More Serious Rain Returns

 It has been cool, and there has been some light rain over western Washington.   Several of you have emailed me, asking when we will get more serious moisture.

Your answer is below.

Let me show you the latest European Center precipitation forecast for our region.  From 11 AM today through 5 AM Friday, there is light rain over the region, with moderate rain over the mountains.

With winds from the west, the eastern slopes of the Cascades will be rain-shadowed.

Then the rain picks up as a trough of low pressure moves through over the weekend, with the totals through Sunday morning exceeding 1 inch over the western slopes of the mountains.  Saturday might not be a good hiking day.

 The totals steadily increase through Tuesday morning.

You will notice that the precipitation will be relatively light over the lowlands of western Washington. Why?

This is because the winds often blow from the west this time of the year, which tends to produce downslope flow and drier conditions downstream (east) of our generally north-south terrain barriers.

This is illustrated by the winds around 5000 ft on Friday morning below.

During the winter, winds are more southerly, allowing more precipitation in the lowlands.

This type of pattern also produces large temperature contrasts across Washington State.

Consider the situation on Saturday at 5 PM.  Temperatures are in the low 50s in western Washington, but around 70°F in the Tri-Cities.  So head across the Cascades if you want some springtime warmth.