Wet December - Will it continue?

December has been off to a WET start!  Some may be wondering if this will continue through the month.  We will address some of the impressive numbers so far this month and also take a peak into the future.

So, how wet has it been?  Here is a map showing total precipitation from December 1st through the 10th for selected areas.

Quite the impressive precipitation totals especially in the Cascades.  Some locations on the west slopes of the Cascades have received amounts in excess of 10 inches.  It's also been wet in the Idaho Panhandle with Mullan Pass coming in with 6.70 inches, and 5.38 inches in Prichard.  

So how do some of these totals compare to normal?  Well these amounts only cover ten days, so its no surprise that these totals are well above normal.  Take a look at the values below.

So what has caused this abnormally wet period.  The answer is a very strong and active jet stream that stretched across the entire Pacific Ocean which brought numerous storms into the area.  

NCEP reanalysis of 300mb zonal mean wind Dec 1st through Dec 8th, 2015

So what does the future hold in store?  More active weather is in store with the parade of storms persisting.  Let's begin with Saturday...

     18z/11th GFS forecast of 500mb height and 700-500mb Relative Humidity
4 PM Saturday

The bright screen shading on the map is indicative of high moisture content in the atmosphere.  A deep low pressure system is located near Vancouver Island.  This storm is expected to bring snow to the Cascades and northern valleys and mountains.  Locations from Interstate 90 south from Ellensburg to Lookout Pass are expected to see mostly rain in the valleys with snow in the mountains.

So how about Sunday?  

18z/11th GFS forecast of 500mb height and 700-500mb RH 10 AM Sunday

You can see the wet weather continues with the best focus of moisture (with valley rain and mountain snow) over Oregon, Southeast Washington, and Idaho. This day could bring significant snow to the Blue Mountains, Camas Prairie, and Lookout Pass areas.

After this the pattern turns cooler and drier with a potential weak system Tuesday night bringing light snow to the Idaho Panhandle.  But after that models show potential another wet storm on or around Thursday.  

18z/11th GFS forecast of 500mb height and 700-500mb RH 4 PM Thursday

It's too far out to have much confidence in the specifics for this storm, but more rain and snow looks like a good bet.  Beyond this forecast confidence drops, but long range outlooks from the Climate Prediction Center for Dec 19th through Christmas day are favoring elevated chances of wetter and cooler than normal conditions.  

Overall it looks like December is going to finish out much wetter than normal.