Weather Models May Be No Match for Climate Change.

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First off, let’s put it clearly. The sophisticated weather models used worldwide to forecast rain and snow failed once again to accurately predict Northern California weather. This has been the norm throughout this dry winter season.

Not only that, in terms of the Sunday rain event forecasted, they missed in the same way as previously. Namely forecasting significant rain and snow, then backing away from the prediction at the last minute. And it isn’t just one model missing. All of the major and minor models have been off in the same direction. Clearly something is up.

Here is the European medium range model prediction on April 19th, just 5 days before the storm’s arrival. (Image 1) An inch of rain for Sonoma County.

Two days later, 3 days before the storm, it was still on the bandwagon. (Image 2) The European is considered the gold standard for medium range weather prediction.

But all of the models were off. Here is the Weather Predication Center average of all of the major models on April 21st, 22nd and 24th. (Images 3, 4, 5) The last forecast, issued barely 24 hours before the storm’s arrival, still showing one half to one inch of rain for Sonoma County.

And even the short range mesoscale models, designed to provide the best high-resolution view of what’s to come, missed badly. For example the North American Model, showing six tenths to an inch of rain on the way barely 48 hours before the storm’s predicted arrival. (Image 6)

So, what’s going on? A few thoughts.

In terms of forecasting, weather prediction relies on complex computer driven algorithms, but in essence all are based on assumptions about how weather behaves. And these are based on past experience. Mainly thermodynamics and atmospheric physics. Weather behaves like a fluid system, say a river for example. A very complex river to be sure.

Add in varying amounts of heat and moisture, throw in other influences caused by the spinning planet, factor as well cyclic seasonal influences, and you have a mathematical result, one that ultimately leads to a forecast.

But with climate change there is much discussion that past assumptions may no longer be valid. The planetary machinery of heat and cold, pressure and momentum are not operating as in the past. Oceans are absorbing vast amounts of heat, ice sheets are melting, and tundra storage of carbon is being released in places like Canada and Alaska. In such a rapidly changing system, the first and greatest misses caused by now invalid assumptions would be where the real-time impact of climate change is already having the greatest impact. California is one of those places.

As we in the North Bay and Sonoma County prepare for another hot, dry summer, and drought restrictions, climate scientists are already examining whether past assumptions that impact weather prediction have to be modified. This is a major topic in the climate world, as is the trend in California to greater climate extremes. Daniel Swain, a prominent climate scientist at UCLA, is among those on the cutting edge of research. He and others are now predicting hotter, drier years punctuated by very wet, flooding years like 2017.

For us in the North Bay and the rest of California more accurate prediction won’t bring us more rain, or more moderate weather. But it will make planning and preparing for it an easier task for millions of citizens and policy makers who will have to adapt the state’s vast water supply system to a rapidly changing climate.

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