In late October, wildfires ravaged 800 square miles in Southern California, claiming 10 lives and nearly 2,200 homes. Weather played a key role in fighting these fires. Fire weather meteorologist John Snook is the Predictive Services program manager for the U.S. Department of Agriculture's Forest Service in Northern California. Snook was deployed in the south to aid firefighting efforts.

What weather monitoring system were used during the Southern California wildfires?

For the Southern California fires we mainly monitored an array of [remote automated weather stations]. These are stand-alone weather-observing platforms that transmit their data to a satellite, which is then down-linked, processed, and distributed. A program called ROMAN [real-time observation monitor and analysis network] expedites the viewing of a lot of RAWS data in a short time, from stations over a great variety of elevations and wind-exposure. For Southern California, there were about 50 RAWS stations that we were watching closely. Other monitoring tools are weather radar, profilers, and satellite (visible and infrared bands).

Did your weather monitoring activities change when the wildfires started in Southern California?

The activities became more frequent and more focused, as we keyed in on the areas that had the large and fastest growing wildfires. A big part of the monitoring and prediction is recognizing the diverse effects that topography can have on the general wind patterns. These include channeling, Venturi effects, and eddying and turbulence to the lee side of prominent terrain features. We looked at all sorts of data more frequently than usual, including RAWS. We were keying in on the strength of the 10-minute averaged wind, the peak gusts of each hour, the relative humidity (both daytime minimums and poor overnight humidity recovery at night — typical in Santa Ana wind events). We also closely monitored smoke transport, speed and direction.

What effect did weather monitoring have on controlling the fires?

While it was still very windy and dry on Sunday and Monday, we were able to offer hope to the incident management teams that more favorable conditions for safely fighting these conflagrations would arrive in three to four days. By Monday (Oct. 22), managers were well briefed that winds, while still significant, would show a day-to-day decrease beginning Tuesday on the fires closer to Los Angeles and on Wednesday for those near San Diego. This helped the multiagency coordination group prioritize which large or damaging fires would receive increasingly scarce resources first. On individual fires, commanders could form strategies on which portions of a fire to attack first. This was because they knew when more favorable winds (lower speeds and directions shifting to onshore — from the ocean) would arrive, and how ultra-low humidity patterns would gradually moderate day by day.

What are some of the early warning signs you look for in weather when trying to predict wildfire potential?

There are longer-term, and/or background factors such as dry fuels, existing drought in area. The shorter-term factors include looking for areas of moderate or stronger sustained winds, low humidity (which is particularly troublesome if it stays low even at night), and where lower atmospheric instability is greatest. We also try and combine resource availability in with the weather and fuels information.

How successful were the weather monitoring efforts?

Forecasters were able to see the strength and significance of this event in terms of wind and low humidity five to seven days in advance, and with higher than usual confidence. Monitoring efforts were very successful; there was never a time when I felt unsure of what the weather was near the fire areas. That is thanks mainly to the RAWS network and ROMAN, because we could easily see the data in real time from a many stations.

What were some of the key lessons you learned from these fires that can help during the next incident?

Normally I work in Northern California, and was only in Southern California to help out during this major fire event. So for me personally, I had to rapidly become more familiar with details of Southern California mountain ranges, and the local effects produced by the terrain variations (passes, canyons, etc.) on the general Santa Ana wind flow. This will greatly reduce my learning curve next time.