| OCR Text |
Show In Figure 141, wind dire ction sh ea r with height spread the expected see d t~d precipitation over a wide area. The transport time to fallout location was only 20-30 minutes from aircraft release time . Percentage contours of 3hour seeded precipitation period to total 6-hour precipitation do seem to maximiz e near the c e nter of the projected seeded area and near th e -1 OC crystal fallout line. These percentage contours were drawn from weighing bucket ,data, supplemented at a few stations by light sensor data (ligh_t sensor values are encircled). Maximum aircraft seeding effects should have been observed betwe e n 1630 and 1730 MST. This prediction is compared to observed radar and we i ghing bucket data in the next section. 4. 5. 4. 1. 7 Weighing Bucket and Lodwick Vertical Pointing Radar AGC Records According to the trajectory calculations in Section 4. 5. 4. 1. 6, se e ding e ffects should have been at a maximum over the Lodwick vertical pointing radar from 0810 to 0910 MST from ground seeding, and from 1630 to 1 730 MST from aircraft seeding. A study of Figures 143-145 indicates a secondary maximum in AGC voltage values from 0825 MST to 0908 MST and from 1636 MST to 1748 MST. Thus, the agreement in time is quite good in these two c ases. In order to compare recorded precipitation values to the predicted seeding effects, hourly weighing bucket totals were graphed for e ach available station for the entire calendar day of 16 November 1968. These histo gr ams are shown in Figures 146 -15 5. A study of these graphs, with reference to predicted seeding effec t tim e, shows general good agreement for the morning ground se e din g, especially co nsid e ring the minimum time increment of one hour for weighing bucket totals. A definite precipitation rate increas e can be tracked southward with time across the ex perimental area, in general accord with predicted seeded precipitation. However, it lasts into early aft e rnoon over the southern edge of th e area. Whether or not this was lingering seeding effect is discussed in th e following se_c tion_s . The fact that Mt. Harris also experienced a maximum in hourly precipitation totals from 07-0800 and 08-0900 MST led to the suspicion of an east - west oriented snow band drifting s lowly southward across the ar e a. Evidence of this band will be shown from PPI photos. No noticeable increase in precipitation rates was evid e nt between 1600 and 1700 MST in the weighing bucket records, except at Long Lake. Base Camp increased in rate betwe e n 1 700 and 1800 MST, but no conclusions regarding aircraft seeding effect ar e possible. 229 |
