18-21 January 1969 event

The January flood  was primed by a 3 day rainfall event centered around January 12th.  The second extended rainfall event that ran from 1200 UTC 18 January-1200 UTC 21 January then produced major flooding . The flooding was included in the Roos listing of major California flooding events.   Significant flooding occurred over the Central Valley rivers, the reformation of Tulares Lake in San Joaquin Valley. Even worst flooding occurred farther south in the southern portion of the state where flooding along the Sespe Creek killed six hikers.    The figure below indicates the primary areas of flooding.  Note that the worst flooding occurred south of the San Francisco area closer to where the axis of strongest moisture flux.  

Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., Compilers, National Water Summary 1988-89-- Hydrologic Events and Floods and Droughts: U.S. Geological Survey Water-Supply Paper 2375, 591 p.

The synoptic pattern associated with this case was very typical of the pattern exhibited by most of the events.  A closed 500-hPa anticyclone was present in the vicinity of the Aleutians with as associated area of anomalously high heights.  A area of below normal heights were found to its southeast and southwest which helped produce a long a positive tilt to the associated trough.   A greater than 2 sigma negative height departure was located west of the California coast located far enough south to help tap into a strong atmospheric river. 

PW (mm) and normalized PW anomaly (top left),  850 winds (standard barbs and flags) and normalized 850 MF (top right),  500-hPa heights and normalized anomalies of the departure from normal (bottom left), and 700-hPa heights and normalized departures from normal avlid 0600 UTC 21 Jan 1969.   Magnitude of the normalized anomalies is given by the color fill from the bar at the bottom of each figure)

Note the greater than 3 sigma height departure  west of San Diego at 0600 UTC 21 January and note how it helps produce a implied southwesterly geostrophic flow ahead of the trough and how the an anomalously strong MF plume then stretched from off the California coast northeastward into Idaho. 

850-hPa winds (standard barbs and flags) and normalized anomaly of 850-hPa moisture flux (magnitude is given by the color fill from the bar at the bottom of the figure)  valid 1200 UTC 21 Jan. 1969.

The normalized anomaly of MF climbed to above 5 by 1200 UTC 21 Jan across southern California and the PW anomaly (not shown) to greater than 2. The high normalized MF anomaly suggested return frequency of having a similar moisture plume over that location would be over 24 months or given the  rainy season is confined to the cold season,  more the 4 years.   

Heaviest 3-day rainfall analysis using the CDC .25 deg by .25 deg unified data set ending 1200 UCT 18 Jan 1969-1200 UTC 21 Jan 1969.   

Large area 4-panel chart,  200-hPa heights and isotachs (top left), 500-hPa heights and normalized height anomaly (top right), 850-hPa heights and normalized temperature anomaly (bottom left), and 1000-hPa height and normalized PW anomaly (bottom right) valid 0000 UTC 21 Jan 1969.  The magnitude of the normalized anomalies are given by the color fill with the scale on the left had side of each panel.

Precipitation analysis of the  24 hours (in inches) ending at 1200 UTC 19 Jan 1969 from the .25 by 2.5 deg. unified data set.

Precipitation analysis of the  24 hours (in inches) ending at 1200 UTC 20 Jan 1969 from the .25 by 2.5 deg. unified data set.

Precipitation analysis of the  24 hours (in inches) ending at 1200 UTC 21 Jan 1969 from the .25 by 2.5 deg. unified data set.