Wet Week in the West and Snow Hits Washington State

Recent newspaper articles talk about a prediction for dry conditions in the western U.S. over the winter, but the atmosphere this week has other ideas. 

Today, a hurricane is moving through the southwest, a frontal system is hitting California, and a weaker system is moving through Washington State (see pic below).   It is hailing outside as write this.

Want to be really shocked?  It is snowing at Steven's Pass, where the temperature is 32F.  Don't believe me?  Check out the latest picture from the WSDOT cam there.

The WRF model forecast for cumulative precipitation over the next week (through 5 PM next Tuesday) is mighty soggy, with rain over the entire domain.  1-2 inches in part of Washington and previously dry Utah gets hammered with up to 5-10 inches in places.  Northern California is wet.  This rain event will be the end of most western U.S. fires.

As noted in the media, we just finished our "water year"-- which runs from October 1 through Sept 31 each year.  In some ways, this period is our natural precipitation period, since October 1 is roughly the start of the time when rain is significant around the Northwest.

Our recent water year (2017-2018) at Seattle was above normal by about 3-4 inches (see cumulative precipitation chart, light green is normal, dark green is cumulative amount above normal)

And  the previous water year (2016-2017) was even wetter than normal!

To put it mildly, we have not been in drought the past few years.

The extended forecast of dry conditions is heavily dependent on the projection of a weak to moderate El Nino for this winter, with low pressure offshore.

 However, the patterns of the last few weeks and the upcoming week are very different...in fact, very La Nina like.  A characteristic of La Nina winters is a ridge offshore, with northerly, cool unstable flow over our region.

The upper level pattern this afternoon shows an upper trough pushing over Washington.  In January we would be talking about lowland snow with such a pattern.

Another trough on Friday, and this will be a wet one

 High pressure builds offshore during he weekend and a very deep trough will bring cold temperatures into the southwest.

 And next Monday evening, the pattern continues, with weak disturbances over our region.

So forgot warm/dry conditions for the next week.  Showers and cool temperatures will reign over the Northwest, with more sun from Saturday onward.



from Cliff Mass Weather and Climate Blog https://ift.tt/2Nj4vCy