Publication Number: CEC-500-2005-004
Publication Date: December 2004
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Executive Summary
No executive summary.
Abstract
"Pineapple-express" circulations yield warm-wet storms along the west coast of North America and are known for the floods that they can generate. This study analyzed daily water-vapor transport pathways from the NCEP Reanalysis to identify the occurrence of these circulations throughout the 52-year period from 1948 to 1999, independently of whether the days were actually warm or wet on the West Coast. This approach identified 206 days on which large-scale atmospheric circulations were symptomatic of the pineapple-express condition.
These days all occurred between October and April, most often in January and February. The water-vapor transports crossed the West Coast anywhere from 32°N to 52°N, with a modest maximum near 45°N. The circulations have been most pronounced during winters when the PDO is in its positive, El Niño-like phase with ENSO in neutral or near-neutral conditions.
The circulations yield storms over the West Coast states (and into Nevada and Idaho) and warm conditions over most of the western states. In the Sierra Nevada during winter, the storms average about twice as much precipitation as other, non-pineapple-express storms, yield warmer minimum temperatures, and produce daily increases in streamflow that are an order of magnitude larger than those from other types of storms.
Table of Contents
No table of contents.