Meteorological evolution of fire threat days over the Northeast U.S

While large wildfires are not as common in the northeastern U.S. as in the western U.S, they can still have a substantial impact. For example, the “Sunrise Fire” in the Pine Barrens region of eastern Long Island in August 1995 burned 7,000 acres, destroyed a house and 5 fire trucks, and damaged nine other houses and several businesses. Few studies have focused on fire weather forecasting over the Northeast United States. A small number of papers have focused on a synoptic weather classification of fire weather events just outside of the Northeast (West Virgina region) and have presented a limited number of case studies.

This presentation will describe the meteorological evolution associated with fire weather events over the Northeast U.S. The large-scale conditions that favor fire weather over the Northeastern U.S. were obtained using the archived fire danger days from the Wildland Fire Assessment System (WFAS) from 1998 to 2006. This study used the Yarnal (1993) classification scheme to denote five possible positions of surface high pressure systems for the various events, following an approach similar to that used in previous studies over the Virginias. The North American Regional Reanalysis (NARR) was also used to composite the meteorological conditions during days with an elevated threat of wildfires. In particular, the PBL height and the source of the dry air were investigated using NARR, and then compared to the climatological average.

Some preliminary results have been obtained over the Northeast U.S. during the spring period (March-May) for 30 events. About 60% of the fire threat days occur in April (only 3% in May). This is most likely due to the influence of dry continental air that frequently moves into the Northeast from Canada in April, the seasonal increase in radiative and sensible heat fluxes, and the pre-existing dead fuels (pre-green up period). For this period the most common (~35%) synoptic characteristic from Yarnal (1993) is the “pre-high,” which involves high pressure building towards the Northeast from the Great Lakes and Canada. Already dry northwesterly flow over the Northeast experiences additional drying as from downsloping off the Appalachians. For this presentation, the analysis will be extended for the full year and the composite results will be related to the 17-20 April 2008 case study, during which a fire burned over 3,000 acres in Minnewaska State Park Preserve near New Paltz, NY.

Reference:

Yarnal, B. 1993: Synoptic climatology in environmental analysis: A primer. Belhaven Press, London.