Overnight, people in Acapulco, MX found themselves in the midst of a Category 5 hurricane that no one had prepared for. As of this morning, there is still little information about the impacts, but they are expected to be potentially devastating.

Just twelve hours before Hurricane Otis made landfall in Mexico, it had been forecast to achieve Category 1 status — one fifth the strength it ended up achieving. Globally, governments spend hundreds of millions of dollars on weather forecasting. And yet in this case, they catastrophically failed. On a much smaller and less impactful scale, the same critical systems failed here in California last week.

Agriculture is just one of several important industries that depend heavily on accurate weather forecasting for making critical — although not life-or-death — decisions. Planting, harvest, pest control and other activities are entirely weather dependent.  In California, forecasting the first real storm of the Fall is particularly important: October is harvest season for many crops in the Central Valley, including canning tomatoes, nuts, and rice. A big storm will essentially put an end to those activities.  In particular this year harvest has been running late due to the cool weather in the spring that delayed crop maturity, and farmers have been racing to finish up harvest.

All last week, the official weather forecast for this area was for an unimpactful amount of precipitation: A few sprinklers or possibly a tenth of an inch that would cause a short delay in farming activities. So it was an unpleasant surprise for farmers to wake up on Sunday to a forecast of a quarter inch or more of rain.

But even that forecast, just a few hours prior to the system arriving, was dead wrong. The “Surprise Rain” continued all day and into the night in the Sacramento Valley, turning fields and orchards into a muddy mess. Terra Firma received a half inch of rain, but other areas just north and east of us received well over an inch.

To be clear, there was nothing catastrophic about this rain. On our farm, we did have alter our harvest plans for your boxes (see the “In your boxes” section for details). On farms that were still involved with harvesting walnuts and rice, it will cause a delay of several days. Any tomatoes that still needed to be harvested were lost, but they were at the very tail end of the season.

To the average person, the difference between a a half inch and a tenth of an inch of rain makes little difference, unless you had a big outdoor event planned. But to agriculture, the difference is simple math: it’s five times more rain.

I am not complaining in the least about the rain we received. It was just the right amount to settle 4 months worth of dust and wash it off the plants. And most of the crops growing at Terra Firma now — fall and winter vegetables and fruit — enjoy rain in moderation.

But it is sobering to think that our 21st century weather prediction systems still have such a large margin of error at a time when we arguably need them to be more accurate than ever.