Substantial Improvements in Western U.S. Snowpack and Water Resources

Some folks call it a March miracle...while others call it a La Nina winter....but in any case there has been large amount of new snow in the mountains from California's Sierra Nevada to the Oregon Cascades, which has greatly improved the snowpack situation.

First, compare the snowpack of March 4th against January 6th.   Washington is all green (near normal, 90-109%) or better, Oregon has gone from red (<50%) to orange (50-79%), as has much of northern California (click to enlarge). Northeast Washington, northern Idaho, and much of Montana are well above normal. 

Substantial parts of the Sierra Nevada have gotten 6-8 feet of new snow this week.

Reservoirs are in good shape.   Here is Washington, the Yakima River Reservoir system is hugely above normal (see plot), in fact, as full as would be normal on May 1. 

In California, the reservoirs are all at or above normal, except for the damaged Oroville reservoir that is being kept partially filled.

West Coast precipitation is not finished with us, and the next week or so should bring plenty more.  The total precipitation forecast for the next 11 days (shown below) from the NOAA/NWS GFS model indicates plenty of precipitation ahead, with 5-10 inches of liquid water in terrain from the Sierra Nevada to SE British Columbia. 

The pattern that has kept us wet has been persistent troughing over the West Coast, with high-pressure offshore. Here is an map showing the differences of 500 hPa (around 18,000 ft) heights from normal for the last week. Purple and blue over the west coast (a trough or low pressure), but red/orange (high pressure) offshore.

The trough should move westward, resulting in moist, southwesterly from CA to BC ) see forecast map for Monday, March 13 at 5 PM below).  That is why the northern half of the West Coast will be wet.

 The bottom line of all this is that water supplies from central CA to southern BC look good, and we should be in good shape for the upcoming summer.