# Presentation: 069636

## Piedmont National Wildlife Refuge

- March 25, 2003
- Smoke Simulation Analysis
- Gary L. Achtemeier
- USDA Forest Service
- Athens, GA

## Task Description

- The following set of slides summarize a PB-Piedmont post-burn analysis of smoke movement in the aftermath of a 1085 acre prescribed burn conducted by the Piedmont National Wildlife Refuge. The burn was conducted on 25 March 2003. The model simulations run from 1600 EST 25 March through 0800 EST 26 March.

## Weather

- Weather during the burn was clear and dry with strongly dominant synoptic forcing. Synoptic forcing favored winds blowing from the southwest during the day and from the south at night. The surface geostrophic wind, a measure of the strength of the synoptic forcing ranged from 8-14 m/sec and the pressure field was oriented to favor winds blowing from the south. Synoptic winds of 8-14 m/sec blowing during the day, could produce winds of 16 – 28 knots – stronger than allowed by prescription. Observed winds during the night of March 25-26 were from the south at 2-4 m/sec. Turbulent down-mixing with air aloft would be expected to wash out any drainage layer that would be set up. Thus, the expected effect of drainage forcing, if any, is  channeled winds through valleys.

## Modeling Information

- PB-Piedmont Version 3.0-2003
- Grid spacing = 60m
- Domain size = 18.2x20.4 km
- Visual domain = 13.1x9.5 km
- Weather data: Hourly METAR
- Elevation data: USGS 30 m DEM

## 1700 EST 25 March 2003 PNWR

- The modeled location of smoke on the ground at 1700 EST  under strong synoptic forcing. Grid spacing is 60 m. maximum elevation difference is about 150 m. Actual burn site outlined by orange polygon. White numbers denote observation sites. Note that the burn site is north of Juliette Road (blue line along which most numbers appear).

## 0500 EST 25 March 2003 PNWR

- During this period synoptic forcing favored winds blowing strongly from the south. Model smoke placed across Juliette road along the south edge of the burn site is not valid because the burn site was north of the road. Smoke observations were taken beginning at 0530 26 March. Moderate smoke density was found along the road as marked by the red dashed line.

## 0600 EST 25 March 2003 PNWR

- Observations of smoke continued through the next hour. Most observations were taken along the Juliette Road just south of the burn site. Reports of “moderate smoke” were made along the solid red line. Also, light smoke was observed “in the trees” above the road between 9 and 10. This minor gap in the ridge would have ventilated the valley to the south.

## 0700 EST 25 March 2003 PNWR

- Mixing after sunrise began to disperse the smoke. At 0645 EST, smoke was still found at the Falling Creek bridge (triangle).

## 0800 EST 25 March 2003 PNWR

- Observations north of the burn site found smoke at three sites (circles) between 0830 and 0845.  Smoke was also found near Juliette Road east of the burn site (triangle).

## Summary

## Summary

- PB-Piedmont never simulated smoke along the road to the south of the burn site nor at Falling Creek Bridge. The presence of model smoke over the road south of the burn site was the result of a spurious location of the model grid over the road.
- PB-Piedmont never simulated smoke where smoke was observed points 9 and 10 on the  0700 EST image nor at point 17 on the 0800 image. One would have to consider the possibility that this smoke was from a site located to the south and that smoke originating there was channeled up stream valleys and over the road through gaps in the ridge.

- Summary