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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moving storms, two to three groups of bands may occur 12 to 24 hours

apart. A cold front often follows the last band of each group.

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The bands observed by radar are oriented north to south or north-

east to southwest and are well organized offshore. In crossing the

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Coast Range they become somewhat disorganized, and reorganize upon

reaching the Central Valley. Upon encountering the Sierra foothills,

the northern end of the band slows until the band becomes parallel to

the Sierra Nevada, oriented north-northwest to south-southeast. This

is because individual cells in the line begin to curve cyclonically at

the foothills until they are moving roughly parallel to the barrier.

At this time, line echoes tend to break up into individual cells that

climb the slope.

In the vertical, convective cells tend to be imbedded and extend

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upward out of a more shallow layer. At low scan angles, the cells are

indistinguishable from the shallow layer at full radar gain. During

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CENSARE vertically-pointing radar showed no evidence of a layered

structure in the detectable cloud, with only one exception where two

layers were detected. Higher tops were found in warmer storms with

higher precipitation rates. Finally, Peace found that echo movement

was close to the 2500 to 3000 m winds aloft, and both showed cyclonic

curvature nearing the Sierra crest.

Observations of mesoscale convective bands are not limited to

California coastal storms. A very detailed study has been made of a

continental occlusion in New England (Kreitzberg and Brown, 1970).

Convective bands associated with both the warm and cold fronts con-

tained cells which accounted for most of the precipitation in the

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system. In their study, warm frontal bands were atrributed to tongues

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