Weather Forecasts and Smoke Management

Weather forecasts typically are produced twice each day and become available within 3 to 6 hours after 0000 UTC and 1200 UTC observations are complete. This is because prognostic models require input data from the 0000 UTC and 1200 UTC upper-air observations and a few hours of run-time on a super computer. Prognostic models (progs) form the basis of most forecast products. For example, the first forecast of the day should be available by 7 am to 10 am local daylight time from Anchorage and by 10 am to 1 pm local standard time from Miami. Earlier forecasts or forecasts updated throughout the day are possible if the most recently available upper-air observations and prognostic model outputs are combined with updated surface observations. While public forecasts issued by the National Weather Service and the media are useful, they typically lack the detail needed for smoke management. For this reason, spot-weather forecasts may be requested from state, federal, or private weather services that provide predictions of critical variables that influence smoke at specified times and locations.

Even though there are increasing numbers of numerical guidance tools, weather forecasting still is an art, especially in places with few observations or where there are complex local interactions with terrain, water bodies, and vegetation cover. The primary source of smoke weather forecasts remains the National Weather Service. Their rigorous training, fire weather program, and state-of-the art equipment and analysis tools help maintain a unique expertise. Most NWS fire weather forecast offices now issue special dispersion and transport forecasts. In addition to NWS forecasters, many states maintain a smoke management program with highly skilled meteorologists. Also, the number of inter-agency fire weather offices and private meteorological services is growing and can provide reliable forecast products specifically designed for smoke management. Whatever the source of a forecast, it is helpful to combine the forecast with your own general understanding of weather conditions by reviewing the many satellite pictures, current observation summaries, and prognostic model output products now available on the World Wide Web. In this way, apparent trends and local influences can be determined and the need for last minute changes can be recognized more quickly. For example, increasing afternoon cloudiness in the forecast may have indicated an approaching storm that was predicted for the following morning. If clouds do not increase when predicted, however, it could be suspected that the storm has been delayed or it was diverted elsewhere. A check with the forecaster or updated satellite picture may confirm the suspicion and the management plan may be altered.

Because the atmosphere behaves chaotically, the accuracy of a weather forecast improves as time to an event shortens. For example, it is possible to provide an indication of storminess within 30 to 90 days. A storm passage, however, may not be predicted until about 14 days in advance with about 2 days accuracy. Within 5 days, 1-day accuracy on storm passage may be possible. Increasing accuracy should be expected within 48 hours and the timing of storm passage within 1/2 hour may be possible with 12 hours advance notice. Spot weather forecasts usually are available 24 to 48 hours in advance of a scheduled burn. This allows a smoke manager to anticipate a potential burning window well in advance. Specific timing, however, should not be made before 2 days in advance if the situation is highly dependent on an accurate weather forecast.

Our increasing knowledge of air-sea interactions is making it possible to predict some aspects of weather up to a year in advance as certain regions of the country respond to the El Niño Southern Oscillation (ENSO). Precipitation and temperature during winter and spring are most strongly related to ENSO. Relating key factors for smoke management such as wind and mixing height or stability is more difficult, especially during summer. Nevertheless, an ENSO-based seasonal prediction gives prescribed burners an idea of general weather conditions to be expected, thereby helping prioritize scheduled burns and decide if marginal days or weekends early in the burning season should be used or whether a more optimum season will ensue.