So what is all this talk about La Niña and the bad weather predicted between now and spring?

To answer this and other questions, I visited the National Weather Service facility at the National Oceanic and Atmospheric Administration station in Seattle. Jay Albrecht, senior forecaster with 18 years on duty in Seattle, provided a look behind the scenes of a fascinating operation. It consists of sophisticated computer networks, data collection and talented professionals who interpret a constant flow of weather information.

How are forecasts arrived at?

There is a network of data collection that ranges from weather balloons to satellites and airborne passenger planes – and everything in between. This constant flow of information is fed to various computer models throughout the globe.

Vast amounts of data eventually arrive at five work stations at NOAA. Each has its specialty. The busiest are the Public Service/Quality Control desk, the Public Forecast desk and the Aviation/Marine Forecast desk.

Additional work stations are manned when there are special conditions influenced by weather. These include anticipated flooding, large, damaging storm systems, dry conditions that lead to forest fires and incidents like large oil spills.

What is so great about computer models?

Years of experience, lots of smart people and technological advances have determined that many atmospheric events are predictable. When wind speed and direction, surface and air temperatures aloft, humidity and a myriad of other data are known, short range weather predictions of up to seven days are fairly accurate.

Longer range predictions are a bit trickier to pin down. But various conditions like El Niño and La Niña are influenced by ocean temperatures that are known to impact local weather conditions. Such trends and their influence are fairly predictable months in advance, but are always subject to revision as conditions change.

How reliable are the models?

Many countries have developed their own models and may interpret weather data somewhat differently. Meteorologists can overlay satellite, radar and other data from the various models on computer screens. When this data matches fairly well, the degree of confidence is high. When it does not, confidence is lower and further investigation is emphasized.

How do the TV weather personalities use this information?

The media outlets use the boiled down information from NOAA to create their own weather forecasts and develop the colorful graphics we view on the evening news. Their degree of sophistication varies widely, but not all television weather persons possess the credentials and degrees in atmospheric sciences that a professional meteorologist does.

Back to the future – what is with this La Niña and bad weather talk?

La Niña conditions occur when ocean temperatures along the equator in the central and eastern Pacific are colder than normal. This situation has existed for several weeks and may create wetter and cooler weather that will be pushed up to the west coast of the United States.

Since these current ocean conditions have changed little, the earlier predictions of wet, cool and windy weather from January through March in the Pacific Northwest still hold true.

El Niño conditions exist when the ocean temperatures are warmer than normal. This causes warmer and somewhat drier winters and less windy conditions in our region.

Interestingly, when the ocean temperatures are normal, some of the most severe winter storms can occur. For example, those were the conditions during the ice and snow event of December 1996.

How does all of this affect your trees?

There is no magic formula for what predicted wind velocities will increase the odds of tree failures. We do know that saturated ground conditions, high wind gusts and root diseases increase the chances.

Albrecht mentioned that winds from the north and east, like those coming from the Enumclaw area, seem to cause tree failures at lower wind velocities than the usual winds that originate from the south and southwest. He speculated that many trees may be more wind firm and can withstand the higher gusts from the south.

I have noticed that some trees that have fallen during east winds had poor root development on their east sides. So there may be some truth to his observation.

Preparing for the worst conditions

If a homeowner is concerned about trees, it may be prudent to have a certified professional conduct a hazard assessment. Generally, the fears are unfounded, but if a tree near a worrisome tall fir, cottonwood or maple has recently fallen or appears to be unhealthy, caution is advisable.

Dennis Tompkins is a certified arborist, certified hazard tree assessor and Master Gardener from the Bonney Lake-Sumner area. He provides small tree pruning, pest diagnosis, hazard tree evaluations, tree appraisals and other services for homeowners and businesses. Contact him at 253 863-7469 or e-mail dlt@blarg.net. Website: evergreenarborist.com.