The purpose of this paper is to outline the development and use of a method for forecasting the time of formation of summer stratus clouds with ceiling of 2000 feet or less at Oakland Airport (California) between the hours of 4:30 p.m. and 6:30 a.m. In the development of this method special consideration has been given to the need for a procedure which can be used by forecasters who are new to the area under consideration and can benefit by a formula for forecasting the summer stratus, thereby eliminating the personal equation until such time as their experience in this area will justify the introduction of variations based on personal observations and studies.
In order to establish a meteorological forecasting system, it is necessary to find a direct relationship between measurable physical states of the atmosphere and the end product, the weather element to be forecast. The long range forecaster is quite limited in his choice of physical parameters. In fact only the very large-scale dynamics of the atmosphere which can be expressed in terms of mean pressure patterns are amenable to long range analysis. Thus the problem reduces to finding a link between mean planetary pressure patterns and precipitation in the Hawaiian Islands.
The investigation to be described in full in this report was started as a pilot project in July 1946, in an effort to improve and render more objective the precipitation anomaly estimates based on prognostic circulation patterns. Precipitation rather than temperature was investigated, because the forecast verification scores had been consistently lower on precipitation than on temperature forecasts.
The second phase of the Cloud Physics Project was carried on in the vicinity of Wilmington, Ohio, during the spring and summer of 1948. The organization, facilities, and general mode of attack were the same as those used in the first phase of the project. In this second phase of the study, the basic objective was to determine in definite quantitative terms the practical limits and economic importance of cloud modification processes in producing precipitation from cumuliform clouds.
"The primary purpose of this paper is to present a significant scale of meteorological events. This scale, the mesoscale, is either overlooked or intentionally ignored in much of the analysis being done today. The reason normally given for this omission is the fact that these meteorological motions are essentially 'noise' superimposed on larger-scale circulations and it is with these larger-scale circulations that most of the meteorologists' efforts (both theoretical and synoptic) have been concemed. It is our opinion, however, that this 'noise' is directly tied up with the local weather and that the meteorologist will have to despair of ever being able to predict this local weather with a satisfactory degree of confidence unless he has accurnte knowledge of what is going on in the mesometeorological scale of motion. In addition to focussing the readers attention on this scale of motion, it is also the purpose of this paper to serve as a preliminary manual for mesoanalysis. Although most of the analysis techniques have been given elsewhere (T. Fujita, 'Results of Detailed Synoptic Studies of Squall Lines', Tellus, vol. 7, No. 4, 1955, pp. 405-436), they are described fully here for completeness. Moreover, all of the ditta used in the analysis have also been reproduced in the form of station time sections. It is intended that these will serve two purposes: (1) The reader is encouraged to follow the techniques presented, perform his own mesoanalyses and compare them with the results given here, and (2) the reader will be able to interpret the sequence of events as they transpired at any station in terms of the mesosystems, developed in the analysis, which passed the station. Finally, we wish to point out that we have concerned ourselves here with analysis and not with explanation. The analyses clearly show the formation, development, movement, and dissipat ion of mesostruct ures. From this point of view the primary purpose of the paper is realized. However, there still remains the problem of explaining the life history of the mesostrnctures from a dynamical point of view"--Preface
By careful consideration of the observed winds and with the aid of various empirical and dynamics relationships, a steady-state 3-dimensional wind flow is deduced over northern California for a 24-hour stormy period. The production (or evaporation) of precipitation elements is estimated for all parts of the flow, the surviving elements are followed down to the surface, and the resulting precipitation with the observed.
The basic objective of this Project was to determine in definite quantitative terms the practical limits and general utility of cloud modification processes in producing or suppressing precipitation and increasing the visibility from flying aircraft. In order that the effects of the induced modifications may be clearly separated from those occurring naturally, a closely coordinated attack using all available measuring facilities was adopted.
The estimation of the volume of runoff to be expected from a given volume of rainfall is a fundamental problem in flood forecasting. Such estimates are necessary before the unit hydrograph or other techniques can be used to predict the streamflow hydrograph. The authors describe the technique now used at the River Forecast Centers of the U.S. Weather Bureau for evaluating the effect of season, antecedent conditions, duration of rainfall and rainfall amount in determining the portion of the rainfall contributing to storm runoff. Special problems encountered in flood forecasting are emphasized. The technique, developed and tested over several years, yields a high degree of accuracy in estimated runoff. Although prepared by empirical procedures, the close agreement between relations for basins of similar hydrologic characteristics suggests that rational parameter have been adopted. The similarity between relations also simplifies the work required for their preparation.
In the summary, suggestions are made relative to the inclusive of the theory discussed in this paper in the day-to-day analysis of the weather. Indications are also given for the extension of the hydraulic analogy beyond the point covered in this paper.
