Some aspects of post-frontal convective areas along the West Coast of the United States

Description

The European Center for medium-Range WEather Forecasts (ECMWF) Level III-b analyses are used to study cases of post-frontal convective areas that occurred off the West Coast of the United States. A five-year climatology suggests than an average of about 13 convective events occurs each winter, and that two of three cases are likely to have intense and well-organized convection. Five events that occurred during the First Special Observing Period of the First GARP Global Experiment are selected for detailed study, Associations are sought between the post-frontal convective areas and standard synoptic and dynamic variables. The convection appears to be closely tied to the position of the upper level cold trough. Cold advection aloft and low-level heating as the cold air streams over the warmer ocean contribute to maintenance of low static stability in the convective region. The feasibility of diagnosing the location of the convective regions is explored with diabatic and frictional parameterizations of the Naval Operational Global Atmospheric Prediction System (NOGAPS). Wind, temperature, geopotential and moisture fields from the ECMWF are used to specify the large-scale forcing. The cumulus precipitation diagnosed by the NOGAPS does agree surprisingly well with the post-frontal convective areas in these five cases. (Author)

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