
Boston’s astounding month of snow a 1-in-26,315 year occurrence - cryptoz
http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2015/02/25/bostons-astounding-month-of-snow-a-1-in-26315-year-occurrence/
======
PhantomPhreak
Only 21,000 years ago, Boston was buried under a sheet of ice over a kilometer
thick.

Source: [http://xkcd.com/1225/](http://xkcd.com/1225/)

~~~
cottonseed
I've been wondering how much snow needs to drop before we start growing
glaciers.

~~~
dredmorbius
It's less a matter of snow _fall_ and more one of snow _accumulation_.

For snow to _fall_ you want _warmer_ temperatures (relatively) which allow
_large amounts of atmospheric moisture_. Ideally striking a cold air mass
which then causes snow to fall. Most notably in the U.S. in the form of "lake
effect snow", where warmer, moister air over the Great Lakes moves (typically
NW to SE) over colder land, and dumps often major amounts of precipitation:

[http://eoimages.gsfc.nasa.gov/images/imagerecords/17000/1777...](http://eoimages.gsfc.nasa.gov/images/imagerecords/17000/17770/GreatLakes_TMO_2006343_lrg.jpg)

For snow to _accumulate_ you need _annual temperatures which remain below
freezing_. In this case, _even with modest amounts of annual precipitation you
can achieve large ice sheets_. The annual _precipitation_ over the Antarctic
is quite low: "As strange as it sounds, however, Antarctica is essentially a
desert. The average yearly total precipitation is about two inches."

[http://www.antarcticconnection.com/shopcontent.asp?type=weat...](http://www.antarcticconnection.com/shopcontent.asp?type=weather-
snow-ice)

But with an annual average temperature _well_ below freezing, _any snow which
falls will accumulate_.

The daily _high_ temperature in Boston is above freezing _every month of the
year_ , and the low from mid March to early December. Odds of Boston being
covered in kilometer-thick ice sheets any time in the near future are
exceedingly low.

[https://weatherspark.com/averages/29794/Boston-
Massachusetts...](https://weatherspark.com/averages/29794/Boston-
Massachusetts-United-States)

------
atourgates
It's been an interesting winter. We've had more or less the opposite here in
the Pacific Northwest.

Many of the Cascade ski resorts are either fully or partially closed. Further
inland things haven't been much better in terms of snowfall[1]. We moved into
a house in Idaho this summer with a long driveway that typically has 1'-3' of
snow for a month or two every winter, but I took the plow off our UTV 3 weeks
ago, after only having used it once (on about 4" of snow) the entire winter.

While of course climate isn't equal to weather one interesting side effect is
that I've heard quite a few people say things along the lines of "Ok, I
believe in global warming now." I'd imagine the reaction has been quite
different in Boston.

[1]
[http://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/...](http://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/1stmonth/westwide/swe/WestwideSWEPercent_Feb.pdf)

~~~
squidfood
The warm PNW and the cold NE are intimately related:

[http://cliffmass.blogspot.com/2015/02/why-is-northwest-
warm-...](http://cliffmass.blogspot.com/2015/02/why-is-northwest-warm-and-
california.html): "It is quite easy to explain the proximate cause of the
warmth over the Northwest, the drought over California, and the cold/snow over
the eastern U.S. They are all caused by the same basic phenomenon: a high
amplitude upper level pattern with a persistent ridge over the West Coast and
a trough over the eastern U.S."

~~~
btilly
That article is accurate, but does not pull the pieces together. Let me fix
that.

We all know that hot air rises, and cold air sinks. Therefore if you heat one
place and cool another, air will rise in the one, move to the other, and then
sink. The Earth is heated up near the equator, and cooled near the poles, so
we show that pattern. It actually repeats several times, and the result are
the Hadley cells. See
[http://en.wikipedia.org/wiki/Hadley_cell](http://en.wikipedia.org/wiki/Hadley_cell)
for confirmation of this.

However in the Earth there is a complication. We are rotating. When air rises,
then moves towards the pole, it maintains its angular momentum, and now goes a
_lot_ faster than the ground. Thus the air that is about to come back down is
going very fast. We call this the jet stream. (There are actually a few jet
streams at different latitudes.) When it comes down, the ground slows it down,
but it results in a prevailing wind. Over the oceans those winds are called
the trade winds because sailing ships used to follow routes that used them.
The one over the US goes from west to east, and that is why many major storms
tend to do that.

Next piece of information. The nice symmetrical structure I've drawn so far is
unstable. It is prone to develop kinks and bends, which then grow. Around the
world the overall average latitude is reasonably well fixed, just not the
exact latitude at a specific spot. The result is that the jet stream tends to
develop fairly large standing waves which are fairly long-lasting but do move
around.

Now go get a globe and look on it. North America turns out to be roughly half
a wavelength for one of these standing waves. So if the jet stream goes north
on the Pacific side, it will go south by the Atlantic. This is our current
pattern and it results in a mild winter on one side of the country and a
severe one on the other. If the wave is flipped in another year, the pattern
reverses. Or you can have a phase shift and both coasts can be average and the
interior can be either warm or cold.

This has been known for decades and has nothing directly to do with global
warming. (I learned it all from a fluid mechanics course that I took in 1992.)

~~~
hyperbovine
"Directly" is practically meaningless when discussing cause and effect in a
system as complex as the global climate. But there is ample evidence that
arctic warming, for example, can profoundly alter circulation patterns in the
upper atmosphere, which lead to extreme weather events in more temperate
regions ([http://skepticalscience.com/jetstream-
guide.html](http://skepticalscience.com/jetstream-guide.html)). Personally,
it's a lot easier for me to buy that the climate has altered than that I'm
witnessing a true once-in-25000-years weather event.

~~~
btilly
The jet stream, being chaotic, can be affected by _anything_.

That said, the locations of the Hadley cells changes depending on how much
heat is stored in the system, and adjustments to this is part of the whole El
Niño, La Niña cycle. As you increase the rate of energy storage, this results
in various chaotic changes, that can increase extreme events.

But the real problem with the rarity of the event is that you arrive at that
figure by a probability model assuming independent storms, probably with a
Poisson model for frequency. However storms are not actually independent
events. If you have a stable pattern that results in many storms following the
same track to Boston, the odds of an extreme event are way higher than the
naive probability model would have suggested.

~~~
hyperbovine
Agreed, but the more problematic assumption is that the Poisson rate function
is time homogeneous is what I'm saying.

------
bceagle
I have to say this past month living in Boston has been really challenging on
so many levels. Tension from difficulties getting to work, playing chicken on
the narrow roadways, inability to get out of the house with the kids, finding
baby sitters to cover when school is cancelled and the never ending shoveling.
I love Boston, but I would not be able to take many more winters like this
one.

If I had to narrow things down to one primary issue, though, I would have to
say it is the total failure of the public transit system, the MBTA. Things
wouldn't be nearly as bad if the T was running smoothly, but even now the
commuter rail is running on a reduced schedule (which results in completely
packed trains that are often late) and various subways trains break down on a
daily basis.

Not fun.

~~~
otakucode
Given the rarity of such an event, wouldn't the wisest course of action be to
simply shut everything down for awhile? The nation of Sweden pretty much shuts
down for a month every single year, I don't see why Boston couldn't handle
doing it once every few thousands years.

------
rcarrigan87
I may be looking a little too much into this headline, but I really think it
speaks to the way humans look at the earth as some static, immutable system.

How could someone even go about calculating these odds on something so
dynamic. Boston was literally under ice 20K years ago and will probably be
completely under water in another 20K years.

~~~
burkaman
The article covers it pretty well. This is just a simulation done for fun
based on current climate conditions. Right after that they acknowledge that
"Of course the climate isn't static" and offer a possible explanation for the
huge increase in snow.

But I think the point of the article is that even taking into account recent
climate changes, this is still a super unlikely string of storms, and there's
a lot of chance and coincidence involved.

------
thirdtruck
As someone raised in the south, I picked a heck of a year to move up to
Massachusetts, didn't I?

What do you all do to avoid going stir-crazy when the snow leaves you stuck
inside the house for days?

~~~
pyrois
Fight over parking spaces. It's Boston's favorite winter pastime.

~~~
dogecoinbase
Just go around removing space-savers, then let Boston tear itself apart.

~~~
vacri
Never having lived in the snow, this concept was new to me. It lead me to this
terrible article[1] which says the same thing in each of it's four
paragraphs(!), but linked to this article[2] which has a better description of
the cultural phenomenon, including some light flamewarring in the comments...

[1][http://www.wbur.org/2015/02/23/space-saver-
enforcement](http://www.wbur.org/2015/02/23/space-saver-enforcement)
[2][http://www.wbur.org/2015/01/28/space-savers-
boston](http://www.wbur.org/2015/01/28/space-savers-boston)

------
Retric
IMO, 1 in 26,315 years is a terrible way to present low odd events. 4 per
100,000 years is much better as people don't think this can't happen again in
my lifetime and you don't add a lot of false accuracy.

PS: Also, these are not independent events so those long tail odds are likely
way off base.

~~~
ryandvm
Who thinks they're going to live 26,000 years?

~~~
maxerickson
That's exactly the intended meaning.

Using 1 as the first number in the ratio makes people think of it like a
comet, once you see it you won't see it again for the given period (and will
not live to see another).

Using 4 in 100,000 would be an attempt to get more people to reason clearly
about what the odds mean.

------
grecy
I live in the Yukon, and more than once this "winter" Yukon has been the
hottest place in Canada, so we're all talking more and more about climate
change and how nothing is what it used to be.

In the years to come, I'm expecting headlines like this (ridiculous odds about
odd weather) to become perfectly normal.

~~~
tjradcliffe
Under-prediction of warming in the north is one of the most notable failures
of climate models, although they are wrong on lots of other details as well.
This is not a surprise: climate models are in important respects non-physical
approximations to the real climate, and as such can't be expected to get the
details right.

Depending on your politics you can now accuse me either of making excuses for
"the hiatus", or of being a Denialist, but all I'm really doing is pointing
out that the public's expectations of climate models is both too high ("the
science is settled") and too low ("global warming is a hoax!")

There is a middle way between these extremes, one that acknowledges the
uncertainty of the models (which are large) while at the same time recognizing
that there is no physically reasonable way to double the CO2 content of the
Earth's atmosphere without adding about 1 W/m __2 to the heat budget.

That we don't have a very good idea of how the Earth's climate will respond to
that additional heating is not something we should find reassuring, and while
there are plenty of good reasons for investing in nuclear, solar and other
alternative power sources, there are also good reasons to invest in climate
robustness: ensuring that our cities aren't entirely shut down by a rare
snowfall, investing to protect the most vulnerable populations from climate
variation from any source, and so on.

Our economies are highly tuned up for the climate of the past 100 years, which
was unusually stable. We should be aware that the kind of forward planning our
parent's and grandparent's generations did based on the assumption of climate
stability is not likely to be viable in future as the climate returns to its
state of natural volatility, almost certainly helped along by anthropogenic
contributions.

~~~
grecy
> _Our economies are highly tuned up for the climate of the past 100 years,
> which was unusually stable. We should be aware that the kind of forward
> planning our parent 's and grandparent's generations did based on the
> assumption of climate stability is not likely to be viable in future as the
> climate returns to its state of natural volatility, almost certainly helped
> along by anthropogenic contributions._

Nicely put.

To be honest, when I'm having these conversations I don't go near the whole
debate of global warming / we did it / co2 / etc.

I think its simply important to acknowledge the climate _is_ changing, and we
need to get with the program. _Why_ it's changing is a whole other thing for
another day.

------
smackfu
The amount of snow is only half the story. It's also been very cold, way below
freezing, so the snow is just not melting. If you get a foot on Wednesday and
a foot on Friday, but it melts in between, that is much easier to deal with.

------
SagelyGuru
"Boston’s astounding month of snow a 1-in-26,315 year occurrence"

Until next year!

------
MengerSponge
That's oddly specific. Why cut it off at the year? It looks like their model
is accurate enough to tack on months and maybe even days to that number!

------
forgotAgain
I think they should have led with Boston having gotten more snow than Buffalo
has ever recorded in a similar time period. Now that's remarkable!

