Rain Arrives, In the Valley and Cascades Too

December 27, 2011

Here are the rainfall totals so far today…for all of us it’s the heaviest we’ve seen the whole month.  And this map only tells part of the story

In the mountains, both west and east of the Willamette Valley, the precipitation has been far heavier. Lee’s Camp, along Highway 6 in the Coast Range, has seen 4.90″ as of 11pm. And the snow earlier today in the Cascades has changed to all rain.  Timberline Lodge’s total today (so far) is 2.40″, most of that as rain.  In the past 4 hours more than 1″ has fallen…not good for the thin snowpack.  Timberline has cancelled their night skiing both tonight and tomorrow night due to the conditions.

The heavy rain continues in the mountains tomorrow as a new slug of moisture arrives and sits over us most of the day.  Thursday the band moves farther south, then late Thursday night and early Friday we get one last cold front moving through.  There is good news for skiers though!  The trend the last few model runs today has been for a sharper upper-level trough coming behind that last cold front Friday.  850mb temps drop to -5 to -7 by Friday afternoon and evening.  The precipitation will be tapering off, but the transition to colder air plus leftover moisture could leave 6-10″ new snow before we finally dry out.

It was a challenging long-range forecast this afternoon due to  the GFS and ECMWF differences.  The ECMWF was totally dry Saturday through the middle of next week with a strong upper-level ridge developing overhead.  The GFS was weaker with ridging and showed a few rainy systems coming through.  Luckily we gambled on the ECMWF and now the 00z GFS has turned much drier.

Wind this evening turned out even weaker than I expected, no gusts to 40 mph here in the metro area and now the gradient is weakening.

A look at the VERY long range (10+ day maps) shows no sign of cooler than average weather.  Here’s the new 00z GFS ensemble 850mb chart.

Above average for the next 8 days or so, then closer to normal beyond that.  The 00z ECMWF has ridging of some sort over us through the next 10 days.

Chief Meteorologist Mark Nelsen