Rainy Weekends Not a Myth in 2019 in This Area

[RodneyS]

Most of us have complained at some point about rainy days seeming to occur more often on weekends than on weekdays.  However, as the Capital Weather Gang recently noted, that has actually been the case this year in this area, assuming that the weekend is defined to include Friday; see https://www.washingtonpost.com/weather/2019/05/13/washingtons-wettest-days-history-inches-precipitation-have-fallen-past-year/?utm_term=.2bb2b4bf05c4.  Specifically, through the first 19 weeks of 2019 at DCA, there have been 32 weekend days on which measurable precipitation has fallen vs. only 17 weekdays on which measurable precipitation has fallen.  Moreover, because there are more weekdays than weekend days, the percentage of weekend days that have received measurable precipitation is 56%  (32 of 57 days) vs. only 22% for weekdays (17 of 76 days).  I just ran a two-tailed T-Test to determine the probability of this pattern occurring randomly, and it works out to be about one chance in 730. 

So, is this rainy weekend pattern here just a fluke, or is there more to it than that?

[MN Transplant]

I'm on the "just a fluke" side.  The proposed mechanisms for artificial enhancement of precipitation by other means (such as pollution from cars) are likely to be seen only in certain very specific local conditions.  What we are instead seeing is a continuous parade of synoptic-scale systems.  Perhaps the overall Rossby pattern wavelengths are such that there is a repeated pattern on the 6-7 day timescale.

[understudyhero]

Didn't someone write an article about this a year or two ago when it seemed to only snow on weekends?

If we are talking about it multiple years in a row, when does it become statistically significant?

[PrinceFrederickWx]

There was a study done by Arizona State back in 1998 that showed a statistically significant correlation between weekends and rainfall (including tropical systems) on the east coast. At the time, air pollution was blamed- would be interesting to have an updated look, twenty years later: https://www.sciencedaily.com/releases/1998/08/980814070429.htm

[Eskimo Joe]

Likely HAARP and wind turbines...major gov interference!

/chuck

[GramaxRefugee]

20 hours ago, understudyhero said:

Didn't someone write an article about this a year or two ago when it seemed to only snow on weekends?

 

DT did, further back than that. (Sorry, no link but most of us can imagine it, in his entertaining style of writing. )

And that's the thing. These patterns just come along and always have. I'm old. I remember. (Except when I don't. Sorry, I'm old)

[Jebman]

Last year in Dale City at least, there were a few rainy weekends from late May on thru late September. I should know. I was still up there then. It rained and rained, and I had to mow not only my yard but two of my neighbors' yards.

It was The Summer Without The Sun.

[RodneyS]

On 5/13/2019 at 4:07 PM, RodneyS said:

Most of us have complained at some point about rainy days seeming to occur more often on weekends than on weekdays.  However, as the Capital Weather Gang recently noted, that has actually been the case this year in this area, assuming that the weekend is defined to include Friday; see https://www.washingtonpost.com/weather/2019/05/13/washingtons-wettest-days-history-inches-precipitation-have-fallen-past-year/?utm_term=.2bb2b4bf05c4.  Specifically, through the first 19 weeks of 2019 at DCA, there have been 32 weekend days on which measurable precipitation has fallen vs. only 17 weekdays on which measurable precipitation has fallen.  Moreover, because there are more weekdays than weekend days, the percentage of weekend days that have received measurable precipitation is 56%  (32 of 57 days) vs. only 22% for weekdays (17 of 76 days).  I just ran a two-tailed T-Test to determine the probability of this pattern occurring randomly, and it works out to be about one chance in 730. 

So, is this rainy weekend pattern here just a fluke, or is there more to it than that?

It's remarkable how the early rainy DCA weekend pattern reversed during the last 31 weeks of 2019.  During the first 21 weeks, 54% of weekend (Friday-Sunday) days had measurable precipitation vs. only 23% of weekdays. However, during the last 31 weeks,  only 17% of weekend days had measurable precipitation vs. 41% of weekdays.  Overall,  32% of weekend days had measurable precipitation vs. 34% of weekdays.