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.