Monthly ECMWF Run

December 4, 2014

The monthly run of the ECMWF model was sure interesting today.  Here are the ensemble means of 500mb heights averaged for each of the next 4 weeks.

We already know what’s happening in the next week…warm and wet:

500za_week1_bg_NA

Then when it appears the cooler troughing offshore with moisture starts aiming cold systems at us the end of next week?  We go right into a split-flow pattern with the upper-level high building just to our north.

500za_week2_bg_NA

Check out the control run at 400 hours…about 17 days from now.  ecmwf_17dayanom  Sure looks like the terrible winter (for skiing) of 2004-2005!  Troughs and precipitation moving by mainly to our south in a southern stream of the jet.  The weekly average during that period looks like this.

500za_week3_bg_NA

About this point is where it gets interesting.  Here’s the last weekly average showing a similar setup too:

500za_week4_bg_NA

The control run shows two times where the upper level high is slightly farther to the west, allowing a push of cold arctic air down east of the Cascades and the Intermountain region, much like what we saw in mid November.  The first is around Christmas and then a week or so later.  I’d put the maps online but they are from WeatherBell and their latest policy is NO redistribution of ECMWF data, so I’m trying to cut back (sneaked one in there).

What does all this generally mean for the next few weeks?

1. Warm rains next week.  Most of next week the snow level will be above 5,000′.  Much of that time it’ll be above 6,000.  But we’ll see lots of 50-60 degree high temps in Portland too…October is coming back!

2. Turning much drier about 10 days from now, with below normal rainfall after that time.

3.  Ski areas COULD have a real rough time getting lots of slopes open as we head into Christmas Break.  BUT, as you know, just two good cold storms that sneak through and drop 12-18″ could get things going…pray for that.

4.  Around Christmas and beyond we could get real chilly again with strong east wind.  Not a big surprise that time of year of course.  In that forecast pattern and in the depth of Northwest winter, the cold would stick around for quite awhile too.

5.  Just having the upper level high to our north with wet systems going by to the south increases the likelihood of overrunning events (freezing rain) in the Gorge and possibly metro area as well.  We’ve already seen that several times (right now) and it’s only December 4th!

Of course all of this speculation is based on 1 MODEL RUN of ONE MODEL…but it’s fun isn’t it?

Chief Meteorologist Mark Nelsen