Document Type

Article

Publication/Presentation Date

11-2005

Abstract/Description

This study compiles and interprets three-dimensional Weather Surveillance Radar-1988 Doppler (WSR-88D) data during a 2.5-yr period and examines the typical orographic effects on precipitation mainly associated with winter storms passing over coastal northern California.The three-dimensional mean reflectivity patterns show echo structure that was generally stratiform from over the ocean to inland over the mountains. The flow above the 1-km level was strong enough to be unblocked by the terrain, and the mean echo pattern over land had certain characteristics normally associated with an unblocked cross-barrier flow, both on the broad scale of the windward slopes of the coastal mountains and on the scale of individual peaks of the terrain on the windward side. Upward-sloping echo contours on the scale of the overall region of coastal mountains indicated broadscale upslope orographic enhancement. On a smaller scale, the mean stratiform echo pattern over the mountains contained a strong embedded core of maximum reflectivity over the first major peak of terrain encountered by the unblocked flow and a secondary echo core over the second major rise of the coastal mountain terrain.Offshore, upstream of the coastal mountains, the reflectivity pattern showed a region of enhanced mainly stratiform echo within ∼100 km of the coast, with an embedded echo core, similar to those over the inland mountain peaks, along its leading edge. It is suggested that the offshore enhancement is caused by intensified frontogenesis in the offshore coastal zone and/or by the onshore directed low-level flow rising over a thin layer of cool, stable air dammed against the coastal mountains.The orographically enhanced precipitation offshore and over the coastal mountains was present to some degree in all the landfalling storms. However, the degree to which each feature was present varied. All the features were more pronounced when the 500–700-hPa flow was strong, the midlevel humidity was high, and the low-level cross-barrier wind component was strong. When the low-level stability was greater, the offshore enhancement of precipitation was proportionately increased, and the general broadscale enhancement inland was reduced.

Publication Title

Monthly Weather Review

Required Publisher’s Statement

© Copyright 2005 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org.

Download

Included in

Meteorology Commons

Share

COinS