Heavy Rainfall, Eclipse Weather, and Possible Saturday Windstorm

Today we had an active atmospheric river over western Washington and Oregon, producing some impressive one-day totals.  Take a look at the total precipitation for the 24-h period ending 8 PM on Wednesday (see image).  Some locations (such as near the SE side of the Olympics) have reached over 4 inches, while 2-4 inches was widespread over terrain.  Only portions of eastern Washington received less than .05 inches.

The 24-h rainfall amounts from Seattle Rainwatch, based on the Camano Is. radar, shows a huge contrast in western Washington, ranging from 2-3 inches in the southern Sound to roughly half that north of Everett.

An infrared satellite picture at 1 PM his afternoon shows the plume of moisture extending into our region, and lots of unstable air behind it over the Pacific, which will be moving in tomorrow.

The partial solar eclipse

A partial eclipse of the sun will occur tomorrow (Thursday) afternoon starting at 1:36 PM and ending at 4:20 PM here in Seattle.  Will it be clear enough for you to see it?

Here is the UW WRF model's cloud forecast for 3 PM.  Best place to go for a chance for clear skies?  The eastern slopes of the Cascades.

And finally, I and others have been watching the potential storm on Saturday.  The solutions have shifted a bit, but right now it looks like we will have a decent blow on Saturday night, but not an historic windstorm.

On Saturday at 11 AM, the pressure forecast shows a strong, but elongated low off the Washington/Oregon coast.  Elongated is not good...you want a compact, concentrated storm.  But there are large pressure gradients along the northern CA and southern Oregon coasts--40-60 mph gusts are possible

 By 2 AM on Sunday the low has passed into southern BC and a large pressure gradient is over western Washington.  Expect wind and some power outages, particularly since leaves are on the trees.  Still plenty of uncertainty with this storm, so will watch it carefully.

Heavy Rain Coming and Windstorm Threat

An atmospheric river, a warm current of large amounts of water vapor, will be approaching our region starting later tomorrow (Tuesday), but it will be coming from a less frequent direction:  the west.  And the result will be the heaviest rainfall to strike our region since last winter.

Time to replenish our renowned water resources!  And a good reason to be glad you don't live in California.   And speaking of parched California, they are going to get a piece of the action.

Let's start by looking at the latest view from space, showing the amount of moisture in the atmosphere.  Reds and purples are large amounts, and not surprisingly such enhanced values tend to be in the tropics.   But a huge northward push of moisture is occurring in the central Pacific and a tendril of it is moving westward towards us.    It has our name on it.

Let me show you the forecast atmospheric moisture for 2 AM on Wednesday morning.  You can see the heavier moisture (blue and white) heading towards us.   And when that moisture is forced to rise by our regional terrain, there will be lots of precipitation.

How much?  Here is the forecast from the UW WRF model for the 72 hours ending 5 AM on Thursday.  Big values (more than 5 inches in the Olympics, North Cascades, and northern Oregon coastal mountains. An inch or two in the lowlands.   Rake the leaves from the drains near your house or apartment!

The next 72 hours?  Still wet, but less so.  1-5 inches over the region west of the Cascade crest.  One good thing:  northern California will get enough rain to begin to fill their thirsty reservoirs.

As with most atmospheric rivers, there will warm temperatures and strong, but not damaging, winds (30-40 mph on Tuesday night and Wednesday AM).  To illustrate here are the forecast temperatures, heights and winds near crest level (850 hPa, about 5500 ft) on Tuesday at 11 PM.  You see how packed those height lines are approaching the Oregon/WA coast....those are associated with strong SW flow.  Reds are warm air.

Let me make clear...this is NOT going to be a record event.  But it will be the wettest period since last winter.

Finally, a number of the modeling systems are predicting that a deep low pressure center will approach our coast on Saturday morning.  Here is the solution from the U.S. GFS model (the solid lines are isobars, lines of constant pressure) for 8 AM Saturday.   Huge pressure difference (gradient) along the southern Oregon coast...with big winds (50-75 mph).  The European Center model has the same low, but fuarther north and offshore.   It will take a few days for the solutions to stabilize...but this is worth watching.

The latest run is in...and it is getting more threatening for western Washington!   This is valid 5 AM Saturday.  Only a 108 hr forecast...close enough that you got to be concerned.  985 hPa low.  This would be a major windstorm folks.

Here is pressure and sustained winds (kts) for the same time.   Wow...serious winds along the coast.

And by 10 AM Saturday, the low moves north of Puget Sound after crossing the Olympics...the most threatening windstorm path.  I am going to COSTCO tomorrow to buy batteries.