Flooding Rainfall and Strong Winds on the West Coast

Energy continues to move ashore from the Pacific Ocean in the form of a low pressure system and its attendant frontal system. This will cause plenty of rain and scattered areas of thunder along the West Coast along with higher elevation snowfall. Another low pressure system will approach Sunday night with more rain and higher-elevation snowfall. A brief lull in the precipitation will occur on Tuesday before another low pressure system moves into Western Canada and its frontal system moves into the West Coast with more rain through the end of the week.

 

The first batch of precipitation. highlighted with moisture transport showing the areas of heavy rain at the leading edge of the transport.
Model agreement of the first batch of precipitation into the West Coast highlighted with moisture transport showing the areas of heavy rain at the leading edge and within the transport.
The second batch of precipitation starting Wednesday with moisture transport showing the areas of heavy rain at the leading edge of the transport.
Model agreement showing the second batch of precipitation into the West Coast starting Wednesday with moisture transport showing the areas of heavy rain at the leading edge and within the transport itself.
Forecast rainfall through early Thursday. Over 10 inches is forecast along the West Coast.
Forecast rainfall through early Thursday. Over 10 inches is forecast along the West Coast.

 

Through Monday, 2 to 6 inches of precipitation is possible from Central California to the Pacific Northwest. All told, from early Saturday through Thursday, when the second batch of precipitation moves into the West Coast, precipitation totals will be between 7 and 15 inches of liquid equivalent, with the best chance of reaching 15 inches along the West Coast and where thunderstorms occur. But it won’t be all rain because as the cold front enters the West Coast Saturday night, and lowers temperatures, more widespread snow will be able to fall in the Cascades, Sierras and Inter-Mountain Region. Strong winds and snow accumulations totaling 1 to 4 feet, especially in the Cascades, will be the main threat to the higher elevations. Wind gusts could reach 60 miles per hour through early Monday in the higher elevations. Strong winds and flooding will be the main threats to the lower elevations especially in the areas of Southern and Central California where tougher ground as a result of the continuing drought will not allow as much seepage of the rainfall into the ground. As a result, there may be standing water on roadways, near poor drainage areas and streams may spill over their banks, especially with the continuation of the heavy rain and heavy rain in short periods of time. Because of these hazards, numerous Flood Watches and warnings have been issued especially within California through Sunday, numerous high wind warnings and wind advisories have been issued mainly in California, but also into the Central West Coast and Southwest through Sunday. The Sierra Mountain Range also has a Winter Storm warning through Monday.

Forecast snowfall. Notice the higher amounts over the Sierra Mountain range.
Forecast snowfall. Notice the higher amounts over the Sierra Mountain range.
Zoomed in wind gust forecast over Northern California with areas of 30 mph gusts in the lower elevations and 50 to 60 mph gusts in higher elevations.
Zoomed in wind gust forecast over Northern California with areas of 50 to 60 mph gusts. 
The drought monitor showing the exceptional drought conditions in southern California, further exacerbating the flooding situation.
The drought monitor showing the exceptional drought conditions in southern California. This will further exacerbate the flooding situation.
Watches, warnings and advisories for weather impacts through Monday.
Watches, warnings and advisories for weather impacts through Monday.

 

Even with these high precipitation totals, only the overnight precipitation is abnormally high and from a strong low pressure system. All the other precipitation and resulting weather impacts, like flooding, are a result of continuous precipitation over the region. This is not to say that continuous precipitation is not worthy of taking note, but that the storms that cause the precipitation themselves on a whole are not worthy of taking note.

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