Super Moisture Plume Headed for the Northwest.

Many of you will need umbrellas during the next week.   And perhaps a lightning rod.  

The cause? 

A dramatic plume of moisture will be heading into the Northwest from the south.  

Southwest Monsoon moisture will be entering our region, and our chances of breaking any dry spell records are dimming fast.

The latest water vapor satellite image shows the impressive moisture plume over the Southwest---and it is heading our way.

Let me start by showing you the latest precipitation forecasts from the UW WRF model.  For the 72 hours ending 5 PM Tuesday, the interior gets wetted down well, with some favored locations enjoying over an inch of rain.  This precipitation is from the plume of moisture from the southwest U.S.  

But our wet bounty is not over: during the next 48 h the first Pacific disturbance of the season moves in from the west and provides precipitation for western Washington and southwest BC. This system is a bit earlier than normal (normally the first wet system occurs during the third or fourth week of August), but no one is going to complain.

Now back to the superplume of moisture coming up into our region.  

Below is the forecast total moisture in the atmosphere predicted by the European Center model for Sunday evening. Known as precipitable water, it represents the depth of water that would occur if all water vapor was condensed out of the atmosphere.  The colors represent the percent of normal.  Blue is high (over 160% of normal, gray is VERY high (over 250% of normal).  Lots of moisture moving northward east of the Cascade crest.

How unusual is this moisture plume?  The predicted values over eastern WA and southern BC on Monday morning will be up to FIVE standard deviations from normal for that date (see image below, dark gray).  A standard decision is a measure of deviation from the mean.  Five standard deviations indicate essentially unprecedented conditions over the past several decades.

So we will go from extreme heat to extreme moisture in a little over a month!

This moist air will be relatively unstable, which means a good chance of thunderstorms east of the Cascade crest.   The simulated infrared satellite image on Saturday night suggests a number of storms in eastern Oregon (see below).  Thunderstorms can bring needed rain, but they can also start wildfires.

With the lack of thunderstorms and wind, wildfire activity has actually declined in recent days.  So this situation will be one to watch carefully.

Reminder:  new podcast tomorrow morning.  Perhaps it is time to talk about Northwest thunderstorms!