Frequent rainfall during the winter months in the Portland, Oregon region is associated with extratropical cyclones modified by the Coastal and Cascade Ranges. Operational WSR-88D radar observations from Portland, OR and upper-air soundings from Salem, OR over a 3-year period (2003-2006) from 1 November ? 31 March are used to determine a 3D climatology of winter storms. 84 % of the 117 storm events had a low-level wind direction from the south or southwest, between 158° - 248° azimuth. Stability varied between storms, with most storms being neutral to slightly stable. Wind direction was found to be more important in determining the geographic pattern of precipitation in the PNW. For S-SW flow storms, increasing the storm volume is primarily related to increasing precipitation frequency rather than precipitation areal coverage. Local maximum in precipitation frequency is seen typically at mid-windward slope rather than at the Cascade Range crest. 3D radar observations were also compared to MM5 output for the 2005-06 and 2006-07 winter seasons. Storms were grouped by their prevailing low-level wind direction and two individual cases (2005 Dec 29-31; 2006 Nov 6-7) to compare their radial velocity, precipitation frequency, and standard deviation of radial velocity. Errors were found in the standard deviation of Vr, with the model showing more variable wind speed and direction than the observations. The spatial pattern of precipitation frequency between the radar observations and model output were found to be similar, but the magnitudes were found to usually be larger in the model output.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-08302007-145441 |
| Date | 01 October 2007 |
| Creators | Payne, Matthew J |
| Contributors | Sankar Arumugam, Sandra Yuter, William Showers |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-08302007-145441/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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