Another approach to weather

JACK SHEBSON Jerusalem

I read with consternation – but understanding – the letter criticizing the state of weather forecasting in Israel (“A ‘forecast’ is just that,” November 22).

Certainly, there is a problem: Forecasts are made as if they are a form of entertainment, and not for the supply of useful information. On the other hand, while forecasts are often inaccurate, they are not necessarily wrong.

Reader Gordon Bloch wrote that on November 21, he enjoyed the weather in Netanya. But those in Tel Aviv did not – there was more than 30mm. of rain. More recently, it rained substantially in the Haifa area and in Gush Etzion, but much less elsewhere, if at all.

On the larger scale, though, forecasts are correct.

Forecasting for Israel is challenging because Israel is a small country that also has small-scale weather. Unlike in the US, where it can snow from Maryland to Connecticut, here it can snow in Jerusalem or Gush Etzion (or vice versa). Rarely, though, do we have storms large enough to cover the entire country.

A solution does exist: It’s called “ensemble forecasting,” in which multiple forecasts are made accounting for small-scale errors, and instead of a “yes” or “no” for rain, the chances are given as probabilities (high, medium or low, for example). This way, forecasters can account for what we don’t know while at the same time saying something useful. The user can then decide if he or she wants to risk leaving the umbrella at home.

This has been my approach for quite some time. BARRY LYNN Efrat The writer has a PhD in meteorology and is CEO of Weather It Is, Ltd.