WMOD00548

• Contract/Permit #: 6-07-DR-20020
• Project Name: Sierra Cooperative Pilot Project
• Title: Satelite Studies During the 1976-77, 1977-78 Sierra Cooperative Pilot Project
• Date: 2/1/1979
• Weather Modification - Doc Type: Report

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of warm moist air, over the frontal surface aloft, being overrun by

cooler air and breaking out into convective bands within the stratus

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deck. Ahead of the cold front, bands were associated with a prefrontal

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surge of cold air and behind it, with the cold front itself. Again,

the bands were oriented along the shear vector as in the Pacific Coast

storms above. This orientation also parallels the surface front with

which the bands were associated.

Additional studies by Matejka et al. and Hobbs et al. (both 1978)

confirmed the results of Kreitzberg and Brown while also relating the

mesoscale features to cloud microphysics and precipitation efficiency.

One result of Hobbs et al. which differs from those of Elliott and Hovind,

and Kreitzberg and Brown, is in the speed and direction of motion of

prefrontal bands and cells. Hobbs et al. found the motion to be similar

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to, not to the right of, the winds between 3 and 6 km, near the upper

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level of the convection. Their aircraft flights show that large amounts

of supercooled water exist within the cells, an important finding for

weather modification purposes.

B. Sierra Orographic Clouds

Rainfall records within the Sierra range point to the orographic

enhancement of precipitation on the upwind side of the barrier (Lamb

et al., 1976). While the effect on precipitation may be the same as for

inland mountains such as the Rockies, it has long been realized that

the winter orographic clouds for the two are very different. The

average Sierra storm is much wetter and warmer than continental storms,

due to the proximity of the Pacific Ocean, the onshore flow during storm

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events, and the relatively low elevation of the upwind Central Valley.

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