RodneyS

I just posted this on the Capital Weather Gang board: " . . .11 straight days of measurable precipitation at DCA. .. According to my records, that sets the all-time DC record (back to 1871) for most consecutive days of measurable precipitation. I believe that the previous record was ten (twice: August 12-21, 1873 and July 17-26, 1938). During August 9-24, 1920, there were 16 straight days of at least a trace of precipitation, but only seven straight days of measurable."

Assuming that the temperature does not rise to 60 degrees before midnight, an all-time DC record will be set, with each day April 28-May 1 failing to reach 60.

Final three days of April with maximums in the 50s at DCA marked the first time for anything like that since 1966, when the final four days had maximums ranging between 46-59.

Dulles also recorded a low of 24 this morning, tying the record for April 6th set in 1966.

Yes. DCA averaged 53.5 degrees, which was 4th all time -- 3.3 degrees cooler than March 2012. IAD averaged 50.6 degrees, which was 2nd all time -- 3.7 degrees cooler than March 2012.

DCA astronomical (December 21-March 20) and composite (December 1-March 20) winters were even warmer, at 42.8 and 43.9 degrees, respectively. Those averages were good enough for a 5th place tie and 3rd place, respectively, all-time in DC. The comparable averages for 1997-98 were 42.5 and 42.4. The warmest astronomical and composite DC winters each occurred during a weak La Nina in 2011-12, at 45.9 and 45.6, respectively.

The temperature range at DCA that day was 7 to 32. So, the maximum was 3-degrees higher at IAD, but the minimum was 24-degrees lower. As previously mentioned on this thread, that is one of three times that there has been a 24-degree difference between the minimums at the two airports.

Not sure about Baltimore, but in DC the record one-day spread is 50 degrees -- March 22 1907, when the temperature range was 90/40.

Pretty interesting 2015-16 meteorological winter at DCA, as despite the blizzard and relative cold of January, the average temperature was 42.0 degrees -- good enough for an 8th place tie for warmest in DC history. The last Super El Nino, in 1997-98, was the 6th warmest DC winter at 42.4 degrees. However, that winter lacked the variability of this one, with a standard deviation from the average daily winter temperature of only 6.1 degrees, compared to 10.7 degrees this season. In fact, this winter at DCA had the highest standard deviation since the winter of 1989-90, which came in at 11.1 degrees.

It looks as if the IAD temperature peaked at about 52 this afternoon (and is now higher), so the afternoon difference between DCA and IAD was only about 13 degrees. To my surprise, I found that the greatest difference in the daily maximum temperature at the two airports is four degrees higher. That occurred on December 9, 1975, when DCA recorded a high of 53 and IAD 36. So, today did not come close to that, although there is still the question of the greatest difference at the same time. By the way, I found a third case of a 24-degree difference in the daily minimums, which occurred on February 13, 1983, when DCA recorded 16 degrees and IAD minus 8.

At 2:52 PM today, there was a temperature difference of 21 degrees between DCA (65) and IAD (44). Not a record, as on both January 21, 1984 and January 28, 1987, the daily DCA/IAD minimums differed by 24 degrees (8 and minus 16, and 7 and minus 17, respectively). However, both of those occurred with significant snow on the ground at IAD and a clear night, and so radiational cooling was the source of the extreme difference in morning lows. Does anyone know what the record is for the largest afternoon difference, both at the same time and for the entire afternoon? (IAD is still forecast to reach about 60 later today.)

And January wasn't cold. It was cool. However the 34.9 degree average temperature at DCA, while only 0.3 degrees below the January 1871-2016 DC average of 35.2 degrees, was 16.3 degrees below the December 2015 average DCA temperature of 51.2 degrees. That decline represented the greatest one-month change from December in DC history. The previous record-holder was January 1912, which declined 16.0 degrees from December 1911. (The largest increase was January 1990, which was up 15.7 degrees from December 1989.)

If you define subfreezing as 31 degrees and below, such a failure last happened at DCA four winters ago. During the winter of 2011-12 (Weak La Nina), the low maximum was 32 on January 22, 2012. The last winter at DCA in which the maximum exceeded 32 every day was the prior very strong El Nino in 1997-98, when the low maximum was 34 on March 11, 1998.

At DCA, it was no contest. The November-December 2015 average temperature there was 52.5 degrees, which broke the 2001 record by 2.3 degrees. In fact, starting in March 2015, I believe that DCA broke every composite DC monthly record ending in December 2015 -- ten records in all.

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.