Replenishment: Heavy Precipitation over Northwest Mountains Ensures Summer Water

A series of very wet storms, coupled with sufficiently cool temperatures to allow large snowfalls in the Cascades, is about about to push Northwest water resources to near normal, providing us with some confidence that there will be sufficient water supplies in the Northwest next summer.

Before I talk about the storms, lets review the current water situation (see graphic of snow water content across the west). Washington State is around 75% of normal, the Oregon Cascades about 45%, and the recent storms have brought the Sierra Nevada up to around 45%.   We are in a far better situation than two weeks ago.  The Rockies are doing quite well, which is quite important since the Colorado River headwaters are in fine shape.

But the heavens are about to open up over the Northwest as a persistent moist southwesterly flow will bring a series of very wet systems into the region.

Right now, at 10:30 AM on Saturday, weather radar shows the next approaching system, with the yellows indicating heavy precipitation. Northwest Oregon is already being drenched and Seattle is about to get wet.

Here is the 72 hr forecast  rainfall and snowfall maps, based on the UW WRF model.  Impressive totals (5-10 inches) in the Olympics and Cascades, and importantly, northern CA gets a piece of the action.

 The snowfall maps for the same period will bring a smile to skiers and water resource managers, with 2-3 feet over the mountains of BC and the Washington/Oregon Cascades.  Having lots of precipitation in BC is good news for the NW, since that is where the Columbia headwaters are located.

This 72 h totals above includs precipitation from the storms coming in today and late Sunday.  But other strong/wet storms are forecast to reach us on Tuesday and Thursday, so lets look at the subsequent 72 hr totals.  Mama Mia!  It almost looks like a repeat, with a bit less getting into California.

The reliability of our forecasts for the large-scale storms associated with the above precipitation totals is far greater than the frontal waves of last week's local snows...so it would be surprising if we don't get inundated as shown above.  The NW River Forecast Center is predicting serious flooding on some western Oregon rivers.

The latest forecasts suggest high pressure will move in on Friday and Saturday, with cooler conditions aloft.  I would expect extraordinary skiing conditions then...so get ready.  By that time I would expect the Washington snow pack to be near 100% of normal, leaving us in great shape for the upcoming summer, assuming normal or even a bit below normal precipitation the rest of the season.  But keep in mind that such a snow dump could lead to dangerous avalanche conditions in uncontrolled areas, so please check with the NW Avalanche Center's forecasts and warnings.

 California's situation will improve, but they still need more major storms.

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The NW Weather Workshop is the big annual gathering of those interested in the weather of the Pacific Northwest and everyone is welcome.  For more information, including the agenda and registration information, please check out: https://www.atmos.washington.edu/pnww/