A Remarkable Mini Atmospheric River Hits Western Washington

Most of the time, atmospheric rivers--plumes of lower-atmospheric moisture from off the Pacific Ocean--are relatively wide and thus produce large amounts of precipitation over a broad region.

But on Friday, something relatively unusual occurred:   a very narrow "mini" atmospheric river was locked over our region for hours, producing a narrow band of intense precipitation over western Washington and into the Cascades.

You can really see it in the regional weather radar image for Friday morning (below).  Yellows indicate the heaviest precipitation.

The southwest-northeast plume of heavier rain was very evident.  Totally dry over the San Juans and the southern Cascades.

  

Consider the precipitation totals on Friday below (only values more than a third of an inch are shown).

You can clearly see the precipitation band; where the moisture plume was forced to rise by the central Cascades, 3-5 inches fell.

Local rivers have surged, some to near flood stage.  The black dots below show the rivers that are now experiencing MUCH above normal flow.

Ironically, this is the area that the wacky Drought Monitor graphic shows SEVERE DROUGHT.

The UW WRF model accurately predicted this moisture plume the day before.   Below is the prediction (for Friday morning) of water vapor flux (the amount of water vapor brought in by the wind).  Orange shows the highest amounts.    Not bad.   

The model precipitation total (through 4 PM Friday) was excellent:  here is the proof:

We have come very, very far in our ability to predict local weather.  Really stunning.

This is something the gloom and doom global disaster folks don't seem to understand:  we now have the ability to predict and prepare for severe weather.

My colleagues in the National Weather Service recognized the situation and put out a flood advisory yesterday morning for the moisture plume area.

For those of you (like the Seattle Times) who are worried about drought conditions and lack of water for our region, the plume of precipitation made a direct hit on Seattle's Tolt Reservoir, where almost four inches have fallen:

Reservoir levels are moving up rapidly as a result.

Apparently, this has gotten some folks nervous.

More rain is coming later Sunday and Monday. Sorry...this IS November.

A Near "Bomb" Cyclone Approaches the West Coast

 Last weekend, I started getting emails from folks concerned about a "bomb cyclone" approaching Washington state.    Some of the amateur Facebook and YouTube sites were also starting to beat the weather drums.

The reason?  Several model runs at that time had scary forecasts, such as this one for 4 PM Thursday (tomorrow).  The kind of strong low that would easily take out power to hundreds of thousands of local customers.

When I took a look at the situation, I realized the uncertainty of these forecasts was very, very large:  the ensembles of many forecasts have a huge spread in solutions, and the forecasts changed radically run to run.

That is why I did not blog about it.  

We are close enough now to have a good idea of what will occur tomorrow... the rapid development of a strong low off the California coast. 

A low center that will dissipate almost as quickly as it developed.

Here is the pressure analysis for 4 AM this morning.  An amorphous 1002 hPa low-pressure center off of northern California.  Yawn.

Now look at the forecast for 4 AM Thursday morning:  a 986 hPa low has formed.  Impressive.

A deepening of 16 hPa in 24 h.   Not quite the bomb rate (24 hPa in 24 h), but very substantial.

The developing low was quite evident on the visible satellite image this afternoon (see below, and I marked the low-pressure center).

The water vapor satellite imager tonight (8:30 PM) was quite impressive:

By 10 AM on Friday, the low will weaken to 1001 hPa and drift nearly due south.

This storm is predicted to drive some large waves offshore (see wave forecast for 4 PM Thursday), with some getting to 25 feet, and some modest waves reaching the coast.  No big deal.

Here in Washington State, we will get little wind from the low center.  However, it will push a plume of moisture into our region (yes, an atmospheric river) that will provide more welcome rain (see forecast of the water vapor transport below).

The forecast totals through Sunday at 4 AM are impressive in the mountains: