Potentially Historic West Coast Precipitation Event

There is the potential for a historic atmospheric river (AR) precipitation event between 1 - 4 December 2012 along the U.S. West Coast. The impact guidance precipitation products associated with the top 15 most similar historic events (located here) based on the 20121128/0000F096 GFS forecast show very high chances for another extreme event (potentially more extreme) in this area.

The current Hydrometeorological Prediction Center's precipitation forecast is very similar to the above analog impact guidance and to many of the historic precipitation events in the top 15 analogs (shown in thumbnails below HPC forecast).

The 72-h and 120-h median and >7" probability precipitation guidance (above) from the top 15 analogs show this heavy-precipitation potential. In addition, the 120-h precipitation thumbnail maps show that the majority of the top 15 analogs were associated with extreme precipitation events.

The thumbnails (located here) allow the forecaster to see that many of the individual analogs are historic West Coast AR events...they are listed here with their NCDC impacts. Being able to analyze the impacts associated with these events is one of the very powerful aspects of the CIPS Analog Guidance.

16 December 2002 (impacts)
31 December 1996 (impacts)
2 January 1997 (impacts)
9 December 1996 (impacts)
15 November 1981
11 January 1995 (impacts)

Some of these events are mentioned on the ESRL Notable Atmospheric River Events page (located here). The following is a screenshot from the impacts of the 31 December 1996 event from the ESRL page.

It is clear that the impacts from many of these events were catastrophic to this area. Although these analogs can and may likely change as the event approaches, given the relatively good agreement between deterministic and ensemble model guidance along with the analogs...a high-impact precipitation event is likely along the West Coast.