FARSITE Weather Stream and Burn Periods

The Weather Stream and Burn Periods tab loads a weather stream and set burn periods. Both are required for a Farsite simulation.

The Weather Stream

Farsite requires a weather stream for the length of the simulation. You define this weather stream with a Weather Stream (.WXS) File.

Click the button to display several weather stream options,

• Open WXS File... - if you already have a Weather Stream (.WXS) File, use this option to load it into your simulation,
• Create WXS File... - you can create and load a new Weather Stream (.WXS) File for your simulation,
• Edit WXS File - once you have a weather stream loaded, you can edit the Weather Stream (.WXS) File.

Conditioning Period

Using the Weather Stream (.WXS) file Farsite will condition dead fuels during the simulation burn periods. You can set the Start of your conditioning period to the beginning of your Farsite simulation (the first burn period) but it is recommended to set the start of the conditioning period three or more days prior to the first burn period. Three days of conditioning are usually adequate for most simulations, but if there are significant 10 and 100 hour timelag  fuels in your landscape you may want to increase your conditioning period up to seven days prior to the first burn period. (1000 hour fuels are not used in Farsite simulations)

Once a Weather Stream (.WXS) file is loaded the Fuel Moisture Conditioning Start Day:  and Time: text boxes will be populated with the beginning and end dates/times of your weather file and you can select the conditioning period from that range.

Burn Periods

Burn periods are required for a Farsite Simulation and must fall in the date/time range of the loaded Weather Stream (.WXS) File.

Specific daily burning periods are required to be identified in a Farsite simulation. Burning periods can be up to 24 hours long but shorter periods can used to stop the simulation during periods of low activity, such as cool, moist nights or rainy periods. It helps correct the tendency of Farsite to over-predict under moderate burning conditions because long periods of very low fire behavior can result in significant spread distances.

This feature can also be used to speed up simulations by "turning off" the simulation during periods of low fire behavior that have little effect on the final results.

Burn Periods can be added in two ways,

• with the Edit WXS File option after clicking the button,
• using the Burn Periods group on the Weather Stream and Burn Periods tab (described below).

Initially no burning periods are identified, burn periods must fall in the range between the conditioning period start and the end of the weather stream. There are two buttons in the Burn Period group.

	Appends a new burn period to the list.
	Deletes the selected burn period from the list.

Clicking the button creates a burn period for the start day of the conditioning period.

NOTE: The Start Hour and End Hour are actual times, not burn period or perimeter labels. For example, an End Hour of 1900 and a 120 minute time step defines burning for 1700-1859 hours and burning ends at 1859. Similarly a Start Hour of 0800 with a 120 minute time step would record the first perimeter at 1000 hours.

Burn periods can be then edited by clicking in the appropriate field. Additional burn periods can be added with the button.