Blizzard of 2015 post-mortem media blitz

We had a huge snowstorm in the northeast US over the last couple of days. Here in New York City, it was not so huge as was forecast, leading to a lot of discussion in the media (social, traditional, and other) about what went wrong and right.

I have an op-ed in CNN summarizing my take on it. I don’t have a lot to add to that, except to say that if I could write it again there is one sentence I would change: “Being over-prepared, in contrast, merely leads to lots of griping on the Internet.” That’s a little too cavalier; there are real economic costs from all the transit shutdowns. I stand by everything else in the piece, including the overall message that those costs (which are not too huge according to the NY Times today) are a price worth paying for the benefits gained overall from forecasting and proactive emergency management.

I am quoted in stories in the Times, Mashable, and Climate Central saying similar things. Of the many many other interesting pieces on this event, Eric Holthaus’ piece in Slate gives a good inside view into how the Weather Channel arrived at a prediction of low snow numbers for NYC when the Weather Service was still going high, and Dennis Merserau’s piece in Gawker gives some good perspective.

While I think most thoughtful people understand that the proactive stance of the local & state governments was the right one overall, one specific question that seems legitimate is whether the subways really needed to close. They had never closed for snow before, and even in the moment it wasn’t obvious that it was necessary, even assuming the snow totals were going to be as high as forecast. This piece makes it seem as though it was Cuomo’s own – bad – decision, totally imposed by him on the MTA with no input from them, but the front page story in the NY Times today reports that the MTA head recommended it. This is one where I would like to understand the details bit better.

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Slush is life

Last night into this morning we had a little winter storm pass through. The precipitation forecast was tricky. Here in New York City we were, as we often are in winter, very close to the rain-snow line. In the end, we got maybe a couple inches of snow, plus some rain. Walking around today was messy business, with big sloppy puddles and lots of slush. Here’s a photo from my window down onto the street:

slush_jan_24_2015

Many people don’t like this kind of weather. Many people would rather it were a little colder, so that we’d have nothing but clean white snow. (Of course in NYC it is only ever clean and white for a very short while, but never mind.) I get that. But actually, I like the slush.

Before saying anything else I have to admit that I don’t particularly like cold weather, period. I have mediocre circulation in my hands and feet. I get cold. I can enjoy some winter sports, but put me on the nicest ski slope around and then offer me the chance to be instantly transported somewhere warm and I’ll never say no. I grew up here and have lived here most of my life, but apparently I’m still not adjusted to the climate. I still find every winter a little harsh. And I know, a New York City winter is nothing compared to a lot of places.

Maybe that’s why I ended up working on tropical meteorology – thinking warm thoughts is part of my job. (And yes, occasionally I get to go to a conference or a field campaign in a tropical place when it’s winter here.)

So my appreciation for slush is partly about realizing that it could be even colder than it is. But it’s a little more than that. Slush tells us, in the most visceral way possible as it soaks through our shoes, how special a planet we live on. We can have slush only when the temperature is right near the freezing point of water, at which water can coexist in all three of its phases: solid, liquid, vapor.

A planet which has liquid water can support life. As scientists try to figure out if there’s life on Mars, looking for evidence of liquid water there seems to be most of the ballgame. And it’s only in a pretty narrow temperature range – compared to the range of possible planetary climates – that liquid water can exist; too cold and it all freezes (Mars, at least now), too warm and it all evaporates (Venus).

While we may need liquid water to support life, we don’t need ice. But the ice helps us appreciate the liquid. It shows us just how close we are to the edge. When it’s slushy, we can feel the transition between a frozen climate that is fundamentally inhospitable to life (sorry, Canadians, Midwesterners, Russians etc.) and one that isn’t. When I’ve been on a winter car trip to somewhere really cold and snowy, and I’m returning back to somewhere warmer, I always feel something magical at that slushy boundary in between.

On some days, we live right on that boundary. This was one of those days, in a particularly complete and interesting way. Let’s look at some data.

The picture below shows the local sounding — set of upper air measurements taken by weather balloon, plotted vs. height — from our National Weather Service station in Upton, New York (Long Island) from 7 AM local time this morning.

skew_KOKX_012415

This is a “skew-T log-p diagram”. If you don’t know how to read one of these, I’m going to teach you what you need to know for today. It shows all the variables (temperature, humidity, wind) the balloon measured as functions of height, which is on the vertical axis just as you think it would be (see the white numbers just to the right of the vertical axis on the left, which give the height in meters; the blue letters to the left give the pressure, in hectoPascals). The higher you are on the plot, the higher the balloon was.

The two white lines are the temperature and dew point temperature. If they are on top of each other — as they are below about 5000 m (~3 miles up) — that means the atmosphere is saturated, relative humidity = 100%. Not a big surprise, as precipitation was falling when this balloon was flying.

More interesting is the temperature itself. The reason this is called a “skew-T” plot is that the axes are not at right angles — temperature is not on the horizontal axis, but rather on a tilted axis. The blue lines angling up to the right are lines of constant temperature, or isotherms. You can tell the temperature (in Celsius) of each one by the blue number where it hits the bottom. So a vertical line, for example, would mean the balloon is getting colder as it goes up, as it would be crossing blue lines with lower temperatures. In most soundings, from nearly everywhere on earth, the atmosphere does get colder with altitude, with only a few exceptions. (The word “inversion” is used to describe a layer where temperature increases with height; the word itself tells you right away that it’s an exception to a rule.)

Our balloon’s temperature trace, though, tracks right along one of the blue lines in a layer between about 1000 and 2500 m (or between 900 and 750 hPa, if you like). That means that in that layer, temperature was not decreasing with altitude, but staying the same – it was an isothermal layer. And not at any old temperature – the blue line is the one with a zero below it where it hits the bottom of the plot. That means that a roughly mile-thick slab of atmosphere was almost exactly at freezing.

Why would that happen? Most likely the layer started out somewhere in the vicinity of zero C, but with more variation — part of the layer was colder, part warmer. Then precipitation (ice, liquid, or more likely some combination) started falling through it, and freezing and melting. Freezing liquid warms the air by the latent heat of fusion, while melting ice cools it for the same reason. So layers colder than zero would be warmed by freezing rain, while warmer layers would be cooled by melting snow or sleet. This would bring the temperature everywhere towards zero.

Just above the surface, the sounding shows an inversion layer, where temperature increases with height, so any frozen precip had a little more chance to melt before hitting the surface – which was, itself, exactly at zero C, about to become the perfect environment for slush as sunrise warmed it a bit above that temperature.

In other words, not just the ground, but the atmosphere itself was slushy. Organically, perfectly so.

And tonight, the temperature will drop, and we’ll have black ice. I don’t think I’ll be able to write such a happy meditation on that.

Snow and availability in the Holy Land

I’ve been in Israel for the last two weeks, having been invited to give some lectures in the Geophysics department at Tel Aviv University. A major storm moved into the country yesterday, and hasn’t left yet. Here on the coast in Tel Aviv, there have been strong winds and rain. At higher elevations, there is snow, including in Jerusalem (about 800 meters, or 2500 feet, above sea level).

Here is a current map (actually a 12-hour forecast from the GFS model, valid around the present time as I write) showing the surface pressure and precipitation, with Israel in the lower right (northern Israel is right under the strong precipitation maximum):

gfs_pres_12h_eur

And here’s a map showing the upper level flow, 500 hPa geopotential height (contours) and relative vorticity (color shading); note the strong southward dip in the geopotential contours, indicating a strong distortion of the jet:

gfs_500_12h_eur

As it has turned out, the Jerusalem snow hasn’t been as big a deal as some had feared. There has only been a little so far, and it has been followed by rain washing it away. The preparations, on the other hand, had been massive, with roads and schools closed ahead of time and every level of government preparing for the worst.

The preparations for this event, when compared with last winter’s, manifestly show the role of the availability bias, as described by Daniel Kahneman in Thinking Fast and Slow, in human decision-making about risks from rare events.

One side of the availability bias is that we often don’t take risks as seriously as we should if they are risks of things that we have never experienced. This was evident, for example, in the failure of governments in the New York City area to invest in flood-proof infrastructure prior to Sandy, with the poster child being the South Ferry subway station. The new South Ferry station was completed in 2012 and totaled by the storm — despite well-documented evidence, going back at least 20 years, that a hurricane could cause just the kind of flooding that Sandy caused, in that precise spot as well as others. (See my book Storm Surge for details.) Now that Sandy has happened, things have changed and all kinds of investments are being made in more resilient infrastructure. But since until Sandy no such storm had happened in anyone’s lifetime in NYC, it was human nature to act as though it never would happen.

This Israeli storm is showing the flip side of the availability bias. Snow in Israel is relatively rare, but it happened in a big way last year. In December 2013, Jerusalem got a couple of feet of snow. It wasn’t taken seriously enough. People got in cars to drive from other parts of the country to Jerusalem to see the snow in all its novelty, and many got trapped on the road for long periods of time. The city didn’t have enough plows ready, power outages were more widespread than expected, and significant numbers of people had to evacuate to shelters. The country was taken by surprise, with serious consequences.

Not this time. Since a couple of days before the storm, the newspapers here have been full of stories about its approach and about all the government actions to get ready, including more plows, the school and road closings. The US Embassy issued a message to US citizens in Israel warning about the storm.

The forecast was for a big storm, to be sure, but not for one as bad as last winter’s. Having been through last year’s event, though, no way were those in positions of responsibility going to be caught off guard this time. When we have been through a rare and disastrous event recently, the availability bias tends to make us think it’s the “new normal”.

I am not saying that the authorities overreacted to the forecast this time. Their actions may well have been warranted, given some uncertainty in the forecast and the vulnerabilities of the region as demonstrated last winter. But it’s clear that the reaction is erring on the side of caution this time, compared to erring the other way the last.

Still, the storm has been impressive and exciting. I’ve put a short video on my facebook page showing the waves pounding the boardwalk at the Tel Aviv port, in the northern part of the city, last night.

Thanks to Pinhas Alpert for a discussion of the role of availability bias in the preparations for the present storm, to Nili Harnik for inviting and hosting me here, and many people here for accounts of last winter’s storm.