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<br />Moisture that exists in the atmosphere at the start or during a <br />storm can be measured by integrating the specific humidity measured in <br />radiosonde observations at locations in the storm area. Total moisture <br />in the atmosphere above the earth's surface can then be expressed in <br />.illimeters as a depth. Amounts vary greatly. but the general arder of <br />magnitude is about 50 millimeters. Maximum moisture that can occur <br />during a storm is usually considered to be that which would correspond <br />to saturated air at temperatures that would correspond to a pseudo- <br />adiabatic lapse rate curve "ssing through the pressure and temperature <br />point at the source of moisture. Since the source of moisture is <br />usually an ocean surface. the Maximum ocean-surface water temperature <br />at the time of year would be used as the maximum surface temperature <br />(and dew point). Curves of teMperature and moisture vs. surface teM- <br />perature for pseudo-adiabatic lapse rates are given in figures 4.01 and <br />4.02. <br />It is usual practice to assume that storm precipitation for the <br />same storm Mechanis. would be proportional to the precipitable water. <br />Thus, insofar as the influence of moisture in the airmass is concerned. <br />recorded storm precipitation can be maximized by multiplying by the <br />ratio of maximum probable precipitable water to recorded storm preci- <br />pitable water. <br />The factor of storm IeChanism is more difficult to ..asure and <br />assess in relation to the effect on storm precipitation. In convective <br />type storms. it is usually assumed that such large nuMbers of these <br />storms occur that a near-maximum mechanism occurs someplace in the <br />region during a long period of observation. Thus a simple envelope of <br />rainfall amounts adjusted for maximum moisture might well represent <br />probable maximum convective-storm precipitation. In the case of cy- <br />clonic storms. wind velocity is a good index of storm-mechanism inten- <br />sity. Maximum probable winds can be estimated by an envelope procedure <br />using observed winds in a large number of cyclonic storms. Some mod- <br /> <br />4-02 <br />