The Relationship Between Extratropical Cyclone Steering and Blocking Along the North American East Coast

The path and speed of extratropical cyclones along the east coast of North America influence their societal impact. This work characterizes the climatological relationship between cyclone track path and speed, and blocking and the North Atlantic Oscillation (NAO). An analysis of Lagrangian cyclone track propagation speed and angle shows that the percentage of cyclones with blocks is larger for cyclones that propagate northward or southeastward, as is the size of the blocked region near the cyclone. Cyclone-centered composites show that propagation of cyclones relative to blocks is consistent with steering by the block: northward tracks more often have a block east/northeast of the cyclone; slow tracks tend to have blocks due north of the cyclone. Comparison with the NAO shows that to first-order blocking and the NAO steer cyclones in a similar manner. However, blocked cyclones are more likely to propagate northward, increasing the likelihood of cyclone related impacts. Plain Language Summary The path and speed of extratropical cyclones along the east coast of North America influence their societal impact. However, the factors that determine the path and speed of these cyclones are not completely understood. One weather pattern that is expected to have an impact is atmospheric blocking. Blocks are large, immobile, high-pressure systems. The work herein shows that cyclones that move slower than average are more likely to have a block due north of the cyclone center. Also, cyclones that take a path that is more toward the north as compared the typical path of cyclones are more likely to have a large block downstream. This analysis is useful because it shows the spatial relationship between the cyclones and the blocks. The analysis also shows that knowing where a block occurs relative to a cyclone provides unique details on northward moving cyclones, as compared to the basin-scale climate pattern that is most often used as a guide for considering extratropical cyclone movement.