Keeping an eye on the storm

By JAY GOETTING, Register Staff Writer

Weather is the intelligence piece of flood forecasting, according to Neal O'Haire, Napa County's emergency services manager.

When homes and businesses put out sandbags as early as the first of the new year, they're likely to remain visible for months. That's because the art -- or the science -- of long-range forecasting remains tenuous at best.

The rainy season isn't over until April, and there's no shortage of ideas on how much precipitation to expect between now and then.

Most forecasting agencies don't go out on a limb for long term forecasts beyond a month, and many don't even go that far. There are a few that claim to have the inside track on long-range meteorological prognostication.

The American Meteorological Association warns however, "No verifiable skill exists or is likely to exist for forecasting day-to-day weather changes beyond two weeks. Claims to the contrary should be viewed with skepticism."

O'Haire agrees with that. He relies heavily on the old standby, the National Weather Service, and consults the California Nevada River Forecast Center regularly.

Most forecasts are reliable when looking out 24 hours. Computer models allow a pretty good five-day outlook.

"It's one of those strange things. I'm not sure we're much beyond the Farmers Almanac," said O'Haire.

The Old Farmers Almanac foresees heavier than usual precipitation in mid-January, early to mid-February and mid-March.

A Web site for Dryday Systems boasts an 85 percent accuracy rate and says Jan. 16-25 has a low chance of heavy rain, while Jan. 27 to Feb. 2 will see a high amount of rain.

LongRangeWeather.com predicts a wet April.

One service gives ground saturation levels as well, and with current rates at 95 percent or higher, it doesn't take much rain to flood low-lying areas. It also says there is an above normal chance of heavy rains for the duration of the season.

Services that predict weather trends rely heavily on historic data.

Also important to the process are oceanic conditions. O'Haire said he keeps an eye on the west to see what's brewing in the Pacific as well as where the jet stream is. On Thursday morning it was over Seattle, well out of harm's way for the Napa Valley. On New Year's Eve it ran right through the Bay Area.

When circumstances warrant it, O'Haire participates in daily conference calls with meteorologists giving their best forecasts on a regional basis.

Computer models are widely used, and one British-based site even takes into consideration solar activity. An overview of the Internet site indicates that long range forecasting is mostly a U.K. phenomenon.

The American Meteorological Society sums it up: "Long-range forecasts are not as accurate every season as short-term forecasting is every day, but they definitely do have skill, and using them over a period of time will prove to be better than going on historical data alone. Better education and understanding of the capabilities of this science is necessary for wider acceptance and use of long-range weather forecasting."

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