Winter orographic precipitation ratios in the Sierra Nevada: Large-scale atmospheric circulations and hydrologic consequences

Journal of Hydrometeorology
By: , and 

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Abstract

The extent to which winter precipitation is orographically enhanced within the Sierra Nevada of California varies from storm to storm, and season to season, from occasions when precipitation rates at low and high altitudes are almost the same to instances when precipitation rates at middle elevations (considered here) can be as much as 30 times more than at the base of the range. Analyses of large-scale conditions associated with orographic precipitation variations during storms and seasons from 1954 to 1999 show that strongly orographic storms most commonly have winds that transport water vapor across the range from a more nearly westerly direction than during less orographic storms and than during the largest overall storms, and generally the strongly orographic storms are less convectively stable. Strongly orographic conditions often follow heavy precipitation events because both of these wind conditions are present in midlatitude cyclones that form the cores of many Sierra Nevada storms. Storms during La Niña winters tend to yield larger orographic ratios (ORs) than do those during El Niños. A simple experiment with a model of streamflows from a river basin draining the central Sierra Nevada indicates that, for a fixed overall basin-precipitation amount, a decrease in OR contributes to larger winter flood peaks and smaller springtime flows, and thus to an overall hastening of the runoff season.


Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Winter orographic precipitation ratios in the Sierra Nevada: Large-scale atmospheric circulations and hydrologic consequences
Series title Journal of Hydrometeorology
DOI 10.1175/JHM-390.1
Volume 5
Issue 6
Year Published 2004
Language English
Publisher AMS
Contributing office(s) Toxic Substances Hydrology Program, San Francisco Bay-Delta, Pacific Regional Director's Office
Description 15 p.
First page 1102
Last page 1116
Country United States
Other Geospatial Sierra Nevada
Online Only (Y/N) N
Additional Online Files (Y/N) N