On the Late Frost Forecasting in Matsumoto Basin, Nagano Pref.

Abstract

1. The late frost damage in this area begins usually from the middle of the last decade of April and threatens all through May. But, in the spring when the weather advances, it sometimes occurs earlier. Therefore, it is insufficient to learn only the perilous period in calendar, but is necessary to duly deliberate the frost-tolerance of crops variable at each stage of their growth. The writers accordingly accumulate the temperatures over 3°C of the daily mean air temperatures from Jan. to the previous day in considerationthe so-called accumulative temperaturein order to get anindex which indicates the growth stage of the crops. As far as this area is concerned, we found that it is the begining of the perilous period of frost damage when the index becomes 150°C.2. We next studied statistically on the relation between the existence of frost its predictor based on the date obtained these 44 years.Using these results, we may forecast the forming of frost with the following measures.Step 1. —First of all, decide whether the prognostic pressure pattern is of frosty type or not as is shown in Fig. 2.Step 2. —In the case of the late frosty pressure pattern, read the air temperature and the vapour tension at 6 P. M. In TE diagram (i.e. Fig. 3), take P whose coordinates are these readings in order to decide section in which P is located.(a). When P is in Section A, the succeeding morning is frosty in 92-100% probability. (b) When P is in Section D, the succeeding morning is free from frost in 98-100% probability. (c). When P is either in Section B or C, one has, furthermore, to rely upon the following means.Step 3.—(a). When the weather is clear or fine at 6 P. M. and the weather is forecasted to be clear till the succeeding dawn, it forms in 76-94% probability if P is in Section B, and in 31-66% probability if P is in Section C. (b). In the case of the weather different from the above mensioned conditions: —In order to have frost in the succeeding dawn, we have upper limits of air temperature at 6 P. M. for each weather condition shown in Table 3. Under these conditions, the frost is expected with in the confidence limits of occurrence probability indicated in the last column of the table.3. When the frost is expected with the above mentioned measures, we can estimate the frost intensity by the following means.Step 1—(a) When P is in Section C at T-E diagram, the expected frost in the successive dawn is weak in 72-100% probability. (b). When P is either in Section A or B in the figure, it has to be forecasted according to the following measures.Step 2— From the weather conditions at 6 P. M. and the successive prognostic weather, the frost is judged to be strong within the confidence limits in the last column of Table 5 in accodance with the weather conditions of the table.