RodneyS Posted February 23, 2011 Share Posted February 23, 2011 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. Link to comment Share on other sites More sharing options...
AfewUniversesBelowNormal Posted February 23, 2011 Share Posted February 23, 2011 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. Link to comment Share on other sites More sharing options...
am19psu Posted February 23, 2011 Share Posted February 23, 2011 140 years is a big enough sample to seriously consider something other than coincidence at work. Not really. We're not given the full range of daily precip amounts or the autocorrelation between days. It could just as easily be well within the distribution. Link to comment Share on other sites More sharing options...
RodneyS Posted February 23, 2011 Author Share Posted February 23, 2011 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. Link to comment Share on other sites More sharing options...
RodneyS Posted August 13, 2014 Author Share Posted August 13, 2014 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. 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? Link to comment Share on other sites More sharing options...
RodneyS Posted August 13, 2014 Author Share Posted August 13, 2014 Highly doubt a meteor shower would cause the disparity. What would be your theory on that? 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. Link to comment Share on other sites More sharing options...
GramaxRefugee Posted August 13, 2014 Share Posted August 13, 2014 Do you have similar data for Baltimore? How about Richmond or Raleigh? My meaning....if it was meteor dust, as noted, it would not be confined to DC alone. Fascinating either way. 1 Link to comment Share on other sites More sharing options...
RodneyS Posted August 13, 2014 Author Share Posted August 13, 2014 Do you have similar data for Baltimore? How about Richmond or Raleigh? My meaning....if it was meteor dust, as noted, it would not be confined to DC alone. Fascinating either way. I have data for DC only -- that's where the aspiring Ph.D meteorology student or meteorology professor comes in. But you're right -- if meteor dust is involved, one would think it would be a worldwide phenomenon. And if there is a bona fide connection, maybe there actually could be some merit in those weather planning services that advise folks six months or a year in advance as to the best day to hold an outdoor wedding: "Stay away from August 12th in the mid-Atlantic unless you have an ample supply of rafts for the reception." Link to comment Share on other sites More sharing options...
RodneyS Posted August 17, 2015 Author Share Posted August 17, 2015 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? 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. Link to comment Share on other sites More sharing options...
RodneyS Posted August 16, 2016 Author Share Posted August 16, 2016 On 8/17/2015 at 9:25 AM, RodneyS said: 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. At last, a rainy August 15th at DCA (1.16 inches) and nothing on the 12th. Here are the updated totals, 1871-2016: 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: 12.28 inches total; 16 days with a trace, 46 days with measurable, 5 days with at least an inch, no days with 2+ inches. Link to comment Share on other sites More sharing options...
wxdude64 Posted August 16, 2016 Share Posted August 16, 2016 58 minutes ago, RodneyS said: At last, a rainy August 15th at DCA (1.16 inches) and nothing on the 12th. Here are the updated totals, 1871-2016: 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: 12.28 inches total; 16 days with a trace, 46 days with measurable, 5 days with at least an inch, no days with 2+ inches. So, from your original post yesterday set a new rainfall record for the 15th for DC? "August 15th has never had more than 1.15 inches of precipitation" Link to comment Share on other sites More sharing options...
MN Transplant Posted August 16, 2016 Share Posted August 16, 2016 10 minutes ago, wxdude64 said: So, from your original post yesterday set a new rainfall record for the 15th for DC? "August 15th has never had more than 1.15 inches of precipitation" RECORD EVENT REPORT NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 0122 AM EDT TUE AUG 16 2016 ...RECORD DAILY MAXIMUM RAINFALL SET AT WASHINGTON NATIONAL DC... A RECORD RAINFALL OF 1.16 INCHES WAS SET AT WASHINGTON NATIONAL DC YESTERDAY. THIS BREAKS THE OLD RECORD OF 1.15 SET IN 1941. Link to comment Share on other sites More sharing options...
RodneyS Posted August 16, 2016 Author Share Posted August 16, 2016 4 minutes ago, wxdude64 said: So, from your original post yesterday set a new rainfall record for the 15th for DC? "August 15th has never had more than 1.15 inches of precipitation" Yes indeed, good observation -- yesterday was the rainiest August 15th ever in DC. However, 1.16 inches on August 12th would rank as only the 11th rainiest for that day of the year, and so there is still quite a discrepancy between August 12th and August 15th in DC historically. I'm still waiting for some aspiring meterorologist to write his/her Ph.D thesis on this subject. Link to comment Share on other sites More sharing options...
RodneyS Posted August 16, 2017 Author Share Posted August 16, 2017 On 8/16/2016 at 8:37 AM, RodneyS said: At last, a rainy August 15th at DCA (1.16 inches) and nothing on the 12th. Here are the updated totals, 1871-2016: 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: 12.28 inches total; 16 days with a trace, 46 days with measurable, 5 days with at least an inch, no days with 2+ inches. This year featured rain on each day, with DCA recording 0.52 inches on August 12th and 0.17 inches on August 15th. So the updated totals, 1871-2017, are: August 12: 43.07 inches total; 21 days with a trace, 53 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.45 inches total; 16 days with a trace, 47 days with measurable, 5 days with at least an inch, no days with 2+ inches. Link to comment Share on other sites More sharing options...
GramaxRefugee Posted August 16, 2017 Share Posted August 16, 2017 So, a factor of 3 difference. Not far off the pace really. Link to comment Share on other sites More sharing options...
RodneyS Posted August 16, 2017 Author Share Posted August 16, 2017 12 hours ago, GramaxRefugee said: So, a factor of 3 difference. Not far off the pace really. Right, although yesterday there were much higher rain totals not far from DCA. Still, I find it interesting that since I began this thread six and a half years ago, the same general pattern that existed for these two days prior to August 2011 has continued, albeit to a lesser extent; i.e., August 12th continues to be rainier than August 15th. Specifically, in the last seven years DCA has recorded 2.12 inches of precipitation on the 12th, but only 1.33 inches on the 15th. A very long-term coincidence, or something more? Link to comment Share on other sites More sharing options...
RodneyS Posted August 17, 2018 Author Share Posted August 17, 2018 On 8/15/2017 at 8:47 PM, RodneyS said: This year featured rain on each day, with DCA recording 0.52 inches on August 12th and 0.17 inches on August 15th. So the updated totals, 1871-2017, are: August 12: 43.07 inches total; 21 days with a trace, 53 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.45 inches total; 16 days with a trace, 47 days with measurable, 5 days with at least an inch, no days with 2+ inches. The beat goes on. This year, DCA recorded 0.36 inches of precipitation on August 12th and nothing on August 15th. So, the updated totals, 1871-2018, are: August 12: 43.43 inches total; 21 days with a trace, 54 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.45 inches total; 16 days with a trace, 47 days with measurable, 5 days with at least an inch, no days with 2+ inches. 4 Link to comment Share on other sites More sharing options...
RodneyS Posted August 17, 2020 Author Share Posted August 17, 2020 On 8/16/2018 at 9:36 PM, RodneyS said: The beat goes on. This year, DCA recorded 0.36 inches of precipitation on August 12th and nothing on August 15th. So, the updated totals, 1871-2018, are: August 12: 43.43 inches total; 21 days with a trace, 54 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.45 inches total; 16 days with a trace, 47 days with measurable, 5 days with at least an inch, no days with 2+ inches. Time for an update. Not much has happened to change the picture during the last two years. In 2019, August 12th had no precipitation at DCA, whereas August 15th had 0.20 inches. This year, August 12th had 0.26, whereas August 15th had 0.21. So the updated 150-year totals for DC, 1871-2020, are: August 12: 43.69 inches total; 21 days with a trace, 55 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.86 inches total; 16 days with a trace, 49 days with measurable, 5 days with at least an inch, no days with 2+ inches. 6 Link to comment Share on other sites More sharing options...
RodneyS Posted August 17, 2023 Author Share Posted August 17, 2023 On 8/16/2020 at 8:16 PM, RodneyS said: Time for an update. Not much has happened to change the picture during the last two years. In 2019, August 12th had no precipitation at DCA, whereas August 15th had 0.20 inches. This year, August 12th had 0.26, whereas August 15th had 0.21. So the updated 150-year totals for DC, 1871-2020, are: August 12: 43.69 inches total; 21 days with a trace, 55 days with measurable, 12 days with at least an inch, 5 days with 2+ inches. August 15: 12.86 inches total; 16 days with a trace, 49 days with measurable, 5 days with at least an inch, no days with 2+ inches. Time for another update. Rainfall at DCA on August 12th has gone missing recently, as the last three years have totaled zero, a trace, and zero. On the other hand, rainfall the last three years on August 15th has totaled 0.24, 0.01, and 0.38 inches. However, no major storms have occurred on August 15th, and so the Top 10 rainiest days in DC history on August 12th or 15th remain entirely on August 12th. In the 13 years since I began tracking the difference in official DC precipitation on these two days, the major disparity that I found during 1871-2010 had not continued, which might suggest that disparity was an aberration. However, 13 years is too short a time period to conclude that, especially since August 12th has continued to be slightly wetter than August 15th, even though August 15th has recorded a few more rainy days during that recent period. Specifically, here are the 2011-2023 precipitation numbers for the two days at DCA: August 12: 2.74 inches total; 2 days with a trace, 4 days with measurable, 1 day with at least an inch, no days with 2+ inches. August 15: 2.37 inches total; 1 day with a trace, 7 days with measurable, 1 day with at least an inch, no days with 2+ inches. This is in contrast to the 1871-2010 precipitation numbers for the two days in DC: August 12: 40.95 inches total; 20 days with a trace, 51 days with measurable, 11 days with at least an inch, 5 days with 2+ inches. August 15: 11.12 inches total; 15 days with a trace, 45 days with measurable, 4 days with at least an inch, no days with 2+ inches. 4 2 Link to comment Share on other sites More sharing options...
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