WMOD00579

• Title: An Exploratory Forecast Experiment to Predict Supercooled Liquid Water in the Sierra Nevada
• Date: 11/1/1988
• Weather Modification - Doc Type: Report

1.0 INTRODUCTION

The Sierra Cooperative Pilot Project (SCPP) was a ten year
wintertime cloud modification research program sponsored by the
Bureau of Reclamation to determine the potential for increasing
the sno~~ack, through application of cloud seeding, in the
&~erica~ River Basin (see Fig. 1). An overview of the SCPP
program and the design of two separate randomized exploratory
cloud seeding experiments have been presented by Reynolds and
Dennis (1986). The second of these two experiments, called the
Fixed Target Experiment, focused on the shallow widespread cold
orographic cloud as providing the best opportunity for increasing
precipitation through glaciogenic seeding. These cloud types
provided the longest lasting episodes of supercooled liquid
water (SLW) as determined by a dual-channel microwave radiometer
operating near the crest of the Sierra Nevada (Heggli and
Rauber, 1988).

The shallow cold orographic clouds often appeared following
the passage of a split-front or kata cold front (Heggli and
Reynolds, 1985, and Reynolds and Kuciauskas, 1988). This
preli~inary finding provided project forecasters with some clues
on which to base their forecast of conditions suitable for
seeding activities. Therefore during the last two field seasons
of SCPP (i.e., 1985-86 and 1986-87), an exploratory forecast
experiment was undertaken to examine how well the timing of
frontal passage could be translated into forecasting the onset,
duration, and concentration 0= SLW over the Sierra Nevada.

It should be noted that the forecasting for a research field
prograE is differe~t than standard weather forecasting by the
National Weather Service. The environment, the type of forecast,
a~d the available data sets can be quite different. Typically
t~e field research program first utilizes a planning or outlook

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