Skip to main content

Firefighter Math: 8.2 Midflame Windspeed

Midflame windspeed (MFWS) is defined as the velocity of the winds, in miles per hour (mi/hr), taken at the mid-height of the flames. MFWS will directly affect the direction of movement of the flaming front and is important in fire spread calculations. The midflame windspeed is determined by use of the wind adjustment table, which provides values in terms of fuel overstory exposure and fuel model. 
table showing adjustment factors for different fuel shelterings

Figure 8.2 Adjustment factors for midflame winds.
The adjustment values are typically applied to the 20-foot windspeed, which is the speed that is measured 20 feet above any fuel or obstruction, usually by a weather station. The midflame windspeed is obtained by multiplying the 20-foot windspeed by the appropriate wind adjustment factor from the table. 

graphic showing different fuel shelterings

Figure 8.3 Effects of fuel sheltering on wind speeds.
It is very important to know which fuel model and sheltering configuration is being studied, and whether a given windspeed is a 20-ft windspeed or an already adjusted midflame windspeed. 

graphic showing friction effects slowing wind

Figure 8.4 Typical fuel sheltering for slope locations.
The midflame windspeed will be LESS THAN the 20-foot windspeed, because vegetation and friction slow down winds closer to the surface. That is why all the adjustment factors in the table are less than 1. 

Example 1 - A fire is burning in a fully sheltered area of dense, or closed, stands described as Fuel Model 4. The local weather station reports the 20-ft windspeed is 15 miles per hour. What is the midflame windspeed? Show all work on the wind adjustment worksheet (see below).

Solution - The figure above describes wind reduction factors and is used to determine the appropriate correction factor.

Step 1. The correction factor is 0.1 for any fuel model under fully sheltered conditions with dense stands.

Step 2. To find the midflame windspeed, multiply the 20-foot windspeed by the adjustment factor.
midflame windspeed =
20-foot windspeed × adjustment factor

MFWS = 15 mi/h × 0.1 = 1.5 mi/h

Example 2 - A 20-foot windspeed at the top of the ridge is reported to be 35 miles per hour, with fuel model 11 vegetation. What is the midflame windspeed? 

Step 1. See figure 8.4. The top of a ridge is indicated to be unsheltered.

Step 2. From figure 8.2, the adjustment factor is 0.4.

Step 3. MFWS = 35 x 0.4 = 14 mi/h

The values can be summarized in a wind adjustment worksheet. 
graphic of completed wind adjustment worksheet

 

NWCG Latest Announcements

NEW! S-390, Introduction to Wildland Fire Behavior Calculations (Blended) Available Now

Date: December 22, 2025
Questions about RT-130? 
Please contact: Fire Behavior Subcommittee

NWCG is excited to announce that the new S-390, Introduction to Wildland Fire Behavior Calculations (Blended) training is now available on the Wildland Fire Learning Portal.

This third course in the series combines online and instructor-led training components aimed at individuals who are involved in planning, managing, and executing wildland fire and prescribed burn operations; who require a thorough understanding of fire behavior calculations to enhance effectiveness and safety. This includes students who require the knowledge and skill necessary to perform the duties of a Type 3 Incident Commander (ICT3), Division/Group Supervisor (DIVS), or Prescribed Fire Burn Boss Type 2 (RXB2).

Students are required to be qualified as any Single Resource Boss position and complete the prerequisite S-290, Intermediate Wildland Fire behavior (Blended) course, before enrolling in S-390.

References:

S-390, Introduction to Wildland Fire Behavior Calculations (Blended)

Wildland Fire Learning Portal

NEW! S-320, Introduction to Incident Management Teams (Blended) Available Now

Date: December 18, 2025
Questions about RT-130? 
Please contact: Incident and Position Standards Committee

NWCG is excited to announce that S-320, Introduction to Incident Management Teams (Blended) is now available on the Wildland Fire Learning Portal!

This blended course combines online learning with instructor-led training, designed for individuals seeking to build leadership skills and gain experience in incident management.

Students are required to complete the prerequisite trainings ICS-100, Introduction to Incident Command System (ICS), ICS-200, Basic ICS for Initial Response, and ICS-700, An Introduction to the National Incident Management System (NIMS) prior to attending S-320.

References:

S-320, Introduction to Incident Management Teams (Blended)

Wildland Fire Learning Portal

New! Ransom Road WFSTAR Module

Date: December 16, 2025
Questions about RT-130? 
Please contact: NWCG Audiovisual Specialist

NWCG is excited to announce the release of the new Ransom Road Fire Module to RT-130, Wildland Fire Safety Training Annual Refresher (WFSTAR).

This module features a firsthand account from Rob Lee, official reports, and animated maps of the Ransom Road Fire which occurred on June 8, 1981, in Florida's Merritt Island National Wildlife Refuge.

The module is available now in NWCG's RT-130, WFSTAR Catalog.

References:

WFSTAR Catalog

Wildland Fire Lessons Learned Center

Call for Nominations: Paul Gleason Lead by Example Award

Date: December 11, 2025
Questions? Please contact:
 Leadership Committee 

Do you know someone working in wildland fire who strives to make positive change and is undeterred by obstacles or setbacks? Now is your chance to give that person the acknowledgment they deserve by nominating them for a Paul Gleason Lead by Example Award.

This award, is presented by the NWCG Leadership Committee to remember Paul Gleason's contributions to the wildland fire community and to recognize individuals or groups that exhibit the same spirit and dedication to leadership – those who lead by example.

Nominations can be submitted via email with an attached Lead by Example Form to BLM_FA_Leadership_Feedback@blm.gov or through the online form. 

Tips for successful nominations and more information can be found on the Lead by Example webpage. All nominations must be submitted by December 31, 2025.

References:

Paul Gleason Lead By Example Award 

Paul Gleason Lead by Example Award Nomination Form 2025 

Leadership Committee