OCR Text |
Show 4. 5. 3. 2. 1 Synoptic Pattern, Moisture, and Stability Moist air was flowing in a general west-northwest current aloft. There were no identifiable fronts moving across the area, but a very weak short wave was evident on the 700 mb map (Figure 122). This produced veering of winds aloft during the operation (Figure 12 3). Precipitating orographic cloud tops were quite obviously no higher than 16, 500 ft. MSL (525 mb and -23°C temperature) at 1935 MST (Figure 124) and 15, 000 ft. MSL (555 mb and -22°C temperature) at 22 50 MST (Figure 125). Unstable stratification prevailed from the surface to 620 mb (12, 700 ft. MSL) at 1935 MST. On the 2250 MST sounding (Figure 125), taken during the seeded three hour period, a surface-based inversion prevailed to 735 mb (8400 ft. MSL) with unstable stratification above to 580 mb (14, 000 ft. MSL). This su.r face inversion very likely tra1Jped the seeding material with no significant vertical diffusion through the inversion into the precipitating cloud layer. 4. 5. 3. 2. 2 Seeding Schedule Silver iodide was released at Mt. Harris from 2100 to 2200 MST. 4. 5. 3. 2. 3 Computed Seeded Precipitation Fallout Area Making the assumption that the seeding material was able to diffuse upward through the existing inversion, the seeded precipitation fallout area shown in Figure 126 was computed. Earliest arrival time of seeding effect at Rabbit Ears Pass was computed to be 2300 MST. 4. 5. 3. 2. 4 Precipitation Rate Character Figure 127 shows the optical snow-rate sensor records for Rabbit Ears Pass and Buffalo Pass, with the computed three-hour seeding effect period for Rabbit Ears. No seeding effect is evident on these traces. 4. 5. 3. 2. 5 Silver-in-Precipitation (AAS Values) Snow samples from Rabbit Ears analyzed for silver content (Table 15) showed no significant amount of silver during any of this operation period. This lends support to the hypoth~sis that seeding material remained trapped be neath the inversion. 4. 5. 3. 2. 6 Crystal Types and Riming Dendrites occurred throughout the period, while plates were observed only during the unseeded period. Riming rates at Rabbit Ears increased during 201 |