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Hourly Records, Wind, and Weather Considerations (BFB, STFB & NTFB)
The weather station that a Fire Behavior Specialists selects for a Basic (BFB), Short Term (STFB) or Near Term (NTFB) Fire Behavior analysis generates the daily Weather Summary and associated Hourly Records. Precipitation amount, temperature, relative humidity, wind speed, wind direction and cloud cover are the hourly weather and wind inputs that are utilized by these three models.
Select a weather station where the Weather Summary shows daily maximum and minimum temperatures, relative humidities and precipitation amounts similar to those observed in the fire area over the last two or three days. Prior to initiation of the modeled fire, BFB and STFB condition dead fuels based on these values, as well as on topography, canopy cover, and cloud clover. NTFB conditions dead fuels both prior to the ignition and throughout the simulation.
Carefully review the Weather Summary and Hourly Records data and make adjustments as necessary by modifying hourly records.
Typically, the best station is the closest in terms of straight line distance and elevation to the incident (WFDSS defaults to this station.) Certain micro-climates, rain shadow effects, and other variables may require you select a station other than the closest one to the fire in order to better capture more representative weather for the conditioning and forecast (NTFB) periods. Recent rain recorded by the RAWS site, but not on the fire, can have a major impact on fuels conditioning. When this occurs, you may want to zero out the rainfall in the Hourly Records. Similar adjustments can be made to maximum humidities (if the RAWS station was under an inversion and the fire was in a thermal belt, for example).
Wind speed and direction values in the Hourly Records are not used by the BFB or STFB models. Instead, these two models use the static wind speed and direction in the Wind Information section. When viewing wind speed and wind direction inputs in BFB and STFB you will notice that these fields cannot be changed. NTFB, however, does adjust winds for each hour in the simulation burn period and, during these hours, the winds can be edited. With NTFB, it is important to consider winds at the weather station location in addition to weather. Some RAWS that are representative for weather may have terrain that funnels winds in directions that are not representative of the fire area.
After selecting a weather station and completing a run, review the 1-hour fuel moisture grid to see how the dead fuels were conditioned and if they are similar to the values that are observed in the fire area during the hours of interest.
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Last updated on 1/28/2019 2:08:50 PM.
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