92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 1:45 PM
Using Atmospheric Trajectories to Analyze the Ingredients Associated with Heavy Winter Precipitation in Central North Carolina
Room 354 (New Orleans Convention Center )
Christopher M. Fuhrmann, Southeast Regional Climate Center (SERCC), Chapel Hill, NC; and C. E. Konrad

Winter precipitation is a major forecast challenge across the Southeast United States. Many winter storms in the region are often near a tipping point with regard to temperature, meaning that subtle changes in the vertical thermal profile can lead to significant changes in precipitation type and intensity. A backward (upstream) trajectory analysis was conducted for 15 winter storms (8 snow storms and 7 ice storms) to diagnose the transport of air and moisture into the region of heavy winter precipitation across central North Carolina, as well as provide estimates of adiabatic and diabatic contributions to the resulting thermodynamic profile. Analysis of atmospheric trajectories, as opposed to relative wind vectors or streamlines, is useful for tracing the spatial and temporal evolution of vertical motion, moisture transport, and temperature fields, as well as identifying key source regions for these ingredients. NOAA's Air Resource Laboratory's Hybrid Single-Particle Lagrangian Integrated Trajectory tool (HYSPLIT) was used to produce the trajectories based on two versions of the Eta Data Assimilation System dataset. Results of the trajectory analysis reveal that air arriving at the 850 hPa level (the level used to discriminate between freezing and frozen precipitation) in the region of heavy precipitation had descended anticyclonically from the Great Lakes to a position near the Gulf Stream off the Carolina coast. Air parcels that descended into the marine boundary layer (less than 1 km AGL) over the Gulf Stream waters were diabatically warmed by as much as 20C, resulting in sufficient warming aloft for freezing rain to be observed at the surface. Air parcels that remained above the marine boundary layer and/or were located north of the Gulf Stream were warmed only an additional 2C, resulting in a subfreezing atmospheric column supportive of heavy snow.

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