Laserfiche WebLink
<br />003477 <br /> <br />closest to this average. * We assumed that this sounding represented all <br />air about to enter the state. One sounding may not be able to do this, <br />of course, but this is the only practicable way to work with these <br />sounding data. <br /> <br />Next, the selected sounding was examined for sufficient moisture to <br />produce clouds when the incoming air was lifted orographically. A <br />sounding was assumed to identify a storm if its relative humidity at 600, <br />650 and 700 rob averaged at least 65 percent. Sixty-five percent was <br />chosen because air at 700 rob at a typical temperature of -10 degrees <br />Centigrade and 65 percent relative humidity reaches saturation when it is <br />forced to rise 60 mb--the amount of vertical motion that typically occurs <br />as air crosses the Colorado mountains. The 600-700 rob layer was selected <br />to ensure development of a low-level cloud at least one kilometer thick. <br /> <br />This method of identifying storms has several limitations. First, <br />intensity or duration of the storms cannot be determined. Second, <br />rapidly moving storms may pass by undetected between sounding times. <br />Third, it may snow even though the storm criteria have not been met, or <br />it may not snow when the criteria have been met. <br /> <br />The number of storms identified each winter in each sub-region are <br />shown in Figures 3 through 7. The number of storms varied markedly <br />during the 13 winters--from 88 in 1962-63 to 168 in 1964-65. In general, <br />the number appears to increase with the wetness of the winter. There <br />were many exceptions, however 1 the most dramatic of which occurred in <br />1973-74 in the north Sub-region. This was the wettest winter in the <br />north (in terms of snowcourse water content), but fewer storms (104) were <br />identified than in all but one of the other drier winters. <br /> <br />*Millibars are used by meteorologists as a unit of atmospheric pressure. <br />Pressure decreases with height. Seven hundred rob is approximately 10,000 <br />feet, while 600 rob is about 14,000 feet. <br /> <br />18 <br />