Chapter 8 

 METEOROLOGY— FORECASTING 



8 1 FORECASTING TEMPERATURE AND 

 MOISTURE DISTRIBUTION OVER 

 MASSACHUSETTS BAY" 



BEFORE GOING into a description of the forecast 

 Ijrogram and results it will be profitable to describe 

 the method used in coordinating the observations. 



8.1.1 Meteorological Observations 



Soundings were made according to two major 

 plans. The first was in conjunction with the radio 

 path. According to that plan, airplane soundings were 

 made once or twice a day at two or three points along 

 the transmission path. The boat would take either 

 mast or balloon soundings along the path while meas- 

 urements at Race Point Light (Provincetown) would 

 continue at 2- to 4-liour intervals during most of the 

 day and sometimes at night. The Race Point Station 

 had the advantage of being well away from land (for 

 all but easterly winds) and soundings there would 

 thus represent the condition of the air over a large 

 portion of the path. The soundings just described 

 were made primarily for correlation with the signal 

 strength measurements. 



The second plan was to obtain soundings in succes- 

 sive steps in air moving oft' the coast as that air be- 

 came more and more modified by the cool ocean sur- 

 face. For this reason, days during which the air was 

 westerly or nearly so were set aside for this type of 

 measurement. The Duxbury soundings gave a rep- 

 resentation of the structure of the air before it left 

 the land. One airplane made soundings at about 2, 

 7, and 25 miles offshore. The times of take-off were 

 staggered to allow the first airplane to complete its 

 third ascent before the second plane would begin its 

 first sounding. 



The boat played a vital role in such a plan. It ran 

 along the line of the air trajectory for as long as was 

 practicable to take water temperature measurements 

 and mast soundings, usirally an 8- to 10-hour period. 



The Race Point Meteorological Station was coor- 

 dinated into this general plan by having it take con- 

 tinual balloon soundings at, say, 2-hour intervals 



"By I. Katz, Radiation Laboratory, Lt. J. R. Gerhardt, 

 Lt. W. E. Gordon, Army Air Forces, and P. W. Kenworthy, 

 U. S. Weather Bureau, Boston, Mass. 



both before and after the airplane ascents. The pur- 

 pose of these soundings was both to fit in as an extra 

 sounding in the general plan and also to yield some 

 information as to amounts of change of the meteoro- 

 logical conditions with time. Also, in general, the 

 times of soundings at Race Point Station were sched- 

 uled about 1 hour later than those at the overland 

 station to give the air sufficient time to travel from 

 one to the other. 



®'^'^ Forecast Program 



A forecast program was begun during July and 

 continued to October 10, ID 44, in order to try out 

 existing methods of forecasting and to help develop 

 new techniques. A more natural step would have been 

 to analyze the data taken during the summer and 

 then to put that analysis into the form of forecast 

 procedures, as was done at the end of the 1943 Boston 

 Harbor transmission exjDeriment. However, since speed 

 was essential it was decided to initiate a forecast pro- 

 gram simultaneous with the observations. The very 

 act of forecasting tended to focus attention on the 

 important weather factors, at the same time giving 

 invaluable help in planning the day-to-day observa- 

 tions. 



The typie of forecast made was different from the 

 usual form. It consisted of a "space forecast" rather 

 than the usual time forecast. That is, knowing the 

 conditions at one point at a given time the problem 

 was one of finding the conditions at another location 

 at the same time. It involves the entire problem of 

 modification of an air mass by a water surface. 



The forecasts were in the form of curves of tem- 

 perature and moisture, from which the modified in- 

 dex curve was computed. A time and a location in 

 Massachusetts Bay were selected at which it had been 

 determined previously that a sounding would be made. 

 Almost invariably airplane observations were choseii 

 to use as verifications because those soundings were 

 at sufficient altitudes so that both the modified and 

 the unmodified air were sampled. The forecasts were 

 made from the surface to 1,000 ft, whereas the air- 

 plane soundings started from about 20 ft and con- 

 tinued to 1,000 ft. For verification, the forecast and 

 the sounding were plotted on the same graph. 



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