The three day rainfall maximum ranked eleventh on the list but the event produced much less flooding in California than some of the other events as its heavy rainfall was much less widespread. The bulk of the rainfall also fell well north of San Francisco.  However, the Modesto-Bee reported flooding near Eureka that sent 1000 people fleeing from their homes.  

02-05 January 1966 precipitation event

PW (mm) and normalized PW anomaly (magnitude of the anomaly scale is shown on the scale at the bottom of the figure)  valid 0000 UTC 04 Jan 1966.

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 0000 UTC 04 Jan 1966.

The pattern associated with this event did not follow the template of most of the other top 20 events.   Still, it was associated with a positive height anomaly at 500-hPa over Alaska and a strong negative one to its south.  However,  the negative anomaly was located a little farther to the north and east without having a southwestward extension to the negative anomaly.  Also,  there was no positive height anomaly to the south of the negative anomaly.  Therefore,  the pattern showed less of a southwesterly fetch than most of the events (see below) with the strong gradient being confined to the northern part of the state. .   The atmospheric river was much weaker than during the other cases and could not be defined as a strong river. 

The most unusual thing about this case compared to the others was the lack of strong PW anomalies (see below left).  The normalized 850 MF anomaly of 2.5 to 3 across northern CA suggests that a plume of similar magnitude will occur in a matter of a couple of months or sooner.  Despite the rather pedestrian normalized anomalies,  this event still produced impressive precipitation amounts on the CDC unified data set.  This suggests that moisture flux and PWs are not the only modulating factor governing precipitation amounts.  This was the weakest “river” of the 20 cases”    

Heaviest 3-day rainfall analysis using the CDC .25 deg by .25 deg unified data set ending 1200 UTC 05 Jan 1969.   

Precipitation analysis of  the  24 hours (in inches) ending at 1200 UTC 04 Jan 1966 from the .25 by 2.5 deg. unified data set.

Precipitation analysis of  the  24 hours (in inches) ending at 1200 UTC 05 Jan 1966 from the .25 by 2.5 deg. unified data set.