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Tuesday, April 23, 2013

YNP: Wawona Northwest Prescribed Fire Ignition Ops Completed. Expect Smoke #Yosemite #CaFire

Update 4-24 0800: Fire crews are continuing mop-up activities along the fire perimeter. For safety concerns residents and visitors are asked not to hike into or along the fire perimeter.  Hazards include hot stump holes, ash, snags (sanding dead trees) and falling fire damaged limbs.  

Lee Tarnay, Ph.D., Yosemite National Park Air Quality Specialist, has included a few items to note:
There was good dispersion and mixing of smoke during the day.

Nightime smoke stayed at the level it was emitted (midslope) and then moved downslope with the large scale downsloping winds, that occur in the Sierra on most calm nights.

Cloud formation appeared to be enhanced in the humid air above the fire on the second day of ignitions.  This is due to smoke particles provide extra places for water vapor in humid air to condense, called nucleation; just as a glass of water gets condensation on a hot day. 

Wawona Northwest Prescribed Fire ignition operations

Wawona Northwest Prescribed Fire
April 23, 2013

Yosemite National Park firefighters conducted two days of ignition operations and completed the 150 acre Wawona Northwest Segment B Prescribed Fire Monday evening, April 22.   Firefighters have begun mop-up activities to secure the fire perimeter. Those actions may include burning out of interior islands and pockets of unburned fuel that could flare up and threaten existing fire perimeter lines. Active burn down will last 1 – 2 weeks.  Community members and visitors will continue to observe crews from various federal and state agencies conducting mop-up operations.  

The primary objective of the prescribed fire was to reduce hazardous fuels within the mixed conifer forest adjacent to the Wildland Urban Interface (WUI) community of Wawona.  This project creates a continuous area of reduced fuel by linking together multiple previous fires and treatments including the 2007 and 2008 Wawona Northwest prescribed fires, the 2007, lightning caused, Jack wildfire, and a series of mechanical vegetation thinning projects in the 2000’s.

A secondary objective is ecosystem restoration.  Applying fire under prescribed conditions mimics the frequent, low intensity lightning caused fires that occurred in Sierras prior to the exclusion of fire which began over 100 years ago under aggressive fire suppression policies. Historically, natural fire burned an average of 16,000 acres annually in Yosemite and played an integral role in shaping Yosemite’s ecosystems.  In the absence of frequent fire, unnatural levels of forest biomass have accumulated which has put many of Yosemite’s values at risk, including neighboring communities, and natural and cultural features.  As climate changes, these values become increasingly vulnerable to catastrophic wildfire.

Smoke will be present during the mop-up activities particularly during late evening and early morning hours.  Smoky conditions will diminish each day as the fire area cools. Fire managers will continue working with the Mariposa County Air Pollution District (MCAPCD).  A burn permit was issued to the park by MCAPCD prior to the start of ignitions.  Smoke monitoring equipment was installed within the community and will continue to be monitored.  Community members who are sensitive to smoke may want to close their windows and doors during the evening hours in order to reduce their exposure.

Photo: Attached is a photo showing the various fire crews working on this Prescribed Fire project from Whiskeytown National Recreation Area, Sierra National Forest, North Lake Tahoe, Point Reyes National National Seashore and Yosemite National Park.  

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****REMINDER**** Every fire has the ability to be catastrophic. The wildland fire management environment has profoundly changed. Growing numbers of communities, across the nation, are experiencing longer fire seasons; more frequent, bigger, and more severe, fires are a real threat. Be careful with all campfires and equipment.
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