psuhoffman

I will take you at your word that you are not trolling and engage one last time with what I take issue with in your statistical analysis. But first I'll post some data that I will reference in my response below. @Terpeast I have used only DCA data from 1942 onwards. DCA annual snowfall with a linear trendline and 30 year running mean imposed. 18 year running probability of getting at least 10" of snow in any given season 18 yeas was not arbitrary but was chosen because in this discussion yesterday 18 years was agreed upon as a minimum data set to avoid overly skewed results to get a statistically significant result. Some additional facts. The running 30 year mean snowfall at DCA has decreased from 17.8" to 13.9" over the period of record for the airport. This trend is continuing and is getting even worse...the current 15 year mean is only 13.6" The median has decreased from 15.8" to 10.85". This trend is also getting worse. The current 15 year median is 7.8" The chances of getting at least 10" of snow in a given season have gone from 72% to 50% in a given season. This trend also is getting worse...the current 15 year probability is 47% The chances of getting 15" in a season have gone from 53% to 27%. The chances of DC getting 20" have gone from 40% to 17% 1) The words bolded above are all your opinion. The slope is NOT 0, virtually is opinion...yes over any one year the change is insignificant but over a long period of time .03 adds up to 4" of snowfall we have lost annually over the period of record. That is not insignificant when your average is only about 14". That's more than 20% of our annual snowfall we have lost. 2) Single digit snowfall years is not arbitrary, its a way of showing what chance there is of getting a significant amount of snow in any given year in DC. We can use another number if you want...8", 12", 15", 18", 20"...they all show the exact same trend so it doesn't matter. I didn't cherry pick 10 to skew the data, I picked 10 because its a nice simple even number to highlight the issue which is in any given year the odds of getting snow is going down. That is true whether you use the threshold of any amount between about 7 and 20", outside that you get some crazy useless percentages because you're using a number outside a standard deviation. 3)I've repeatedly said that using the probability of snowfall or the median is way more useful to a climate like DC and you repeatedly dismiss that which is your opinion and fine but I will explain what is wrong with a mean. DC snow climo is inflated by anomalously snowy seasons like 1996, 2003, 2010 and 2014. But the snow that happens in those winters doesn't make the years in between any less awful. They do not affect what a typical winter is. Getting a huge amount of snow every 7 years or so affects the mean a lot but isn't indicative of what any given winter is likely to be like...which is probabilistically much more likely to be one of those other 6 years. Median filters out those big years better to give you a better indication of what any given specific season is likely to be like. 4) You've said there is no evidence that the mean is being skewed but the evidence is right on the chart for everyone to see. While the median and probabilities of snowfall are clearly decreasing the range of snowfall in any given year over a period of time is increasing. The standard dev of snowfall is increasing. Even though the baseline for snowfall is lower we have had several of the biggest snowfall seasons recently. This is preventing the mean from dropping as quickly as the probabilities of snow in any given season are. But for our purposes the probabilities are more important. Who cares that it snows a crap ton once every blue moon when the truth is we spend 80% of the time in the total suckage periods in between that are getting worse! 5) You repeatedly try to manipulate the data by using an arbitrary date in the 1980's from which you can say "snowfall has increased since". That is really bad statistically because snowfall does run in cycles. We are no doubt in a down cycle right now. I have never implied DC won't have better snowfall periods ahead. But by cherry picking a date that is a minimum with which to compare the current point in time fails to acknowledge that over a longer period of time its evident that the "snowy" cycles are becoming less snowy and the "dreg" periods are becoming MORE dreg. The current down cycle is no doubt a down cycle...but its worse than previous down cycles. The recent snowy periods weren't as snowy as past snowy periods. Over longer periods the downward trend is evident.

He is trolling... I should have noticed sooner. But no need to continue engaging with childish behavior.

Last time it got this salty in here I got my biggest snow of the last 6 years so I’m liking the vibe.

This X1000000. How anyone can argue with that is beyond me. Yea we can still get an anomalously snowy winter like 2010 and 2014 that skews an “average” but the odds of getting less snow in any given year are going up and I think many have been clear that’s what we’re talking about.

You’re all over the place. 1) Earlier you said “10 years isn’t a big enough sample” and now you’re basing this analysis on 10 years. 2) 1980s avg DC snow 17.1” Median 17.8 with 3 single digit seasons Most recent 10 years avg DV snow 12.3” median 10.5 with 5 single digit seasons. By what metric were you saying the 80s were worse??? 3) If what you mean is you’re comparing 1980s to 2010s then you are still dealing with the 10 year sample size issue, but then my point why I don’t care about the mean cones up. Yes the 1980s (which you cherry picked because they were a previous snow minimum) mean was slightly lower at 17.1 to 17.2. But the 2010s were severely skewed by 2010 and 2014. But the median and single digit snowfalls tell the story. The median snow in the 2010s was only 13.5” compared to 17.8” in the 1980s. There were 4 single digit seasons compared to 3 in the 80s. So even cherry picking the previously worse minimum period and comparing to the 2010s which included 2 extremely anomalous snowy winters…the odds of less snow in any given season were still higher in the 2010s compared to the 1980s which is what I’m talking about. I don’t care about the rare once in 9 years huge seasons that skew and inflate the mean. I’m talking about the fact that in any given season the odds of DC getting less snow (or a single digit season to make the concept simple) is going up and that’s a fact no matter how you try to slice up the data.

Seriously? All you have to do is look at the DC snowfall data. From 1888 to 2000 a single digit snowfall season was fairly rare, then suddenly they are happening more often than not. You want me to waste time throwing that into chart just to prove what you can see from a 10 second look at the data?

The problem has nothing to with the number of years/sample size. The issue is you aren't looking at what I am talking about. I am talking about how DC is getting more single digit snowfall seasons than before and you are looking at a mean which can be skewed by a minority of seasons to hide that phenomenon. We are two ships passing in the night. Neither of us is refuting the other...we are simply focusing on two completely different phenomenons.

Is it partly cloudy or partly sunny?

This is what I suspect. I meant the mean is low and bounded by 0 like Dallen said not that the sample size is low. I think median gives a much better idea of what a "typical" winter was like during any given period of time. For example the last 16 years (this is the period of time where I've really noticed the phenomenon I am hinting at here) there have been 9 single digit snowfall seasons, 4 years between 10-20", 1 season between 20-30" and 2 BIG years above 30" that are skewing the mean. During that time the mean is over 13" but the median is around 8". 8" being much closer to what a typical winter has been in DC over that period since 9 years were single digit snowfall and only 7 were more than that. Thank you, you said what I meant but much better. You're totally right, we need a larger sample size than 10 so I wouldn't use a 10 year median. But you could do a running 20 or 30 year median. But something is going on that is not refutable which is the prevalence of single digit snowfall seasons in DC is skyrocketing lately. Looking at the data there is no 16 year period that even comes close to having 9 single digit seasons. 16 years is starting to become a bit much to continue the "its just recency bias" or "its just a short term blip" mantras. And it's not like its a little off...its way off. I know 16 years is kinda arbitrary but going back over all previous 16 year periods DC had 5, 4, 3, 5, 5, 3, and 3 single digit snowfall seasons....yet during the most recent 16 years there were 9. Even if you try to simply cherry pick the worst 16 year periods you can't get close. The worst you can find cherry picking is another 16 year period with 6 unless you overlap the current period and then you can find 7 single digit seasons, but that is only by including several of the seasons in this current 16 year period. Basically the current most recent 16 years have been the absolute worst in recorded history in DC for getting abysmal low snowfall seasons...and the next worst is a 16 year period overlapping this current 16 year period! And nothing else comes close. That seems significant to me, more significant than to dismiss with "just random chance". The mean doesn't show it as much because a few seasons have been skewing the number enough to hide what I am talking about...which is getting more frequent dreg single digit snowfall seasons . Now what we don't know is this....is this awful stretch just part of a random cyclical thing or a more permanent shift. It's very possible that if records went back further we could find similar awful periods...and perhaps we pull out of this and in the next 16 years only have 3 or 4 single digit seasons (but do you really wanna bet on that???). So I am NOT saying I know this is all due to warming (although I suspect some of it is) but what I am saying is we are in a pretty long term stretch where its more likely than in any other period in recorded history for DC to have single digit snowfall year to year. It's been a long enough period now that until we break out of it...I don't consider it just a blip. Its not been just a few years...this trend has been going on for quite a while now with just a few interruptions by some big seasons here and there. But other than those big seasons....suddenly DC's typical winter is a single digit snowfall...when that used to relatively rare in the past.

A mean of such a low number can be skewed by a few years. I’d be more interested in a statistical analysis of the median and changes in the standard deviation.

I have to admit I was extremely busy and preoccupied much of last winter and what time I did devote to snow was mostly predicated on my ski trips. But…I seem to have a VERY different perception of last winter than many. I’m seeing a lot of posts where people seek to be rooting for a repeat of last year. Here at least last year was one of the worst snowfall winters of the 18 I’ve spent in the area. Finished 18” below avg and 12” below median. I’m definitely NOT rooting for anything that resembles last year. I think this winter will resemble last year, but that’s a negative to me.

What CBM said. The low heights on the mean are from two bowling bowls that progressed through after cutters. As both shortwaves were approaching the critical area there was a WAR and full latitude eastern ridge in front.

You gonna yell at me again if I answer?

Huh….the PNA and SE ridge or WAR are EXACTLY why we wasted one of the most -AO periods ever. You’re right that guidance says that changes, history says it won’t. I’m not taking sides just saying facts.

I agree there is some of fluke in this. But 9/9 (or 13/13 if we include ninos) means something. But I don’t mean it to say there is a 100% chance of below avg snow. If we had more years of records eventually there would be an exception. I don’t think it’s impossible to get a snowy winter when I get no snow through New Years. Just the odds are low enough we haven’t captured an example YET. I also opined that perhaps as November and December warms we’re creating a climo where that is more likely.

Good test of guidance v analogs. Several of this years analogs are in that set and they say don’t get your hopes up. The guidance says we head a different direction than history suggests. Place your bets.

We got a little over an inch on Dec 27th. Picture of my kids playing in it. It was barely snow, temp 33-34, rain all around us at lower elevations. only the ridgetops really got it.

Adding El Niño’s doesn’t make they much difference up here like it does for DC. The 4 El Niño’s that started with no snow were all below avg. 2 were awful, 72-73 and 91-92. The other 2 recovered to be respectable but still well below avg snow. Overall in 97 years or records here there are only 13 years that got to January without 1” of snow. They all ended up way below avg snow and 12 of the 13 are on the list of 15 least snowy years here! So basically every single time we didn’t get snow up here by January it was a horrible snow season here. But there is a first time for anything. And for some places in the southern parts of this forum it’s not as dire where one fluke 8” snow can make the season ok.

Off the top of my head I think the non Nino years with less than 1” were 1949-50, 54-55, 58-59, 75-76, 80-81, 84-85, 2001-02, 16-17, 19-20

You know I’m just messing with ya. We all know you know what you’re talking about. Yes the pattern looks good after the first week of January. All my posts are simply pure statistics and climo based because historically Ninas that start bad don’t end well. Given the last total pattern fail I just don’t have the stomach to dive back into day 15 diagnostics. Get a legit threat inside day 5 and I’ll get excited though. Yes but it’s not always a FAIL month. What’s more typical, or was, is we get a lot of frustrating mostly misses but the DC area does get some minor snowfalls. Some 1-2” type stuff. We just don’t remember them because they were seen as fails when just NW of there (like me) got 8”. And up here getting to January with no snow is pretty rare. So yea Dec is usually a small f fail but not always a total FAIL like this. The point of my data was to show that yes we do get a lot of total fails but unfortunately we also get a lot of really bad snowfall years and they tend to be the same often. It's sad. Temps thus month are solidly below average. Precip is above average and yet...no snow So ending on a positive note, was thinking maybe since we’re losing snow climo on the edges most, and early season would logically be impacted most with the warmer SST feeding the SE ridge, in that new climo perhaps it will become more common to have a total dud Dec and still flip snowy in January. If true can’t get back what we lost in a Dec so maybe a 28” winter becomes a 24” one or something like that. But maybe this year will be the first time we went into January with no snow then ended up with a big snowfall year. It’s possible.

It could help. Or it could send the PV to the other side of the world. No way to know.

@Maestrobjwa but if you need to be talked off a ledge the sample size is too small to say there can’t be a fluke. There is probably like a 10% chance we get a result better then any of the previous cohort.

If snow affects you emotionally this much, to the point of affecting your enjoyment of Christmas, you really need to move somewhere that snow isn’t an anomaly! You also need to examine if this hobby is healthy for you. If this upset you like this why did you ask me to share the imfo and why are you here now when you know we’re staring at a no hope shit the blinds pattern setting in. There was not going to be anything good here yet you made the choice to read. I love snow but for me it’s also about the science and weather in general. But I also have other vices and joys I can simply transition to when snow isn’t gonna happen. How do you even survive April to October of snow is this central to your emotional state???