Wet Snow on Sunday Morning over the western lowlands, and a major forecast bust in Portland.

 Frigid air has settled over the region, with the low temperatures today ranging from the mid-20s over the western lowlands to the teens and single digits in the Columbia Basin (see below).   Temperatures dropped to below zero F over some valleys east of the Cascade crest.

The whole region is plenty cold enough for snow right now, there just isn't any moisture.

All the moisture is going into California right now.   Good...they need it!

Friday and Saturday will be generally dry over the Northwest, with plenty of sun.

But Saturday night, a moisture source will approach:  a Pacific occluded front (see forecast map for 7 PM Saturday night, black lines are sea-level pressure, the front shown by a red line, the near-surface temperature in color shades).

The front will bring moisture and warming, but the latest model simulations suggest that cold air will hold in enough in central Puget Sound to produce a few inches of wet snow on Sunday morning (see UW model forecast accumulated snowfall through 4 PM Sunday).

Lots of snow in the mountains.

With temperatures on the edge, expect less snow near Puget Sound.

The European Center model is going for less snow near the Sound...around an inch.

The Portland Forecast Bust

As good as weather prediction has become, sometimes the results disappoint.  

And forecast skill is rarely more problematic than for Northwest snow.  Not only are temperatures often marginal for snow, but small errors in precipitation intensity can have HUGE impacts on snow forecasts.

Keep in mind that a tenth of an inch of precipitation in the form of water will result in roughly ONE inch of snow.  A roughly ten-to-one ratio.    So small errors are amplified.

Here are the snow totals from yesterday in the Portland area.  Around 8-10 inches around the city.

In fact, Portland's airport received 10.8 inches, resulting in the second snowiest day in the station's history.

How much was predicted?  The official National Weather Service forecast Tuesday night was less than an inch! (see below)

A major issue was that the models underplayed the moisture circulating around a low moving down the coast, with a band of heavier precipitation hanging around Portland (see satellite image around 3 PM yesterday).  Hard forecast.