Case Study 008"California
Flood"
31 December 1996
This case focuses on the California flood which occurred 31 December 1996 to 5 January 1997. The data used for this were presented as a laboratory exercise during the Hydromet 97-1 residence course held at COMET in April 1997.
THE COMPLEX INTERACTIONS BETWEEN SYNOPTIC AND MESOSCALE METEOROLOGY, GEOGRAPHY, AND HUMAN ACTIVITY DURING A MAJOR WEST COAST PRECIPITATION EVENT:
31 December 1996 - 3 January 1997
Learning Objectives: To understand the synoptic, mesoscale and storm-scale interactions that result in noteworthy flood events along the Pacific coast.
1. Understanding the uses and limitations of available tools.
2. How orography may contribute more than upslope and downslope.
3. The details one must pay attention to that go beyond the "composite" guidance
4. The role of strong low-level forcing in precipitation production.
5. The role of jet dynamics in these types of systems.
6. The role of human activity and structures in flood events.
Materials:
1. Depiction of low-level features on 1 January 1997 at 0600 UTC (sfc plots, 850 mb heights, precipitable water).
2. Depiction of upper level features on 1 January 1997 at 0600 UTC (water vapor imagery and 500 mb heights).
3. Maps of northern California with topography and radar sites.
4. Maps of northern California with topography, counties, and 7 rivergauge sites, and stations.
Assignment, Part 1
1. View the various data from 0000-0600 UTC 1 January and model guidance from the 0000 UTC model run. What state will receive the most precipitation between now and 1200 UTC 2 January?
2. What might be the primary forcing mechanism?
3. Where would jet dynamics suggest the heaviest precipitation? Will it be there? Why or why not?
4. How do you expect the model guidance to perform?
Additional Material
1. Map of northern California with rain gauge reports for 48-h amounts ending 0000 UTC 1 January.
2. Plots from 7 river/reservoir points.
3. Text messages from the Sacramento WFO.
Assignment, Part 2:
1. Review any data up until 1200 UTC 1 January, including 1200 UTC model guidance.
Why would the northern end of the valley (i.e. Shasta County) get as much, or more, precipitation than mountain ranges perpendicular to the southwest flow?
2. Is this where the jet dynamics suggested the heaviest precip?
3. What may be enhancing the intensity of precip?
4. Do you think the Feather River will top the levees near Yuba City (YUB)? How about the Sacramento River near Bend Bridge (BDB), or the Truckee River (FAR)?
More Material:
1. River Stage plots through 3 January.
2. Rain gauge reports for 1-3 January.
Final thoughts:
1. Does it appear the Feather River levees near Yuba City survived?
2. Would any strong westerly component into the West Coast be a major event?