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

9

3. GENERAL CLOUD CHARACTERISTICS OF SIERRA STORMS

~ Before discussing the specific results of satellite studies for

SCPP, a background study of the literature provided information on

~
,

what is known about Sierran storms to date. This will allow comparison

to conclusions based on the results of the present satellite studies to

be given at the end of this report.

A. Convective Cells and Bands

Bands of convection imbedded in the large scale cloud mass are a

common characteristic of California coastal storms during the winter

(Fig. 30). The onshore movement of these bands has been studied by

Elliott and Hovind (1964) and their characteristics of size, speed, etc.

determined through the analysis of precipitation gage records from a

~~

coastal network. They found the bands to be 40 to 80 km wide, 60 to

120 km apart. Convective cells composing the bands moved relative to

w.

the bands towards lower pressure. Bands appeared to be oriented along

the shear vector between the upper level of the convective region and

the next level above the convection, while moving in the direction of

the low level shear vector. Convective activity was related to in-

creased instability within the storm due to differential temperature

advection.

Radar has been used to track cloud bands from offshore into the

Sierra during the CENSARE (Central Sierra Research) project which ran

from 1968-1973 (Peace, 1975). One to six bands per group may occur,

two or three bands being most common. Bands of 10 to 40 km radar

width are spaced 40 to 200 km apart, with their observed length often

.

being limited by the range of the radar itself. During large slow-

Pi