Climatology of inverted troughs over the gulf of Maine
Cebulko, Joseph Edward
Inverted troughs (ITs) over the Gulf of Maine are cool season phenomena that are responsible for unexpected high-intensity snowfall over coastal New England. An IT is a north and westward extension of relatively low atmospheric pressure that contains an easterly component of wind and cyclonic relative vorticity. These ITs have the ability to focus moisture into a low-tropospheric convergence zone, lift the air parcel into an unstable atmosphere, and produce high-intensity banded precipitation over a given region. This study creates an inceptive 25-year cool season (September-May) climatology of ITs over the Gulf of Maine from 1989 to 2013. The dynamical characteristics of the high intensity IT-influenced precipitation events are investigated via composite analyses that compare National Weather Service headlined and non-headlined ITs over the Gulf of Maine. This thesis will describe and present the roles of both quasi-geostrophic processes and mesoscale characteristics that influence IT genesis and evolution via composite cross section analyses and a case study. Results suggest that (1) north and westward extensions of quasi-geostrophic forcing for upward vertical motion removed from the sea-level pressure minimum of a parent-low pressure system can result in the genesis of ITs, (2) IT axes contain similar characteristics to frontal boundaries, and (3) the moist air along and upstream of the IT axes has potential to become unstable and produce quasi-stationary convective precipitation bands over a given region. The strong latent and sensible heat fluxes over the Gulf of Maine and cooling temperatures aloft (approaching upper-tropospheric trough) result a conditionally/symmetrically unstable environment that, given low-tropospheric forcing (frontogenesis) and middle-tropospheric forcing for upward-vertical motion, lead to a banded convective response. Operational forecasting techniques based upon the results of this study are presented in order to improve the forecasts of IT-influenced precipitation.