Major Transition to Warmer and Wetter

It is about time.    A major transition in the atmospheric circulation is occurring over the eastern Pacific that will lead to much warmer and wetter conditions over the Northwest.

Eastern Washington will get out of the endless deep freeze.

Portland will finally warm up enough to rid itself of the icy roadways that have has made driving like a segment of Ice Road Truckers.

Western WA will lose the blue skies and bright sunshine that has been so pleasant for suffers of Seasonal Affective Disorder.

And tragically, Cascade skiers, particularly on the lower slopes, will give up powder conditions for the familiar Cascade Concrete.

Will the History Channel film a segment in Portland?

And there is a major threat tomorrow and in the Columbia Gorge:  an ice storm from freezing rain.

The origin of our unusual cold has been persistent high pressure east of the Cascades that has brought cool, dry easterly flow over much of the region.  A disturbance going south of that high gave Oregon the snow earlier this week.

To show you the changes, here are upper level (500 hPa) maps that illustrate the change.  In the first (for 4 AM Monday), an upper-level ridge is right over us, resulting in dry weather over the region.

In contrast, by 8 AM on Wednesday, the ridge is far east of us, a trough has developed over the eastern Pacific, and moist, warm southwesterly flow is over our region.

The map for 4 AM Friday is amazing...a nearly strait jet stream is directed towards southern California (remember, winds are parallel to the height lines and the wind speed is proportional to the gradient of the height lines).

A HUGE change is going to occur over eastern WA and Oregon, which has been locked in the freezer for weeks.  To illustrate, here are the temperatures at Pasco for the past four weeks (yellow lines), with the normal highs and lows indicated by the red and blue lines.  For virtually all of 2017, Pasco has been well below normal, with the highs on most days not even reaching the normal minima, and a number of hours below zero F.

Another way to see how extreme things have been..here is the deviation of the average minimum temperature from normal for the past month over our region.  From the Cascade crest eastward to the Rockies and beyond, some areas have had minimum temperature 15F below normal or more...virtually all  of that region is a least 9F below normal.  Stunning.

But all this is going to change... in fact, is changing.  Here are the predicted surface (2-m) air temperatures from the European Center model, valid for Hanford, Washington.  A major warming is predicted over the next two days.  Temperatures in the 30sF will feel like spring for the those chilled folks in the Columbia Basin.

What about Seattle and Portland?  The forecasts will warm your heart and your extremities.  Portland temperatures will climb into the forties on Tuesday, as will Seattle's.

Seattle is already in the mid-40s and it feels so mild.

And did I mention precipitation?   We are going to be very wet for the next few days, with the latest high-resolution WRF run suggesting that over the next 72 h as much as 5-10 inches of liquid precipitation will fall in the mountains--most of the that will be rain, except for the higher elevations of the Olympics and north Cascades.

And now we must talk about a problem:  a real threat of freezing rain in Portland on Tuesday during the transition.   It will take a day or two to scour all the cold air east of the Cascade crest and during the interim, some of which will move eastward into the Columbia Gorge towards Portland.  Warm rain from below will drop into this cold air and be chilled, resulting in freezing rain that will freeze on contact.    The NWS has an ice storm warning out for the Columbia Gorge region and Portland.

Over the next 7 days, the National GFS model forecasts suggest a LOT of precipitation along the West Coast (see below), with 5-10 inches being common over West Coast terrain.  As I will describe in a future blog, the West Coast drought is history.  Good for veggie prices next year.

The sun has been nice, but it is time to get back to normal for a while.