December 2015’s crazy weather

I’m in Oregon, where December has broken rainfall records east of the Cascades, and the Cascades themselves are deep in snow. I got to see some of it up by Mt. Hood yesterday on a Christmas Day family cross-country ski outing.

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Though that was beautiful, I’m still sad to be missing the record-breaking warmth back east. (I like warm weather; it’s not an accident that most of my research over my career to date has been about tropical meteorology.) To help myself experience it vicariously, I wrote an op-ed piece for CNN about what the probable causes are. It has even been translated into Spanish.

Sudden excitement in the forecast

Update: Tropical Depression Eleven has already been upgraded and is now Tropical Storm Joaquin.

Some weather models shifted their predictions today from what they had been just before. Now New York City, along with much of the rest of the northeast US, is in the headlights of a weather event with some potential. We are now in the forecast cone of uncertainty of a tropical cyclone: currently it’s Tropical Depression Eleven, could intensify to become Tropical Storm Joaquin. Here is the track forecast map from the National Hurricane Center:

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There is still quite a lot of uncertainty with this system, with the GFS model predicting it to be less likely than the ECMWF does that we’ll be hit by this storm. There are faint echoes of Sandy in that model disagreement – the EC predicted landfall earlier than GFS did then too. It doesn’t look like Eleven/Joaquin stands much chance of becoming an event of that magnitude, though, at least not as a wind or surge event (though never say never, or at least not yet).

There does seem to be good potential for heavy rain. Maybe very heavy, as tropical moisture funnels up from the south into a cold front that will be hanging around our region for a few days. NOAA’s precipitation forecast for the next five days puts over five inches of rain on a very large stretch of real estate from the Mid-Atlantic up to northern Maine:

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Some model runs are producing numbers as high as double that – around ten inches – for NYC. This is perhaps unlikely, but possible.

The media is starting to pick up on this. Jason Samenow of the Capital Weather Gang has a nice summary; Weather.com has picked it up; and here is a local NYC TV take on it. From a quick scan, this coverage looks reasonable. It’s giving a sense of what the more extreme outcomes could be, while clearly stating that the uncertainties are still significant. This is as it should be. This is in the “stay tuned” category.

On Sandy’s return period

I’m making it a bit of a mission to recruit younger colleagues, especially postdocs and graduate students, to try writing for nonscientist audiences. In this piece, new PhD Madeleine Lopeman (Columbia Civil Engineering, just defended her thesis, advisor Prof. George Deodatis), explains how her innovative extreme value analysis of tide gauge data at the Battery yields a lower return period for Sandy than all previous ones – meaning maybe it wasn’t all that rare an event after all.

An interesting question is what relationship there is, if any, between return periods defined for different characteristics, either of the storm itself or its impacts. Tim Hall and I published a paper in 2013, for example, that estimated a 700-year return period (95% confidence interval 400-1400 years) for the track of Sandy – strictly, for a storm with at least category 1 intensity intersecting the New Jersey coast at an angle at least as steep as Sandy’s track did. Despite the different numbers, our estimate could be consistent with Madeleine’s, because the numbers describe two different things. It’s reasonable to expect the return period for the flood at the Battery to be shorter than that for the track, because one could get the same flood from tracks coming in at shallower angles if the storm had stronger winds, or made landfall closer to NYC.

Climate change as a storytelling problem

About 2 months ago I had the opportunity to speak in the TEDx Broadway 2015 conference. I spoke about the psychological difficulty of taking climate change as seriously as we should, because it seems like a long-term problem. Since I was speaking to people in the theatre industry, I related that to the problem of making good fictional stories about climate change. I proposed my own idea for a climate change scifi movie, you have to watch to find out what it is (I’m talking to you, Marvel Comics).

Spring ahead

As I write the temperature in NYC is approaching 80F. Most trees, though, are still leafless.

It’s not unusual to have days like this here around this time of year, when the temperature races ahead of the foliage as the sun rapidly climbs higher in the sky. This year the leaves and flowers are coming in late, making a day like today almost inevitable.

I haven’t been able to find a quantitative analysis online of just how late this year’s leafout is, relative to long-term averages, but the cherry blossoms in Washington, DC seem to have peaked about a week late, and my guess is that we’re running at least that far behind schedule here in New York after the harsh winter we had.

The long-term trend, on the other hand, is towards earlier blooming as the climate warms. But as with everything else about late winter and early spring, you wouldn’t have known that from this year in the northeast.

I went for a walk this afternoon along the Hudson River promenade, and it was a good few degrees cooler down by the water. The transition seasons are when the temperature contrast between land and large bodies of water peaks, as the large thermal inertia of the water remembers the season past while the land responds quickly to the sun.

Back in March, when it seemed like winter would never end, I found it comforting to keep reminding myself that the seasonal cycle is inexorable – nothing stops the earth’s orbit.

Sometimes in climate change debates, you hear someone ask “If meteorologists can’t predict the weather two weeks in advance, how can they predict it 50 or 100 years in advance?” The basic answer is that we aren’t predicting weather far in the future, only climate. The two are different. The seasonal cycle provides a useful way to make this less abstract.

I can’t predict exactly what the weather will be on July 4th, but I can predict with unshakeable confidence that it will be a lot warmer than it was in February or March. In fact, I can predict that summer will be warmer than winter every year, forever. That is a climate forecast. The seasons change because of changes in the radiation incoming at the top of the atmosphere, and that’s exactly the same reason that greenhouse gases are inducing a long-term warming trend.

Sure, there are differences. The summer-winter changes in insolation are much larger than those due to human-induced greenhouse gas changes; the seasonal change is mainly in the visible part of the electromagnetic spectrum while the greenhouse gas forcing is in the infrared; the greenhouse gas influence is global while the seasonal changes are opposite in the two hemispheres; and we have a much longer history of observing the seasonal changes, so a more or less correct prediction can be made empirically, without any physical understanding. But really, the basics are quite similar. So anyone who thinks a climate forecast can’t be done can benefit from thinking about what is behind the changes happening at this time of year.