A "Dirty Ridge" is Coming to the Northwest

No, this is not some kind of meteorological pornography.

A "Dirty Ridge" is when moisture, often accompanied by clouds and precipitation, makes its way around the northern portion of a high-pressure area ( ridge is another name for high pressure).    

Wet conditions with high pressure, not some type of obscenity.

Before I start, some review. Low-level winds typically rotate clockwise around higher pressure areas (see below). Thus, winds are southerly on the western side of the high and westerly (from the west) on the northern side.

You can see this windfield around the forecast high at 7 PM Friday night (below, for the 850 hPa level, about 5000 ft above the surface).

Consider a forecast map for 7 PM on Friday of sea level pressure, surface wind (arrows), and the transport of water vapor by the wind (shading, called integrated water vapor transport).

Strong winds from the southwest and west on the western and northern sides of the high draw moist air northward from the subtropics around the western flank of the high and moves it eastward over the northern flank of the storm.   The clouds and rain are the "dirt" of the dirty ridge.

Fast forward to Tuesday morning (March 10), and the high is still offshore, and moisture continues to move around its western and northern flanks  (see below).

This circulating moisture will be forced upward by local mountains, resulting in precipitation (the 72-h precipitation ending 5PM Sunday is shown below).  

Considering the relatively low snowpack over the region (about half of normal right now), this precipitation will be welcome, even if it is associated with a dirty ridge

With Rapidly Strengthening Sunshine: High Temperatures are Possible in March

 If the sun feels stronger to you right now, it is not your imagination.   

And this stronger sun and longer days can result in spikes of warmth during the month of March in our region.

First, let's consider the average solar radiation in Seattle over the year (below).  Late February, March, and April are times of rapidly increasing solar radiation at our latitude.

Of course, there are clouds, which reduce surface warming, but even so, March is a time of rapidly increasing solar radiation reaching the surface, as shown by the observed solar energy in 2019 (below).   

As a result of the increased sun (and generally decreasing cloudiness), we can get some amazingly warm days in March.  The plot below shows this year's temperatures (blue bars) and record highs (red) and lows (light blue).

Some March days have gotten as high as 80F, with many in the 70s.    You will also note that the chances of getting really cold (below 20F) end by March 10th.

So, will you get a taste of this welcome warmth this week?   Monday will be the warmest day, with rain and cooler conditions by midweek.

The European Center model is going for 58F on Monday, similar to the UW system.

But the warmth will vary over the region, as shown by the temperature forecast for 4 PM on Monday over Washington State (see below).  Temperatures will exceed 55F over central and southern Puget Sound country and in the lower elevations of the Columbia Basin.

Some isolated lucky folks (e.g., near Olympia) will get to 60F.    

I am planning a nice long run late Monday afternoon...which should be wonderful