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THE WEATHER AND CIRCULATION OF MAY 1954

A Circulation Reversal Effected by a Retrogressive Anticyclone During an Index Cycle

WILLIAM H. KLEIN

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WILLIAM H. KLEIN

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WILLIAM H. KLEIN

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William H. Klein

Abstract

An objective method of forecasting surface temperature at 39 cities in the United States for 1, 2 and 3 days in advance has been developed and tested under operational conditions. This method utilizes daily input to multiple regression equations derived previously for predicting 5-day mean temperature from fields of 700-mb height and surface temperature. Comparative verification shows that the objective method produces forecasts which approximate the skill of subjective predictions made by experienced meteorologists.

Recent experiments are described which indicate that improved forecasts result when 700–1000 mb thickness is included as a predictor. The beneficial synoptic climatology which accrues from these studies is also illustrated.

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THE WEATHER AND CIRCULATION OF MARCH 1953 —

Including a Review of This Year's Mild Winter

WILLIAM H. KLEIN

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William H. Klein

Abstract

Multiple regression equations relating surface temperature to the mid-tropospheric circulation pattern are tested on observed 30-day mean 700-mb heights. The equations are found to specify monthly mean temperatures within one class out of five about 90 per cent of the time. This is better than results obtained by use of 5-day mean data from which the equations were originally derived.

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William H. Klein

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The “perfect prog” method of combining numerical and statistical weather prediction is applied to develop an automated system for forecasting the probability of precipitation at 108 cities on the mainland of the United States during daytime and nighttime periods from 12–60 hr in advance. Multiple regression equations are derived from a 4–5 year sample of data by seasons for each city by screening twice-daily geographical arrays of the following predictors: initial 850-mb height, initial 850–700 mb mean dew-point spread, and previous 12-hr precipitation at the network of surface stations. Each of the three predictor fields contributes about equally toward explaining the variance of the observed precipitation, but considerable geographical variation is exhibited by the equations. The forecast system is applied in an iterative fashion in 12-hr time steps by using as input numerical predictions of height and moisture at standard grid points as well as prior values of precipitation. The resulting computerized forecasts of precipitation probability, when applied on an operational basis in real time, may offer valuable guidance to the local weather forecaster.

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THE WEATHER AND CIRCULATION OF FEBRUARY 1955

ANOTHER FEBRUARY WITH TWO CONTRASTING REGIMES

WILLIAM H. KLEIN

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WILLIAM H. KLEIN

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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WILLIAM H. KLEIN

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No Abstract Available.

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