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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

IBC Memo 24-01: OF 297 Signature Order and 2024 Fire Season Use IBC Memo 24-02: Summary of Changes for SIIBM, PMS 902

Date: July 15, 2024
Contact: Incident Business Committee 

The NWCG Incident Business Committee (IBC) has recently released two memorandums. The first provides direction on the use of the Emergency Equipment Shift Ticket, OF 297 for the 2024 fire season. Due to delays in hard copy printing, both the 2024 revision and the older version of the Emergency Equipment Shift Ticket, OF 297 are acceptable for use during the 2024 fire season.

The second memorandum documents the updates of the newly revised NWCG Standards for Interagency Incident Business Management (SIIBM), PMS 902. The summary of changes attached to the memo covers the major updates and process changes from the 2022 version.

References:

IBC Memorandum 24-01: OF 297 Signature Order and 2024 Fire Season Use

IBC Memorandum 24-02: Summary of Changes for the NWCG Standards of Interagency Incident Business Management, PMS 902

IBC Memorandum 24-02 Attachment: Summary of Changes

NWCG Standards for Rapid Extraction Module Support, PMS 552

Date: July 10, 2024
Contact: Incident Medical Unit Subcommittee 

A new publication from the Incident Medical Unit Subcommittee is now available. The NWCG Standards for Rapid Extraction Module Support, PMS 552 will be used as a guide and as an opportunity to begin to build out Rapid Extraction Module Support (REMS) modules for the remainder of Fire Year 2024. These standards will be fully implemented as the minimum standard starting in January 2025.

NWCG Standards for Rapid Extraction Module Support outlines the roles, duties, qualifications, and equipment pertinent to REMS. A REMS team, strategically stationed at wildland fires, plays a pivotal role in prioritizing swift access and medical treatment to injured or ill firefighters for safe and efficient egress off the fireline. This ensures their rapid transport to definitive medical care in cases of emergency during firefighting operations, highlighting the invaluable contribution of the REMS team to firefighter safety and well-being.

References:

NWCG Standards for Rapid Extraction Module Support, PMS 552

National Wildland Firefighter Day

Date: July 2, 2024
Contact: National Interagency Fire Center 

The National Wildfire Coordinating Group (NWCG) would like to recognize July 2, 2024, as National Wildland Firefighter Day (NWFFD). Established in 2022, NWFFD honors the dedication of wildland firefighters and support personnel. This day falls within the 2024 Week of Remembrance (June 30 - July 6), providing an opportunity to renew our commitment to wildland firefighter safety while remembering those who have fallen in the line of duty.

NWCG continues to provide leadership to enable interoperable wildland fire operations among federal, state, local, Tribal, and territorial partners. NWCG standards and training establish common practices to contribute to safe, effective, and coordinated national interagency wildland fire operations.

References:

NWCG.gov

Week of Remembrance

National Wildland Firefighter Day

2024 Week of Remembrance

Date: June 27, 2024
Contact: 6 Minutes for Safety Subcommittee 

As we approach the 2024 Week of Remembrance (WOR), June 30 to July 6, we dedicate this time to thoughtfully reviewing and recognizing the events of the 2018 Mendocino Complex. As such, this year’s theme of “Learning From the Mendocino Complex” embodies a longstanding hallmark of WOR, honoring through learning.

Throughout the week, our energy will be directed toward fostering generative conversations in briefing rooms and at tailgates.

References:

6 Minutes for Safety - 2024 Week of Remembrance

Wildland Fire Lessons Learned Center