WMOD00317 (2) - Laserfiche WebLink

Home Browse Search

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