Trajectories are created by Gary Morris (Valparaiso University) using the NASA Goddard Trajectory Model (Schoeberl & Sparling, 1995) in kinematic mode driven by NCEP 1×1 meteorological fields in a combination of analysis and forecast modes. Trajectories are initalized 24 hours in the future, then run backward for 7 days.

500-m trajectories begin scattered from the Upper Midwest into Western Canada, coming together in the Dakotas (0 – 6 km) 5 – 7 days prior. The cluster then streams down the Great Plains into Eastern Texas (< 2 km) 0 – 3 days prior. The air mass spends the previous 24 hours along the Galveston – Louisiana Coasts – stagnant air. 1500-m trajectories stream into the Pacific Northwest and British Columbia 5 – 7 days prior, mainly 4 – 7 km. Most parcels gather in Minnesota and the Dakotas (2 – 4 km) 3 – 4 days prior. Most move down the Mississippi (2 – 3 km), arriving on the Gulf Coast 0 – 2 days prior – more stagnant air. 2500-m trajectories mainly stream into the Pacific Northwest 3 – 7 days prior > 4 km, while a second smaller groups comes ashore into Mexico and moves NNE into West Texas. The northern group descends down the Mississippi, with both groups arriving along the Gulf Coast 0 – 2 days prior from the N and NE. Again, the air mass is very stagnant.