RodneyS

We did it again... Record lowest maximum tied at BWI today. That's four years in a row now. I wonder if there's a connection between climate change and cold outbreaks in October like this (I'm not saying there is, just speculating). Four years in a row and eight records broken or tied is significant.

We also shattered the low maximum record for October 8th at IAD by five degrees -- 51 today vs 56 in 2000. We just missed the record low maximum in DC, with a 55 degree reading at DCA. The DC record is 54, last recorded in 1910.

The way the first half of Oct. 2012 is looking per models, it would appear that it will likely be a good bit colder than 1991 fwiw. However, that would only put a fairly small dent in the +1.6. Nov. 1991 was quite chilly. So, it will be quite difficult for 11/2012 to be colder than that 11/1991. Now, Dec. 1991 was very warm. So, if we could get a cold Dec., rather big gains could be made then. Regardless, overcoming 1.6 F in Oct.-Dec. will be very tough.

I just calculated that for the average 2012 temperature at DCA to fall to 1991's average of 60.2 degrees would require a negative departure averaging four degrees in October, November, and December. That, in turn, would make those three months the 22nd coldest fourth quarter of all time in DC, and the coldest since 1989, which featured a December that averaged 27.9 degrees -- tied for the second coldest all-time.

To further update, January-August 2012 checks in at an average 64.1 degrees, breaking the 1991 first eight months record by 1.6 degrees.

The beat goes on: January-September 2012 checks in at an average 65.0 degrees, breaking the 1991 first nine months record by 1.6 degrees.

And January-July 2012 checks in at an average 61.7 degrees, breaking the 1991 first seven months record by 1.7 degrees.

To further update, January-August 2012 checks in at an average 64.1 degrees, breaking the 1991 first eight months record by 1.6 degrees.

Added 2nd warmest July/month.

And January-July 2012 checks in at an average 61.7 degrees, breaking the 1991 first seven months record by 1.7 degrees.

Not exactly breaking news, but the DCA 2012 First Half average temperature of 58.0 degrees easily broke the previous DC record of 56.4 set in 1991. June 2012 finished at 76.2, placing it in a tie for 23rd warmest on the all-time list. First Half precipitation, on the other hand, was the 7th lowest all-time, at only 13.12 inches. June 2012 finished at 2.38 inches, marking the 6th consecutive month of below normal precipitation at DCA.

Rodney, I noticed that LWX updated their monthly temperature numbers at http://www.erh.noaa....ca/dcatemps.txt

It now has 1944 as 71.6. My old spreadsheet placed us third, but with the update it looks like this May was 4th.

Thanks. 71.6 for May 1944 is indeed consistent with the daily figures that I have for that month. I would guess that the difference between the old 70.8 figure and the new 71.6 figure for May 1944 is the difference between using the old Weather Bureau at 24th and M Streets NW or (Reagan) National Airport for the official numbers. Weather records have been kept at National Airport since July 1, 1942, but the last I knew it was not the official source until July 1, 1945. Has that now changed?

Added hottest spring ever record (which we've already clinched). May will be somewhere in the top 10, but the exact placement depends upon the overall temp departure for today.

I wonder if Mattie g or Ellinwood will ever admit I was right. Probably not... LOL

I think things are now finalized: May 2012 in DC checks in with an average temperature of 71.4 degrees, third on the all-time list behind 1991 (73.0) and 2004 (71.8). However, spring (March-May) 2012 easily shatters the all-time record, with an average temperature of 62.2 degrees, beating the 1977 record of 60.7 degrees by 1.5 degrees. Further, the first five months of 2012 averaged 54.3 degrees, beating the 1991 record of 52.3 degrees by 2.0 degrees. Finally, the most recent 12 months (June 2011 to May 2012) averaged 61.8 degrees, beating the two-month-old warmest 12 consecutive months record of 61.6 degrees set during April 2011 to March 2012.

So basically what RodneyS is saying is that averages tend to...well...average out the peaks and valleys we can sometimes get.

At least for the last decade in DC. However, precipitation at DCA was below the 1871-2011 DC averages 12 out of 14 months during August 2001 to September 2002, with only 27.70 inches recorded during that period, versus an 1871-2011 average amount for those 14 months of 48.59 inches -- a deficit of 20.89 inches, or 43%. Further, there was a more significant drought in DC during November 1929 to April 1931. During those 18 consecutive months, precipitation was below the 1871-2011 averages in each month. During that period, a total of only 34.85 inches of precipitation were recorded, versus an 1871-2011 average amount of 59.29 inches -- a deficit of 24.44 inches, or 41%.

Added warmest Jan-Mar

2012: 47.3

1990: 46.3

1998: 44.4

Almost a clear 3 degrees above 3rd place. If we are merely average for the remainder of the year, we will have a top-5 warmest year at DCA. +0.7 the rest of the way makes 2012 the king. That is how warm it has been.

And now the warmest January-April average:

2012: 50.0

1990: 49.0

1976: 48.0

On the other hand, the March-April temperature increase of 1.5 degrees at DCA was the second smallest change on record in DC history and the smallest since 1907, when the temperature actually declined by 0.4 degrees between March and April. Also, assuming no rain before midnight at DCA, January-April 2012 precipitation will be only 7.46 inches -- the sixth lowest on record and the lowest since 1985's 7.09 inches. The all-time low was 6.28 inches in 1872. But then again, if you measure precipitation at DCA over the last nine months, it is 35.69 inches -- the 19th most on record from August to April. The record for those nine months was 44.88 inches from August 1934 to April 1935.

It's also worth noting that March 2012 was the third largest temperature anomaly relative to monthly historical DC averages, which date to 1871. The champ is still January 1950, which at 48.0 degrees was 12.8 degrees above the 1871-2012 January average of 35.2 degrees. Second is still February 1934, which at 24.6 degrees was 12.3 degrees below the 1871-2012 February average of 36.9 degrees. March 2012 checked in at 56.8 degrees, or 11.8 degrees above the 1871-2012 March average of 45.0 degrees. In doing so, it displaced January 1932 as third on the all-time list. January 1932 averaged 46.8 degrees, or 11.6 degrees above the 1871-2012 January average of 35.2 degrees.

Wouldn't it be special if either BWI, DCA, or LWX set a record for the earliest

100 degree record in modern times this year?

DCA and BWI, June 05, 1925.

That's a good one (although I don't think those airports existed then -- the temperatures were for the official measuring points in DC and Baltimore). I remember May 31,1991, when we almost broke the DC record for the earliest 100 degree reading, but came up a degree short.

An amazing record.

March 2012's mean temperature of 56.8° demolished the old record of 55.5° set in 1921 and tied in 1945. It was also almost 3.9 standard deviations above the 1981-2010 mean temperature for March. 3.9 standard deviation events have a statistical probability of occurring once every nearly 330 years.

I think a while back NOAA corrected the March 1945 average to 56.2, but we still broke the record.

And at least a dozen more somewhat obscure high average temperature records -- for the 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months ending in March 2012, as well as the warmest 12 consecutive months irrespective of ending month. I believe that the March 2012 number is now finalized at 56.8 degrees, beating the 1945 record by 0.6 degrees. Additionally: February-March 2012 averaged 50.6* degrees, beating the 1976 record by 1.5; January-March 2012 averaged 47.3 degrees, beating the 1990 record by 1.0; December 2011-March 2012 averaged 46.7 degrees, beating the 2001/2002 record by 2.3; November 2011-March 2012 averaged 47.9 degrees, beating the 2001/2002 record by 1.5; October 2011-March 2012 averaged 49.6 degrees, beating the 2001/2002 record by 0.9; September 2011-March 2012 averaged 52.7 degrees, beating the 1931/1932 record by 0.8; August 2011-March 2012 averaged 56.1 degrees, beating the 1973/1974 record by 0.8; July 2011-March 2012 averaged 59.3 degrees, beating the 1973/1974 record by 1.4; June 2011-March 2012 averaged 61.2 degrees, beating the 1973/1974 record by 1.3; May 2011-March 2012 averaged 61.9 degrees, beating the 2007/2008 record by 1.5; and April 2011-March 2012 averaged 61.6 degrees, beating the 1980/1981 record by 1.7. The last record is particularly noteworthy, because it is also the highest temperature for any 12-month period in DC history, beating the October 1990-September 1991 record by 0.8. Of course, this new 12-month record may be short-lived, if the April 2012 average temperature exceeds the April 2011 average of 58.8 degrees.

* Averages for more than one month (such as December, January, and February -- the three months of meteorological winter) have traditionally been calculated by assuming that each month has the same number of days, even though that method is slightly inaccurate because the months differ in length. For example, to calculate a true February-March 2012 average, the average temperature for each of those 60 days (29 in February and 31 in March) should be summed and divided by 60, rather than simply adding the average February temperature to the average March temperature and dividing by two. The true average for February-March 2012 is 50.8, rather than 50.6, but for consistency with traditional calculations, I have used the simpler method. Either way you do the calculations, all the above records were broken.

Correcting (in bold) a few figures above, as March finished at 56.8, and not 56.7.

Added warmest March on record.

And at least a dozen more somewhat obscure high average temperature records -- for the 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months ending in March 2012, as well as the warmest 12 consecutive months irrespective of ending month. I believe that the March 2012 number is now finalized at 56.7 degrees, beating the 1945 record by 0.5 degrees. Additionally: February-March 2012 averaged 50.5* degrees, beating the 1976 record by 1.4; January-March 2012 averaged 47.2 degrees, beating the 1990 record by 0.9; December 2011-March 2012 averaged 46.7 degrees, beating the 2001/2002 record by 2.3; November 2011-March 2012 averaged 47.8 degrees, beating the 2001/2002 record by 1.4; October 2011-March 2012 averaged 49.6 degrees, beating the 2001/2002 record by 0.9; September 2011-March 2012 averaged 52.7 degrees, beating the 1931/1932 record by 0.8; August 2011-March 2012 averaged 56.1 degrees, beating the 1973/1974 record by 0.8; July 2011-March 2012 averaged 59.3 degrees, beating the 1973/1974 record by 1.4; June 2011-March 2012 averaged 61.2 degrees, beating the 1973/1974 record by 1.3; May 2011-March 2012 averaged 61.9 degrees, beating the 2007/2008 record by 1.5; and April 2011-March 2012 averaged 61.6 degrees, beating the 1980/1981 record by 1.7. The last record is particularly noteworthy, because it is also the highest temperature for any 12-month period in DC history, beating the October 1990-September 1991 record by 0.8. Of course, this new 12-month record may be short-lived, if the April 2012 average temperature exceeds the April 2011 average of 58.8 degrees.

* Averages for more than one month (such as December, January, and February -- the three months of meteorological winter) have traditionally been calculated by assuming that each month has the same number of days, even though that method is slightly inaccurate because the months differ in length. For example, to calculate a true February-March 2012 average, the average temperature for each of those 60 days (29 in February and 31 in March) should be summed and divided by 60, rather than simply adding the average February temperature to the average March temperature and dividing by two. The true average for February-March 2012 is 50.8, rather than 50.5, but for consistency with traditional calculations, I have used the simpler method. Either way you do the calculations, all the above records were broken.

Also, I have a feeling that this is one of the top five warmest astronomical winter periods ever for BWI- does anyone know where it ranks?

I don't have Baltimore data, but regarding DC, I stated on this thread -- http://www.americanw...h-on-record-dca -- "We are also locked in to the warmest astronomical winter (approximately December 21st to March 20th each season) and the warmest composite meteorological/astronomical winter (December 1st to March 20th each season). Each of these two measures of winter currently (through March 13th) show average temperatures of 44.4 degrees in DC, versus the previous astronomical winter record of 43.7 in 1989-90 and the previous composite winter record of 44.0 in 2001-02"

The final figures in DC for both the 2011/12 astronomical and composite winters will be at least a degree higher than they were through March 13th -- I'll post them later today or early tomorrow on the above thread. Given by how much the DC records are going to be broken, I think it's pretty certain that the corresponding Baltimore records will also be broken.

5th wettest Sept (2011)

I would throw in 10th wettest August (2011), which when combined with September 2011, produced the third wettest August-September.

140 years is a big enough sample to seriously consider something other than coincidence at work. While I can't come up with a reasonable explanation for your data, nothing can be dismissed as a possible cause. Pure luck would make this a decent mathematical anomaly.

Do you have data on rainfall days during these times? It is also possible that a few Tropical systems are significantly skewing the averages.

August 12 has seen a trace of precipitation on 20 days, measurable precipitation on 51 days, at least an inch on 11 days, and at least two inches on 5 days; August 15 has seen a trace of precipitation on 15 days, measurable precipitation on 45 days, at least an inch on 4 days, and has never received two inches.

I was recently given historical weather data for Washington, DC. The data are very interesting in a number of respects, but I noted something particularly odd about two days in August that are only three days apart: During the period of record, 1871-2010, rainfall on August 12th has exceeded rainfall on August 15th by a factor of 3.7 -- 40.95 inches vs. 11.12 inches. Further, the differences have been quite consistent over the years. For example, consider these figures for 30-year periods (20 years for the most recent data):

1871-1900: 9.07 inches total on the 12th, 3.73 inches on the 15th.

1901-1930: 11.90 inches total on the 12th, 0.85 inches on the 15th.

1931-1960: 12.22 inches total on the 12th, 4.31 inches on the 15th.

1961-1990: 2.16 inches total on the 12th, 1.60 inches on the 15th.

1991-2010: 5.60 inches total on the 12th, 0.63 inches on the 15th.

August 15th has never had more than 1.15 inches of precipitation, while August 12th has exceeded that amount nine times, and has exceeded two inches five times. In fact, two of the largest rainfalls in Washington, DC history occurred on the 12th -- 4.92 inches in 1898 and 5.44 inches in 1955.

Is this just a random variation, or is there something more to it? In searching for an explanation, I came across this article on-line -- http://www.atmos.was...eteors_1956.pdf. That article suggests that there could be a correlation between rainfall and meteor showers -- specifically that rainfall peaks may occur about 30 days after meteor showers. While this hypothesis would not seem to directly relate to the difference in rainfall between August 12th and August 15th in Washington, DC, I find it interesting that more than 55 years ago a meteorologist was suggesting a correlation between rainfall and meteor showers.

So, does anyone have any insight into this matter? For example, are there other areas where there are significant variations in rainfall on different days only a few days apart? If so, is there any evidence that meteor showers could play a role? Thanks.