Theme for 2002:
Understanding and Responding to California Precipitation Patterns

June 21, 2002
Sierra College, Rocklin, CA

Speaker Presentations

Reconstruction of 1000 Years of Runoff for the Sacramento River System Using Tree Rings

Maurice (Maury) Roos
Chief Hydrologist (part time)
Division of Flood Management
California Department of Water Resources
Sacramento, CA


[Abstract not available]

A Synoptic Climatology of Heavy Precipitation Events in California

Alan Haynes
Hydrometeorological Analysis and Support (HAS) Forecaster
California-Nevada River Forecast Center
National Weather Service
Sacramento, CA


Historical heavy precipitation events were defined for three different climatic regimes in California, including the south coast drainage basin, the north coast basin and the Sacramento basin. Synoptic patterns were associated with these events using gridded NMC analyses. The purpose of this study was to identify the primary large-scale features associated with heavy precipitation in the various climatic regimes of California and to document the synoptic climatology of these events.

For simplification, heavy precipitation events were defined for three classifications. The first classification was defined by at least 3 stations receiving .3.00 inches of liquid equivalent precipitation in one day. Thesecond class was defined by at least 3 stations receiving .6.00 inches in two consecutive days and the third class was thesame as class 2, but with the added stipulation that at least one station received .10.0 inches in two consecutive days.

Various synoptic patterns were identified and composited with each of these cases. There was a great deal of similarity between pattern types in the North Coast basin andthe Sacramento basin. Some of the main features which appeared to contribute to heavy rain included strong westerly flow across the Pacific Ocean into California or a large scale upper level trough or closed low off the Pacific Northwest/British Columbia coast into the Gulf of Alaska with southwesterly flow into California. Sometimes there was a blocking upper level high over the Pacific in the vicinity of Alaska and sometimes the upper jet was displacedequatorward, especially in the South Coast cases. A sea level low pressure area was generally present along the west coast of North America in the vicinity of the Pacific Northwest or British Columbia, with varying pressure gradient strength across California. The Sacramento basin had the most frequent occurrence of heavy rain as defined for this project, while the South Coast had the least frequent. The Sacramento basin had more cases that were difficult to classify than the other basins and also had some cases with weaker synoptic features that were evidently still able to produce heavy precipitation. Heavier precipitation events, defined as the second class, were associated with stronger synoptic features, such as lower heights, a stronger upper jet and deeper sea level pressure lows and a few events appeared to be mainly attributable to more tropical moisture. The stronger synoptic features usually provided stronger orographic ascent and sometimes allowed a tap into subtropical moisture. There were also some events where an injection of cold continental air into the upper trough appeared to compensate for less moisture.

Seasonal Predictability of Daily Precipitation: Frequency of Heavy Events

Alexander Gershunov, Ph.D.
Assistant Project Scientist
Climate Research Division
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, CA


This work explores statistical seasonal predictability of precipitation in the contiguous United States for all seasons. Although it is shown that total seasonal precipitation and frequencies of less-than-extreme daily precipitation events are more predictable, the focus is on frequency of daily precipitation above the seasonal 90th percentile (P90). Frequency of such heavy daily precipitation is shown to be predictable due to ENSO as well as to non-ENSO forcing at lead times of up to six months. Significant predictability achieved in the Northwest, Great Plains, and the eastern US is mostly ENSO-related. However, southwestern precipitation is predictable even in non-ENSO winters.

Improving Precipitation Forecasts in Land-falling Pacific Winter Storms: PACJET Results and Future Outlook

F. Martin (Marty) Ralph, Ph.D.
Regional Weather and Climate Applications Division
NOAA, Environmental Technology Laboratory
Boulder, CO


Section 1: Science results

  • The Statistical Relationship Between Upslope Flow and Rainfall in California's Coastal Mountains: Observations during CALJET
  • An Automated Brightband Height Detection Algorithm for Use with Doppler Radar Spectral Moments
  • Bulk Microphysical Characteristics of Rainfall Observed at a California Coastal Mountain Site During CALJET
  • The Impact of a Prominent Rain Shadow on Flooding in California's Santa Cruz Mountains: A CALJET Case Study and Sensitivity to the ENSO Cycle

Section 2: Programmatic Discussions

  • Overviews of the PACJET-2001 field study
  • Overviews of the PACJET-2002 field study
  • Summary of the planning meeting of October 2001

Using Historical Radar-Rainfall Data to Evaluate the Sizes, Shapes, Orientations, and Tracks of Storm Cells

David C. Curtis, Ph.D.
NEXRAIN Corporation
Orangevale, CA


A historical database of 2 km x 2 km 15-minute radar-rainfall estimates was used to study the sizes, shapes, orientations, and depth-area characteristics of storms in Clark County, NV and nearby regions of California, Arizona, and Utah. More than 100,000 individual 15-minute storms were evaluated over a four year period. The size, shape, orientation, track, and the three-dimensional characteristics of each storm were cataloged.

Forecast-Based Operations of the Yuba and Feather River System

Ben Tustison
Water Resources Engineer
MBK Engineers
Sacramento, CA


[Abstract not available]

Options for Forecast-based Operation of Folsom Reservoir

David S. Bowles, Ph.D., P.E., P.H.
Professor of Civil and Environmental Engineering
Director, Institute for Dam Safety Risk Management
Utah Water Research Laboratory
Utah State University
Logan, UT


[Abstract not available]

Evaluation of Forecast-Based Advance Release Strategies at Folsom Dam

Beth Faber, Ph.D.
Research Hydraulic Engineer
Water Resource Systems Division
Hydrologic Engineering Center
U.S. Army Corps of Engineers
Davis, CA


[Abstract not available]

2002 Sponsors