† Link to the introduction for The top 20 Greater San Francisco and Sacramento California cold season :†


This link provides the rational for using normalized anomalies and discusses how they might be used in the forecast process.† It is meant as an overview of the patterns associated with major California rainfall events.†

1) December 1964: This link provides a discussion of the event.† It was the top ranked event and produced a major flood in northern California with an estimated return period of over 50 years.†


3) December 1955: A major event,† produced a greater than 50 year flood event.†

6)† February 1986:† Ranked 6th on the list an was a major event that produced a record flood on the American River Basin and major flooding along other basins nearby.† The return frequency for the 10-day rainfall that encompasses this event has been† estimated at 1000 years

2) Jan-Feb 1963: Second ranked event, one that produced major flooding across the Carson, Feather American and Cosumnes River Basins.

4)† Dec 2002: The 3-day period ending at 1200UTC 16 December ranked fourth on our list which may reflect somewhat that the data coverage in 2002 was better than during some of the earlier events.††

5)† New Years 2006: Ranked number 5 which may be misleading because of† improved Quantitative precipitation.† This was a major event with significant flooding, the heaviest since 1997.†

7)† January 1974: ranked 7th,† most of the rain fell north of San Francisco.† Significant flooding occurred along Californiaís North Coast.†

8)† March 1995: major flooding along the Pajaro River Basin in Santa Cruz and Monterey counties.† These areas were declared Federal Disaster areas.†

9)† January 1995:† a major event, 42 counties in California were included in the Federal Disaster Declaration due to this extended rainfall event.†

†17)† New Years 1997:† This event probably should rank higher,† the three days totals implied by the HPC 24-hr precipitation analyses were higher than for the 1995 events and the amounts were more impressive than any other in a 10-year period ending in 2000. Major flooding occurred with the flood areas being† declared a Federal Disaster. Flooding associated with the event may have rivaled the legendary flood of 1862 (Roos 1997).

10)† November 1950:† This event and another in early December led to significant flooding in Yuba and Tulare Counties and led to flooding of the Tule River.† Roos has listed it as one of the nine big floods of note for California (2007).

11)† January 1966 event:† The bulk of the rainfall also fell well north of San Francisco.† The Modesto-Bee reported flooding near Eureka that sent 1000 people fleeing from their homes.† This was associated with the weakest atmospheric river of the 20 events.†

12)† January 1969 event:† The flooding was included in the Roos (2007) listing of major California flooding events.†† Significant flooding occurred over the Central Valley rivers, the reformation of Tulares Lake in San Joaquin Valley.

13)† December 1981:† The† Syracuse Herald-American had a story from the morning of December 20th stating that the stormkilled 3 people, raised 4 rivers to flood stage and produced mud slides.† However, compared to many of the events listed, the flooding during this case was relatively minor.†††

14)† November 1973:† No reports of serious flooding could be found from this 3-day rainfall event despite its ranking within the top 20 events within the data set.†

15)† Feb 1960: No reports of serious flooding could be found from this 3-day rainfall event despite its ranking in the top 20 events within the data set.† This suggests that antecedent conditions are an important player in determining whether major flooding will occur.†

16)† Jan 1970:† This event was a rather minor one in terms of significant flooding.† The only reports of flooding that could be found on the Internet were a report of flooding on Cache Creek of the Copay valley and an allusion to two boys being missing due to flooding Jan. 26 issue of the European Stars and Stripes.

18)† December 1995: The weather prior to the event had been dry which minimized the run off problems (Reynolds 1996).† As noted by Reynolds,† synoptically the pattern was very similar to the pattern that was present during the January and March 1995 events.

19)† February 2000:† December 1999 was the third driest December on record to south central California† which probably accounts for† the† lack of major flooding. Minor flooding was reported

21)† January 1980:† This event helped set stages for a later more significant flood event in February in southern California.† The synoptic pattern for this later SoCal event is shown.†

This website has been constructed to provide the synoptic patterns and normalized anomaly patterns of geopotential heights, 850 temperatures, precipitable water and 850-hPa moisture flux for the 20 greatest 72-hour rainfall events for the greater San Francisco and Sacramento areas since 1949 based on the CDC .25 x .25 degree unified precipitation data set.† A summary of the event,† itís synoptic pattern, and selected normalized anomalies are provided for each event.† The idea behind the site is that most of the extreme rainfall events in northern and central California are associated with strong atmospheric rivers or moisture plumes.† Rare events are not that common and the normalized anomalies can provide a rough estimate how often a similar moisture plume would typically occur which might provide a forecaster with some idea of the rarity of the event.† A forecaster or user looking at model forecasts of the synoptic pattern and associated normalized anomalies associated with a potential event could then compare model forecasts or ensemble mean model forecasts of anomalies with the historical major events and the patterns associated with them. Model forecasts with normalized anomalies are available at† http://www.wpc.noaa.gov/training/SDs/.†††† Farther down the road,† the hope is to developing a method for identifying possible analogs.††

Click on each link for the discussion of the events and to view the synoptic and normalized anomaly patterns.†

20)† March 1974:† .† An Army Corps of Engineer report was written that included flooding in March along the Russian River in northern California.† This was not a major flood event.

Acknowledgements:† This web page could not have been constructed without help from Rich Grumm and Mike Bodner.†