Saturday, September 13, 2014

Saturday, September 13, 2014 - Meadow Fire - Yosemite NP

Smoke Impact Report – Yosemite National Park, September 13, 2014

Prepared by Mike Beasley (USDA-FS) and Gary Curcio (IPAFES)

A)    Key Points for Consideration:

·         The Meadow Fire grew only 27 acres yesterday based 10:36pm IR flight yesterday evening.
·         The Star King Fire is 9 acres in size, and the decision was made yesterday to suppress that fire, as it is only ½ mile from the Meadow Fire and has shown increasing activity.
·         The Cathedral Fire is 12 acres in size and the Lembert Fire is 2 acres in size.  Both are showing minimal activity and are at high elevation along the Tioga Road.  The Cathedral Fire is visible from the Tioga Road.
·         Some minimal burnout was conducted last night on the south end of the fire near Cathedral Cliffs and may not have been captured in the early evening IR flight.
·         The 24-hr average PM2.5 concentrations in Yosemite Valley dropped out of the Unhealthy for Sensitive Groups AQI range for the first time yesterday afternoon, since the large fire growth on September 9th. The 3-hr rolling average value for PM2.5 briefly dropped into the Good AQI range this afternoon.  Conditions are forecast to show continual improvement.
·         Conditions for rapid fire growth are still in place.  Should the Meadow Fire escape containment efforts and spread in alignment with wind and the only substantial pocket of timber to the northeast, smoke concentrations will increase dramatically. Generally, fires above 8500 ft. in elevation do not show significant fire spread, however drought conditions and lack of snowpack last winter could cause anomalies in this rule-of-thumb
·         Due to poor transport winds and radiational cooling over the fire at night, nighttime smoke will continue to settle down the Merced River drainage, reaching at least as far as Mariposa, and will likely cause light haze in Mariposa and other Sierra Foothill communities as the smoke lifts out of the drainage in the late morning to early afternoon.  Monitors are not showing any concentrations that would be a health concern. 
·         Southerly winds are forecast to continue through the weekend and into early next week resulting in a fairly predictable pattern of smoke impacts each day through the period. 

Figure 1: Infra-red flight data from 10:36 on 9/12/2014 showing fire growth on the Meadow Fire. The image on the right shows the fire progression.  This clearly shows the two days of significant growth on Sept. 8th and 9th.  Spread on the 9th was under the cloud cover from remnants of Hurricane Norbert, eliminating the primary spread mechanism of torching trees and spot fire propagation.  Much of the spread on the 9th was likely spot fires burning together in heavy fuels that remain critically dry (< 10% TLFM)  Significant portions of the perimeter were checked by granite domes, aiding subsequent suppression actions.

 Figure 2 BlueSky 2km model prediction of surface smoke concentration for 0602 on 9/14/2014. The model is predicting the smoke settling into the Merced River drainage.  This smoke lifts out of the canyon each morning producing haze near foothill communities. The outputs are modeled concentrations of Particulate Matter 2.5 (PM2.5) and are displayed in shades of pink/red.

Figure 3 BlueSky 2km model prediction of surface smoke concentration for 1812 on 9/14/2014. The model is predicting the smoke moving east with light diurnal upslope afternoon winds.

Figure 4 Photograph from Sentinal Dome looking east into the fire area at 1600 hrs. showing only a few pockets of smoke generation.

B) Past and Current Conditions:

Yesterday Morning smoke in the Merced River Canyon was lifted out around noon in most places. This lingering nighttime diurnal smoke caused light general haze in the Sierra Foothills. Yosemite Valley began the day in the Unhealthy for Sensitive Groups AQI range for PM 2.5 concentrations (rolling 24-hr. average), but dropped into the Moderate range by midday.  A few surrounding monitoring sites recorded Moderate AQI values in the morning.  By late afternoon light upslope winds moved smoke from the Meadow Fire into the Yosemite high country and over the Sierra Crest impacting the Devil’s Postpile site by late afternoon. By evening smoke had begun settling back into the Merced River Drainage. Minimal smoke concentrations also have been entrained in the nearby Tuolumne River drainage to the north of the fire.

Today Persistent high pressure created similar smoke movement, however decreasing fuel consumption manifested noticeably improved morning visibility in Yosemite Valley.  All but the Devil’s Postpile site began the day in the Good AQI range for 24-hr. PM 2.5 concentrations. The 24-hr. average concentrations in Yosemite Valley stayed in the Moderate range and decreased significantly throughout the day.  Even the 3-hr. rolling average particulate concentrations dipped briefly into the Good AQI range in the afternoon, and will likely stay there, except for tomorrow morning.

Tomorrow Smoke transport will be similar to today, however 24- and 3-hr. PM 2.5 concentrations are forecasted to improve, so long as suppression efforts are successful. Firefighters continue to face increasing winds, poor overnight humidity recovery, and near single-digit daytime relative humidity.  Any Smoke concentrations in nearby communities should remain in the Good 24-hr AQI range throughout the day.

Table 1: Observed and forecast 24- and 3-hour rolling average Air Quality Index (AQI) values for Sept.12th (observed), Sept 13th (forecast) for communities with air quality monitors.
Figure 5 Map showing location of particulate monitoring sites around the Meadow Fire.

Table 2: AQI Category interpretations as to meaning and actions to consider on order to protect.

For those wishing to view the last 15 days of hourly and 3 hour rolling average readings or hourly and the 24 hour rolling average for PM2.5 concentration plotted against the AQI for the Meadow Fire, please click here to view Yosemite Valley EBAM values.

Additional graphical information can be viewed for all PM2.5 Stations by clicking on the following document:

Check out the California Smoke Blog


Feel free to contact us:
Mike Beasley
Gary Curcio

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