Piecewise Potential Vorticity Inversion Analysis of an Explosively Deepening Diabatic Rossby Wave

A case of extremely rapid extratropical cyclogenesis over the northeast Pacific Ocean in late November 2019 is explored using a piecewise potential vorticity (PV) inversion perspective. The development of this storm is of particular interest as a majority of the strengthening occurred in an unusual environment characterized by cold sea surface temperatures. The development began as a weak but stationary upstream surface low in the north-central Pacific ushered high tropical air poleward towards a pre-existing surface frontal boundary, resulting in intense lower-tropospheric frontogenesis. This frontogenesis triggered a thermally direct vertical circulation mobilizing a diabatic Rossby wave (DRW) which then moved eastward along the baroclinic zone. An intensifying upper-level jet/front system draping equatorward from Alaska then became favorably aligned with the low-level DRW on its approach towards the California-Oregon border to force deepening rates as high as 4 mb hr^-1 just prior to landfall.

Analysis of this storm provides an opportunity to interrogate explosive DRW development over a cold ocean current. The analysis centers on piecewise potential vorticity (PV) inversion to recover the contributions of various physical processes to the 950 hPa geopotential height falls that characterized the storm. The PV analysis is complimented by a quasi-geostrophic omega perspective on the development that points to a leading role for the upper-level jet/front system involved in the evolution.