WesternFringe

So, the more chances we have the lower our chance of getting snow? Got it! Lol Agree the middle of the month looks the most promising at this point, but I am not sleeping on the first two. At least we finally have some tracking to do.

Will do eta: We all don’t live in the exact same place, latitude, or elevation in this forum, so what the models show varies accordingly. God forbid I say anything positive in this MidAtlantic forum concerning short-term or long-term snow prospects. Sheesh. This is a special place! Lol

Agreed, but if the GFS can bust by hundreds of miles with any given precip from 5 days out, then it can be off with surface temps by 2 degrees. Of course, that works both ways.

And I was just joking about about how analogs, which are computer models, suck at telling us what our February snow will look like. Therefore, I agree with you to not punt February

Yes, the models that fail at predicting snowfall at 7-10 days away 90%+ of the time make it knowable and 100% certain we will get no snow in February.

And it is under 15 days? Lock it in! ETA: fingers crossed!

Here is precipitation for DC by month and by season and by year since the 1870s. I don’t have time to run the numbers right now (especially if you already have), but a quick look tells me there is no obvious increasing trend for winter precip in DC. If anything, it looks to me like there used to be more in the late 1800s and throughout much of the 1900s when compared to the last 30 years. I will run the numbers later, but again, if you’ve done this analysis already, by all means share it with us. https://www.weather.gov/media/lwx/climate/dcaprecip.pdf eta: in fact, I would be willing to bet good money that DC winter precip and snowfall are highly and positively correlated, rather than negatively correlated as you suggest.

So, 50% of years DC gets 8” to 24”, 25% of years are more and 25% less. I hear you that box and whisker plots have limited usefulness, but it is still informative to look at the data in as many ways as possible.

It sounds like you have already done this analysis since you have come to a conclusion, so why would you ask me to ‘do us a favor’ and do it? Either you have done it already and it would be wasting my time, or you are talking smack like you know the results without having done the analysis. Which is it?

If it were warming quickly or significantly enough to affect the snowfall totals (dependent variable) over time (independent variable), then it would show up as a part of the R squared

There is a psychological phenomenon known as the primacy and recency effect. People tend to remember the beginning and end of a list of numbers better than the numbers in the middle. Same with words. It also applies to memories. People tend to remember their childhoods and early memories better than what comes in between. They tend to remember the last few years better than what is in the middle, too. A bunch of people in here seem to remember childhood years full of snow and then remember/note the last 5 or so have sucked for their location. I think this creates misinterpretations and develops biases. For me, looking at means over long periods of time helps to balance out and distinguish my perception from reality.

@psuhoffman I am not meaning to imply that the change has only been .06” since 1942. I know what the slope means, and I think most folks, including PSU, know what I meant. I do think it is difficult for most people (even snow weenies like us) to notice a 1.5” change in annual snow over a 30 year period. I barely notice a 1.5” change between 2 consecutive years. PSU, you make valid points, and everything you say is true as well. Indeed, we are looking at very different metrics of the same data. I don’t care what the snowfall is in 100 years from now either. I do care about looking at the data and yes the cycles and using it to form what my best guess is for the next 40 years. DC is definitely in a bad cycle overall in the latest couple of years. Like I said, I had 28.5” last year, which is about 4 inches above my mean. Therefore, I have a different perspective than a lot of the DC centered folks in here. Our strongest area of agreement is when you conceded that it all might be cyclical. Looking at the R squared, I think it is and that the data show it. I don’t agree that we can discount the R squared because we know there is a (small) warming trend. The R squared should respond accordingly if this were playing a huge role in drastically cutting our snowfall totals. Admittedly, some of the other time periods I ran a regression for had the R squared at more like 94%, meaning 6% was not due to random noise. That’s actually a decent signal that something other than natural variability is at play and that warming plays a part. Our approaches to the numbers and our desires for future snowfall are different. You seem to be more focused on the chances for any given year of getting x amount of snow. I am definitely more focused on how many inches total we get in the next 10, 20, and up to 40 years (if I live that long!). I could care less if it happens in big bunches or whether it is spread evenly amongst the years. In fact, I would probably vote for larger events and bigger years mixed in with dismal years than getting 15” every year like clockwork. Different strokes for different folks. ETA: Trust me though, I will be watching the R squared like a hawk. If DC continues to have 5 year runs with relatively little snow without bonanza years mixed in, the R squared will rise quickly and I will be worried. Or throw in the towel or move north to New England or Upstate NY where I grew up! Lol Imo, I just don’t think the data warrant any panicking yet. I think it is primarily cycles and noise at this point in time.

@psuhoffman When we grade students (you are in education like me, right?), do we use the median or the mean? Why? Do we use GPA (Grade Point Average) or GMA (Grade Median Average)? Why? We use the mean because it better represents all of a student's scores, not just the one grade in the middle. Now, I am fully aware that outliers can skew the mean, but with an n of 136, that isn't an issue. We worry about outliers skewing the mean when we have a low n (< 18), not with an n over 100. This is why educators are usually required to have a certain minimum threshold for number of grades in determining a student's final grade. I know no statistician that would be worried about skewing the mean with an n of 136, especially when none of the numbers in the data set are more than 4 times the mean. If we had outliers of 200" of snow in a year when the mean is 15", then maybe. Don't we wish. But these annual snowfall outliers count, and should be represented in the data. By using the median, one essentially takes all of the best years out of the data and reduces the n precipitously. This is a bad idea, especially with snow! lol I am not saying that snowfall isn't decreasing for DC, but I am saying it has not been a drastic decrease (especially in our lifetimes). This is the data set I used: https://www.weather.gov/media/lwx/climate/dcasnow.pdf I ran another linear regression starting with 1942, as you did. The slope of that line is -0.058" and the standard error is -0.054". The R squared is .01, which means 99% of the variability from year to year is random and not do to the independent variable, which in this case is time (presumably the climate changing over time). So, yes, DC is seeing .058" inches less of snow per year since 1942. Most people wouldn't be able to notice the difference of .058" of snow per year. If you can, you have superhuman perception. 99% (R squared) of the change in annual snowfall from 1942 is explained by randomness, and not due to the passage of time. The slope of the line goes down and up depending on the starting point, of course. When I choose different starting points closer to present (to match the ages of folks in here and thus their winter memories), the slope of the line can be literally almost 0, or can actually be positive. In summary, I concede that the slope of the line is negative, and always have in my posts. However, I also have learned that the human brain constantly looks for patterns and trends, even when they are non-existent or super small. That is why I like stats and means and cold hard numbers. Hats off to you sir if you can notice a decline of hundredths of an inch per year where 99% of the change is due to randomness, or statistical noise. No one can tell the future, but if I had to guess we have some monster years coming up in the El Nino years which will make the slope flatter and closer to zero. The sky isn't falling, we can still do snow, and good years lie ahead. When 99% of the variability is random statistical noise, this tells me we are not in some inevitable downward spiral regarding snowfall. Again, I stick by my conclusion that although annual DC snowfall is falling (no pun intended), the change is very small, not cataclysmic, and 99% due to randomness.

Honestly, this has me nerded out and I want to respond with specifics rn, but I need to take my daughter to her grandma’s house and eat dinner. I will get back to you tonight or tomorrow! ETA: Did Mappy guide you to guide me here? Lol

Also this. eta: I had to take a break from this thread bc of all the vitriol and ad hominem attacks (always a good way to win an argument (eye roll)) like calling me childish. I had to laugh eventually. Imagine the vitriol if I had said we will never snow here like we have snowed before! Or if I said the data show we will never be snowy again! I wonder whether some folks here would have just nodded along and said you are right. i got attacked for saying the data don’t show a huge downturn and implying that we might get normal to above snowfall soon. And that it is location dependent and not an observable trend statistically. Lol i looked at the data set of annual snowfall with clear eyes. I took Stats 1,2,3, and 4 at UVa when studying for my doctorate. But suddenly I am trolling and childish when I say the data for DC statistically don’t show a cataclysmic drop in annual snowfall? Someone needs a reality and self over confidence/assurance check, but I don’t think it is me, since my self confidence was in the gutter following the hostile attacks last night. I stand by my data analysis, and don’t think the sky is falling and it is not is it ‘harder to snow around here’ anymore. We are just in a bad stretch for some in some parts of the mid atlantic.

This.

Well, folks are wrong then. I ran the numbers and the slope of the line is virtually zero. Yes, DC is getting .03” less per year on average over the 140 year period. That is statistical noise. DC is getting 0.17” more per year since 1960s. That is also statistical noise. The single digit snowfall years ‘trend’ is arbitrary, too. Some years with 2 recordable events might yield 9.8” for the season and some years a 10.2” total could have come from 6 recordable storms. We would need to look at snowfall per event by year to make any valid conclusions on snowstorms trending bigger or not. i am not trolling. I simply am saying the numbers in DC at least do not point to a cataclysmic drop in snowfall over the last century and a half. They just don’t.

140 years of data says otherwise. But emotion away

No, it is about how the median better represents 140 year data sets and how 10” is a magic cutoff for judging yearly snowfall in DC, as are certain decades better comparison decades than others. When in reality, annual snowfall remains much the same across 140 years. And yes, across cities as well. So, mock away. But facts are facts. And average annual snowfall is relatively unchanged in DCA in 140 years. And is relatively unchanged statistically in most east coast cities now that I am looking into it. And how many want to explain our poor run of snowfall luck and the unchanging average on more bigger storms and less smaller storms as a result of global warming. Even though global warming predicts the opposite (less big storms).

Okay, now do the 40s compared to the 2000s we can do this all day

Cherry picking. IPCC predicts less big storms as we warm, not more. Kinda destroys the whole “more big storms is the reason for the unchanging mean” narrative.

Talk about cherry picking, lol. Across many cities, we recently had our 4th best of the last 11 decades for snowfall, if we want to look by decade (which I don’t think is very smart).

I guess. I think perspective is king and the proper perspective is the whole data set, not our limited lifetimes.

I have been here, with no one showing me statistical analysis of DCA getting less snowfall on average other than noise since 1888. I can show you the equation of the line of best fit. Where have you been? ETA: teach me all you know about linear regression, SnowenOutThere. I will wait while you Google.

Since 1984, DCA has averaged 0.17” more snow more per year annually. I didn’t go by decades. Nor did I change my analysis based on that. That is a lie. I went by year markers until present with all of my analysis.