A Case for Detailed Surface Analysis

Abstract

Detailed analysis of the temperature and moisture fields based on routine hourly surface observations in North America can provide a rational basis for surface feature analysis, thus clarifying the present confusion. Recognition of surface features is an important part of weather forecasting and is especially needed in a careful diagnosis for the prospects of deep convection. Surface temperature gradients are advocated as the primary basis for identifying fronts; examples are given of gross discrepancies in current operational practice between the surface temperature fields and the associated frontal analyses. Surface potential temperature, selected as a means of compensating for elevation differences, is analyzed in the western United States for a period in which a strong, damaging cold front develops and dissipates over a period of less than 24 h. Frontogenesis-related calculations, based on detailed surface temperature analyses, help to explain a case of focusing of heavy precipitation in northern Kentucky that produced a flash flood. Conditions for the initiation of intense convection are illustrated by detailed analyses of the surface moisture and temperature fields. These are used to estimate the buoyancy of surface air lifted to midtroposphere and show the relationship of this buoyancy to ensuing convection. The analyses aid in recognition of the surface dryline (a feature commonly misanalyzed as a cold front) and those convectively produced pools of cold air at the surface that often play a major role in the subsequent redevelopment of convection. The proposed analyses might be difficult to achieve manually in operational practice during busy weather situations, but this could be facilitated by using objective methods with present and prospective workstations. Once surface features are identified, their temporal and spatial evolution must be followed carefully since they can change rapidly.