RodneyS

When the DCA temperature sensor was replaced on August 10th, the psychro-dyne indicated that it was reading 1.7 degrees too high. From that date forward, the 2015 DCA-IAD average temperature differential shrunk from 5.06 degrees through August 9th to 3.45 degrees thereafter -- a reduction of 1.61 degrees. So, I think that's a pretty good indication that the old sensor was reading about 1.7 degrees too high for many months. If it was doing so beginning no later than New Year's Day 2015, the official yearly average temperature at DCA was inflated by a full degree by the faulty sensor. However, there have very likely been past sensor issues at many sites -- including DCA and IAD -- that received little attention or even went undetected. For example, in 1976, the DCA-IAD annual temperature differential was 5.9 degrees, whereas in 2009 it was only 1.7 degrees. Were the DCA and IAD sensors both accurate in those years? So, I think the bottom line is that there was a problem with the DCA sensor for much of 2015, but attempting to adjust the numbers would open up a new can of worms.

Impressive performance by Weather.com and AccuWeather in mid-December to pretty much nail the final December 2015 DCA average of 51.2. That was 11.5 degrees above normal. IAD, at 48.7, was 12.1 degrees above normal; and BWI, at 49.0, was 12.3 degrees above normal.

September 1881 was a pretty remarkable month, even though the average temperature of 78.2 was just 8.4 degrees above the 1871-2015 average of 69.8. For one thing, it was the warmest month of the year -- the only time in DC history that September has been warmer than June, July,and August. Second, the maximum was 104 on September 7th -- tied for the 6th highest maximum in DC history, with the top five all occurring much earlier (between July 7-August 17). It's also interesting to note that New Year's Day 1881 featured a minimum of minus 14 -- the second lowest in DC history. So, the 1881 DC temperature range was 118 degrees -- greatest yearly range in DC history.

For some reason, in the late 1880s there was a gap in recording December snow in DC, but in all of those years at least a trace of November snow was recorded. More recently, neither December 1972 nor December 1991 saw even a trace of snow at DCA, but traces were recorded there in November 1972 and November 1991.

And that season DCA recorded a trace on January 6th. Looking at the forecasts for next week, I would venture that record is about to fall. However, DCA did manage to record 3.2 inches of measurable snow after that in January and February, which was 0.6 inches more than IAD.

BWI definitely has a higher hurdle than DCA to break the all-time meteorological winter temperature average in 2015-16, and it won't be easy even at DCA. One thing I just noticed about both Baltimore and DC in 1931-32 is that March was colder than December-February. In Baltimore, March 1932 averaged only 40.3 degrees vs a low meteorological winter monthly temperature average of 42.8 in February, and in DC the comparable numbers were 40.0 in March and 42.9 in February.

The winter of 1931-32 is still the record-holder in DC, but I would not bet against this winter surpassing it. December 1931 came in at 44.2 degrees in DC vs an estimated 51.2 this year at DCA. January 1932 averaged 46.8 and February 1932 averaged 42.9 in DC, and so DCA will have to average about 41.4 in January-February 2016 to surpass the 1931-32 winter average temperature.

I think the best way to look at this may be to compute the historical (1871-2015) DC average temperature for each month, and then see how much each contending month deviates from that average. By that measure, December 2015 will be the champion, if 51.2 holds as the final average, as that would be 13.0 degrees above the historical December average of 38.2. The current champion is January 1950, with an average of 48.0 vs the historical January average of 35.2, for an anomaly of +12.8 degrees. On the minus side, the champion is February 1934, with an average of 24.6 vs the historical February average of 36.9, for an anomaly of -12.3 degrees.

Even with the temperature falling to 60 yesterday, DCA still established an-all time December record high minimum for DC, but fell short of the all-time meteorological winter high minimum of 61 established on February 16, 1891. IAD, on the other hand, with a December 24, 2015 minimum of 63 broke the all-time record meteorological winter high minimum of 62 established there on January 8, 1998.

I think you are correct for the average temperature in DC. Looking only at the maximum, I believe that January 26, 1950 has it, with a high of 79 -- 35.2 degrees above the current normal high of 43.8 for January 26th.

WDOR??? If you're asking whether DCA will bring the record for the warmest December in DC history, I would say it's about 95% certain, and about 75% that it will break the record for the warmest winter month in DC history.

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.