Use the Worksheet below to calculate midflame wind speeds (Taken from NWCG Fireline Handbook Appendix B)
Input
Line A: 20-FT Windspeed, mi/h______
Line B: Wind Adjustment factor (Use the table at the bottom of the page)__________
Output
Line A X Line B = Midflame windspeed
Example: You have a 20-ft windspeed of 25 miles per hour, in unsheltered fuels and a fuel model 4. Based on this, the wind adjustment factor would be 0.5.
25 x 0.5 = 12.5 miles per hour midflame windspeed.
| Fuel Exposure | Fuel Model (1-13) | Adjustment Factor |
|---|---|---|
| Unsheltered Fuels: Fuel exposed directly to the wind. No or sparse overstory. Fuel beneath timber that has lost its foliage; fuel beneath timber near clearings or clearcuts; fuel on high ridges where trees offer little shelter from the wind. |
4, 13
|
0.5 |
| Unsheltered Fuels | 1,3,5,6,11,12, (2,7)1, (8,9,10)2 | 0.4 |
| Partially Sheltered Fuels: Fuel beneath patchy timber where it is not well sheltered; fuel beneath standing timber at midslope or higher on a mountain with wind blowing directly at a slope. | All Fuel Models | 0.3 |
| Fully Sheltered Fuels: Fuel sheltered beneath standing timber on flat or gentle slope or near base of mountain with steep slopes. | All Fuel Models |
Open Stands 0.2 Dense Stands 0.1 |
|
1 Fuels usually partially sheltered 2 Fuels usually fully sheltered |