5th warmest in DC history. Warmest was 1980, at 81.74 degrees. The 2015 DCA meteorological summer (June 1-Aug 31) was also 5th warmest in DC history, at 79.68 degrees. Warmest was 2010, at 81.24 degrees.

Didn't happen, as DCA recorded only 1.16 inches of precipitation in August, 15th lowest in DC history. Meteorological summer total of 18.11 inches still good enough for 13th all-time.

No precipitation on either day this year. Here is the summary precipitation table for the two days in DC, 1871-2015: August 12: 42.55 inches total; 21 days with a trace, 52 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 11.12 inches total; 16 days with a trace, 45 days with measurable, 4 days with at least an inch, no days with 2+ inches.

Similar picture for DCA, which has seen 16.95 inches of precipitation this meteorological summer, already # 17 on the all-time DC list. However, the DC summer record is a staggering 27.05 inches, set in 1906. But to make the Top 5, DCA needs just 2.94 inches in August.

DCA added 0.01 inches to finish at 11.94 inches for June 2015 (8th rainiest month in DC history), with last night's good-sized storm (0.97 inches) occurring entirely after midnight. The average June 2015 temperature at DCA was 78.1 degrees, a departure of +2.9, and the 6th warmest June in DC history. However, just five years ago, the all-time June record of 80.6 degrees was set at DCA, and so we were a long way from that.

With yesterday's record-breaking rainfall, June 2015 at DCA is now at 11.93 inches, which not only places the month second all-time in DC for June, but eighth overall. Here is the list of Top Ten rainiest months ever in DC, since official records began in 1871: September 1934: 17.45 inches August 1928: 14.41 inches August 1906: 14.36 inches August 1955: 14.31 inches June 2006: 14.02 inches August 1875: 12.93 inches September 1975: 12.36 inches June 2015: 11.93 inches August 1942: 11.61 inches June 1972: 11.53 inches

June 2015 at DCA is now up to 11.01 inches of precipitation, making it the third wettest June in DC history, and the 11th wettest of 1734 months overall.

Fifth all-time for June in DC. Here is the table: June 2006: 14.02 June 1972: 11.53 June 1900: 10.94 June 2013: 9.97 June 2015: 9.18 Second place is well within reach, but the record will be a challenge.

It's interesting to note how widely rainfall varies between Baltimore and DC. Here are the DC figure for those same months, with the DC surplus or deficit relative to Baltimore shown in parentheses: Aug 1955 - 14.31 (-4.04) Aug 1933 - 9.91 (-3.92) Sept 2011 - 8.84 (-4.48) Sept 1934 - 17.45 (5.04) Aug 1911 - 7.27 (-5.01) Sept 1999 - 10.27 (-1.23) Jul 1889 - 8.13 (-2.90) Aug 1971 - 7.18 (-3.73) Jul 1905 - 9.95 (-0.70) Sept 1876 - 10.81 (0.29) Aug 2011 - 8.92 (-1.46) So far this month, DCA has 9.18 inches, but that still leaves it 4.84 inches short of the June record of 14.02 inches, set just nine years ago, when BWI had just 7.32 inches. So, in June 2006, DCA had a 6.70 inch surplus relative to BWI.

DCA is in the same range, with 7.86 inches of precipitation so far in June, placing it 7th all-time, even if no more were to fall this month. However, it's still a long way from the record June total of 14.02 inches, set in 2006.

The ultimate in this context would be to have a warmer May than June in the same calendar year. The closest DC has ever come was 1918, at 69.6 degrees in May and 70.8 degrees in June.

I think perception of heat depends on whether you're focusing on average maximum or average minimum temperatures. This year at DCA, the average May minimum was 63.8 vs. 62.8 in 1991, and even at IAD the relative numbers for those two Mays are 57.5 vs 57.1. On the other hand, IAD has yet to record its first 90+ degree day of 2015, whereas in 1991 maximums for the last seven days of May ranged between 90 and 95. By the way, the warmest May at IAD was actually 2004 at 69.8, followed by 69.3 in 1991 and 68.9 in 2015.

Warmest average DC May temperature (73.2 at DCA, vs 73.0 in 1991). However, average maximum temp. of 82.4 was exceeded by 83.1 in 1991. Also, current precipitation (assuming none this evening) of 1.92 inches ranks as only the 28th driest in DC history -- 1991 was only 1.57 inches. 1991 also finished with these three maximum temperatures: 97 on May 29th, 98 on May 30th, and 99 on May 31st.

I'm not sure that any meteorological organization uses weighted averages. Presumably, that is because in the old days -- prior to the widespread use of calculators -- it was a pain to compute anything but unweighted averages by hand, and the methodology was never updated. In general, this isn't a big deal, but when you have an abnormally cold or warm February, unweighted averages can result in slightly erroneous figures for both the first quarter and the meteorological winter.

I agree with your figures (I previously misstated this year's 1Q at IAD as 31.6 degrees). Bear in mind, though that these figures are unweighted averages of January, February, and March average monthly temperatures, which gives too much weight to February, as it has only 28 days (29 in leap years), compared to 31 days each in January and March. Weighting each of the first 90 days of each year equally results in 1Q 1970 being colder than 1Q 1978 at IAD (31.4 vs. 31.7). 2015 would still be third coldest, but at 32.0 degrees, rather than 31.8. Perhaps some day weighted averages will be used to calculate quarterly and seasonal averages.