Thursday, 15 December 2011

Fire weather

Supporting national, regional and local land management agencies such as the US Forest Service, the NWS issues a complete Fire Weather Forecast twice daily, with updates as needed. The forecast contains weather information relevant to fire control and smoke management for the next 12–48 hours. The appropriate crews use this information to plan for staffing and equipment levels, the ability to do prescribed burns, and assess the daily fire danger. Once per day, NWS meteorologists issue a coded fire weather forecast for specific USFS observation sites that are then input into the National Fire Danger Rating System (NFDRS). This computer model outputs the daily fire danger that is then conveyed to the public in one of five ratings: low, moderate, high, very high, or extreme.

The local weather office also, under a prescribed set of criteria, will determine if a Fire Weather Watch or a Red Flag Warning needs to be issued. These products alert not only the public, but other agencies that conditions are creating the potential for extreme fire behavior.

On the national level, the NWS Storm Prediction Center issues fire weather analyses for days one and two. These include large-scale areas that may experience critical fire weather conditions including the occurrence of "dry thunderstorms." These are thunderstorms, usually occurring in the western U.S., that are not accompanied by any rain due to it evaporating before reaching the surface.

NWS IMET taking observations in the field
State and Federal forestry officials sometimes request a forecast from a WFO for a specific location called a "spot forecast." Spot forecasts are used to determine whether it will be safe to ignite a prescribed burn and how to situate crews during the controlling phase. Officials send in a request, usually during the early morning, containing the position coordinates of the proposed burn, the ignition time, and other pertinent information. The WFO composes a short-term fire weather forecast for the location and sends it back to the officials, usually within an hour of receiving the request.

The NWS assists officials at large wildfires or other disasters, including HAZMAT incidents, by providing on-site support through Incident Meteorologists (IMET). IMETs are NWS forecasters specially trained to work with Incident Management Teams during severe wildfire outbreaks or other disasters requiring on-site weather support. IMETs travel quickly to the incident site and then assemble a mobile weather center capable of providing continuous meteorological support for the duration of the incident. The kit includes a cell phone, a laptop computer and communications equipment, used for gathering and displaying weather data such as satellite imagery or numerical forecast model output. Remote weather stations are also used to gather specific data for the point of interest. They often receive direct support from the local WFO during such crises. IMETS can be deployed anywhere a disaster strikes and must be capable of working long hours for weeks at a time in remote locations under rough conditions. There are approximately 70 to 80 IMETs nationally.