I have a new paper in this month’s issue of the journal Weather and Forecasting entitled “Impacts of a Storm Merger on the 24 May 2011 El Reno, Oklahoma, Tornadic Supercell“. In it, my coauthors and I investigated whether a particular instance of a smaller storm merging into a mature tornadic supercell (“Storm B” in the NWS nomenclature) was related to the “handoff” between tornadoes B1 and B2. The answer, for this particular case, was “No.”
I made a 12-minute presentation about the work behind this publication at the 27th AMS Severe Local Storms Conference in Madison, Wisconsin. To summarize, when we assimilated phased array radar (PAR) data into a model to retrieve the updrafts, I found that, despite the apparent union of the reflectivity contours just before the tornado handoff, the updrafts actually joined together about 10 minutes later, approximately 5 minutes after the tornado handoff. Therefore, we were not convinced that the merger caused the handoff in this particular instance. We speculated, because of the complexity of the interactions between the two storms, that not all storm mergers would proceed like this one. Our speculations align with a wealth of anecdotal storm chaser observations, wherein storm mergers are associated with a spectrum of outcomes ranging from apparent enhancement of to cessation of tornado production. A great deal of research remains to be done on the relationship between storm mergers and tornadogenesis.