SPECIFICATION OF PRECIPITATION FROM THE 700-MILLIBAR CIRCULATION

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  • 1 Extended Forecast Branch, National Meteorological Center, U.S. Weather Bureau, Suitland, Md. 1
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Abstract

Five-day precipitation amounts observed during 10 recent winters in 40 equal-area circles covering the United States are assigned a numerical index according to the proportion of light, moderate, or heavy precipitation falling within each circle. The synoptic climatology of precipitation is investigated through construction of correlation fields between this index and the simultaneous 5-day mean 700-mb. height departure from normal in North America and adjacent ocean areas. On the basis of the analogy between lines of equal correlation and lines of equal height anomaly, inferences are drawn concerning the association between precipitation and other meteorological factors. Schematic models are then constructed showing preferred portions of the long-wave pattern for heavy and light precipitation in different parts of the nation.

By use of a screening program on the IBM 7090, the field of 700-mb. height is found to be more effective than that of either sea level pressure or 700–1000-mb. thickness in specifying 5-day precipitation. On the average, almost 40 percent of the variance of precipitation can be explained by 2 to 6 heights, but the specification is more accurate in the West and South than in the East or North. Multiple regression equations are derived for each reference circle and found to hold up well on 4 years of independent data.

Abstract

Five-day precipitation amounts observed during 10 recent winters in 40 equal-area circles covering the United States are assigned a numerical index according to the proportion of light, moderate, or heavy precipitation falling within each circle. The synoptic climatology of precipitation is investigated through construction of correlation fields between this index and the simultaneous 5-day mean 700-mb. height departure from normal in North America and adjacent ocean areas. On the basis of the analogy between lines of equal correlation and lines of equal height anomaly, inferences are drawn concerning the association between precipitation and other meteorological factors. Schematic models are then constructed showing preferred portions of the long-wave pattern for heavy and light precipitation in different parts of the nation.

By use of a screening program on the IBM 7090, the field of 700-mb. height is found to be more effective than that of either sea level pressure or 700–1000-mb. thickness in specifying 5-day precipitation. On the average, almost 40 percent of the variance of precipitation can be explained by 2 to 6 heights, but the specification is more accurate in the West and South than in the East or North. Multiple regression equations are derived for each reference circle and found to hold up well on 4 years of independent data.

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