WesternFringe

4 minutes ago, Steve25 said:

My point was that it keeps being repeated yet this thread continues to hype up this potential. It just doesn't make sense. We have a hard enough time getting substantial snows in general, then you add in that we're in a La Nina, and that this potential has no true cold air to tap into and the fact that there's any buzz in here just makes little sense. 

If you are certain of what is going to happen, then why are you here?

eta:  I think even though we all know the air mass isn't ideal, the CMC, GFS, and Euro have all shown us glimpses of how we can still get it done.  That's why the thread gets hyped.

3 minutes ago, Weather Will said:

WB 12Z EURO v GFS….over. Wait for EPS.

Why are we looking at 850s for what would be Jan 11th 7:00pm EST here when our storm would be on the 15th?

27 minutes ago, CAPE said:

Just ignore the surface temps.

Rates will overcome!

1 minute ago, umdterps29 said:

Can someone post the Kuchera just for giggles? Would love to see what it looks like for Deep Creek. They need it bad.

24 minutes ago, nj2va said:

Wooooh boy, love that run for the mountains.

Yeah, I will take my 14" and run with it!  

I am starting to believe in atmospheric memory!    For Augusta County it looks like a mix of rain, snow, and sleet just like 12/15 and 12/22.  

11 minutes ago, WxUSAF said:

I’d wag ratios would be like 5-6:1 in places that are cold enough to accumulate. White rain in warmer spots.

NAMs thoughts.  Better than I thought they would be

I posted the 0Z- thx Solution Man

Here is snow depth on the NAM

NAM'd!

3 minutes ago, MDScienceTeacher said:

For years, all I would care about would be the big time snow events.  If the long range model wasnt putting out 12+ inches, then I didnt care.  Over the years however, I have learned that this is a losing proposition and promotes misery in my life.  I think I finally have gotten to the point where I would be happy with just some snow.  Or maybe more frequent smaller storms. 

Getting wrapped up in the KUs and BECS and HECS and Bombs etc is a tough business to be in..

 

I have been on here for years, and I know that KU storms are the biggest of all the storms.  However, I still have no idea what the abbreviation stands for.  Can someone enlighten me?

1 hour ago, Kevin Reilly said:

So, a 33% Chance.  So, you are telling me we have a chance!!

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.

40 minutes ago, mappy said:

do with the information what you feel like doing with it. just saying as shown today those snow maps are probably wrong.

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

2 minutes ago, mappy said:

of course! just didn't want people to think they'd be seeing 2 inches of snow with temps at 33

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.

5 hours ago, Ralph Wiggum said:

Not what I said at all. Nothing about models. Ppl are using Nina analogs to assume February will be punted. I think it's a narrow way to think which is why I wanted to hear from others on this board.

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 

2 hours ago, Ralph Wiggum said:

Seeing lots of chatter recently about how Feb is going to be trash with a raging SER and -PNA. What makes this thinking such a lock? Is it really a 99.9% certainty that Feb will be punted? 

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. 

2 hours ago, Ralph Wiggum said:

Now THATS a signal. Deep eastern slight neg tilt trof on the means. 

And it is under 15 days? Lock it in!

ETA: fingers crossed!

13 hours ago, fujiwara79 said:

The 30-year snowfall average at DCA has decreased by 20% since 1941.  But there has also been a significant increase in the 30-year wintertime precipitation average.  A decrease in wintertime snow, juxtaposed with an increase in wintertime precipitation, is strong evidence that there probably are more "33 and rain" events lately - and that it's not just our imagination.

Do us a favor and check what percentage of each winter's (for simplicity, use DJF) precipitation falls as frozen, and show us how that has varied over time.  You'll find that the percentage of precipitation that falls as frozen has markedly decreased.  Bigly.   

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.

30 minutes ago, 87storms said:

I think the median is important for the sake of trying to find out what the 50th percentile is.  If you like snow and don't need the big dog storms, then you'd obviously want a higher median.  Just running a box and whisker plot on the DCA data since 1887 (I know, it's not ideal) shows the IQR to be from 8" to 24".

 

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.

10 hours ago, fujiwara79 said:

The 30-year snowfall average at DCA has decreased by 20% since 1941.  But there has also been a significant increase in the 30-year wintertime precipitation average.  A decrease in wintertime snow, juxtaposed with an increase in wintertime precipitation, is strong evidence that there probably are more "33 and rain" events lately - and that it's not just our imagination.

Do us a favor and check what percentage of each winter's (for simplicity, use DJF) precipitation falls as frozen, and show us how that has varied over time.  You'll find that the percentage of precipitation that falls as frozen has markedly decreased.  Bigly.   

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?

2 hours ago, pazzo83 said:

isn't your independent variable here time, so that is what you are using to try to explain the variance in your observed data (snowfall)?  Let's ignore the fact that running a simple linear regression on a time series, especially when there is a cyclical component here (thus the observations are not all IID), is problematic.  But if you are trying to see if a warming base state would be used, you'd think you'd include something reflecting that in your analysis (and not just time).

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.

1 hour ago, WinterFire said:

This part. I’m not sure if you’re meaning to imply this, @WesternFringe, but focusing on an annual average change of -.06” makes it seem like your argument is that DC winters have only seen a decrease of .06” from 1941 to today. But that’s not what a slope of -.06 implies—rather, it’s indicating that the annual snowfall from 1941 has decreased by a total of something like 4.5”. Which is noticeable, I’d argue. So yes, between last year and this year, most people would not notice a decrease of .06”. But over the last 30 years, we do notice a decrease of nearly 2” (which incidentally matches relatively closely with the 30 year average in the 00s of 15.4”/year compared to the 20s average of 13.9”/year). 

@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.

15 hours ago, psuhoffman said:

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.  

 

@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