Toward a rule-driven model for winds over complex terrain for fire spread modeling

The rule-driven wind model (MWM) for simulating winds near the ground over complex terrain has been extended from one to four rules. The first rule replaced mountains with a first-order pressure function that simulates flow induced by transient weather systems passing over complex terrain in a neutral atmosphere. The new rules add in impacts of stability and slope flows caused by nocturnal cooling and daytime heating.

Comparisons between MWM and time series of observed winds at wind recording sites in southern California were made for two cases: 26 October 2006 (Banning Pass, San Gorgino/San Jacinto Mountains (Esperanza Fire)) and 26 May 2010 (San Gabriel Mountains). The stability rule introduces the resistance of the atmosphere to vertical displacements. Results show the stability rule has little impact on wind direction but does reduce wind speeds to values closer to observed wind speeds.