Mesoscale model simulations of the meteorological conditions

Mesoscale model simulations of the meteorological conditions during
the 2 June 2002 Double Trouble State Park wildfire
Joseph J. CharneyA,C and Daniel KeyserB
USDA Forest Service, 1407 S. Harrison Road, Room 220, East Lansing, MI 48823,
Department of Earth and Atmospheric Sciences, University at Albany, State University
of New York, Albany, NY 12222, USA.
Corresponding author. Email:
Abstract. Late in the morning on 2 June, 2002, an abandoned campfire grew into a
wildfire in the Double Trouble State Park in south-central New Jersey. The wildfire
burned 1,300 acres, forced the closure of the Garden State Parkway, and caused an
estimated $400,000 in property damage. Although there were dead fuels on the ground at
the time of the fire, due to a late spring frost, the meteorological conditions at the time of
the fire were conducive to erratic fire behavior and rapid fire growth. Surface
meteorological observations indicate a profound change in surface atmospheric
conditions between morning and early afternoon of 2 June, resulting in a substantial drop
in relative humidity accompanied by an increase in surface wind speed in the vicinity of
the wildfire. Atmospheric conditions aloft indicate a synoptic-scale trough and an upper
level jet streak moving through the eastern United States during the time period. Satellite
imagery diagnoses the presence of a ribbon of middle-tropospheric dry air, skew T–log p
soundings suggest a deepening mixed layer, and wind profiler observations reveal mixedlayer wind variability. The surface drying and wind variability is hypothesized to result
from coupling between a deepening mixed layer and dry, high-momentum air in the
middle troposphere that leads to the downward mixing of dry air and high momentum
into the mixed layer, which in turn contribute to the observed erratic fire behavior. A
mesoscale numerical weather prediction model (MM5) is employed to resolve the
meteorological conditions at the wildfire location, as well as the features that precede and
accompany the observed weather and fire behavior. The simulation reveals a series of
episodes wherein dry, high momentum air aloft mixes down to the ground and
contributes to sudden drying and wind variability at the surface. The transitory nature of
the features diagnosed in the simulation suggests that coupling between the surface and
dry air aloft can have considerable spatial and temporal variability. Maps of the Haines
Index and Ventilation Index show that the above-ground processes associated with the
erratic fire behavior in this case are not detected by either index, suggesting that new fire
weather indices that are sensitive to the meteorological conditions documented in this
case could improve fire weather forecasts of similar events.
Additional keywords: fire weather, fire weather forecasting, wildfire.