High-Latitude Blocking: Pacific Precursors and High-Impact Weather

Large-scale flow pattern transitions can substantially influence US energy prices by altering surface temperature anomalies and thus anticipated consumer heating and cooling demands. Anticipating such pattern changes is therefore critical to firms such as Citadel that trade natural gas and electricity contracts.  A notoriously challenging pattern transition to predict is the onset of a blocking-type ridge (i.e., a quasi-stationary negative potential vorticity at the tropopause level), a feature frequently associated with surface weather extremes. This seminar will demonstrate the role of synoptic features such as recurving tropical cyclones and warm conveyor belts associated with extratropical cyclones as precursors to high-latitude blocking. A numerical modeling study (Grams and Archambault 2016) will be used to illustrate how diabatic upper-level outflow associated with tropical cyclone recurvature is dynamically linked to high-latitude ridge amplification. Additionally, a case study will be presented of the role of recurving Super Typhoon Nuri in the onset of Alaskan blocking and an unexpected cold air outbreak over the contiguous United States in November 2014. The analysis will include an evaluation of the skill of the ECMWF ensemble prediction system in predicting the US cold air outbreak and its upstream precursors.