WMOD00310 ‎(2)‎

• Project Name: Sierra Cooperative Pilot Project
• Title: The Characteristics of Evolution of Supercooled Water in Wintertime Storms Over the Sierra Nevada
• Date: 9/9/1988
• Weather Modification - Doc Type: Report

998

JOURNAL OF APPLIED METEOROLOGY

VOLUME 27

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fiG. 6. Supercooled liquid water depth (mm) measured vertically by the radiometer between 0900 UTC 26
March 1985 and 0900 UTC 28 March 1985 at Kingvale. The precipitation rate at Kingvale is also shown.

seeder-feeder precipitation mechanism (Matejka et al.
1980). A deeper moist layer continued to affect the
region through 0900 28 March, when measurements
were terminated.
Discussion. The 26-29 March 1985 storm was one
of 14 storm systems that developed in strong westerly
or southwesterly flow during the four field seasons.
These storm systems consistently produced sustained
high precipitation rates and the largest precipitation
amounts in the Sierra Nevada. The storms all had long
(~45 h or greater) durations. The synoptic-scale evo-
lutions were generally similar to that described for the
26-29 March case. A warm front was typically observed
at the leading region of the storms. Strong cold fronts
were present. In certain storms, the jet stream axis was
near the position of the surface front. In other cases,

the jet stream axis led the surface cold front and the
subsidence region evident in Fig. 5 was displaced over,
rather than behind, the cold frontal position. An oro-
graphic cloud, usually with embedded convection, re-
mained after frontal passage. In some cases, such as
26-29 March, secondary moisture regions advected
into the area, enhancing precipitation rates. These re-
gions were associated with weak, secondary waves de-
veloping within the storm. Weak convective instability
generally was present throughout the postfrontal pe-
riod.
Because of the orientation of flow fields in these
storms, the majority were characterized by high freezing
levels in central California. As a result, rain often fell
at the radiometer site, and radiometric data in these
cases were contaminated by the rainfall. Of the 14