July 29, 2021

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!


19 comments:

  1. Trying to share this forecast with my sister, who lives in the drought region of E. WA. and facebook is blocking the share.

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    1. Just cut and paste the blog from his site. Here is the latest: https://cliffmass.blogspot.com/2021/07/monsoon-moisture-reaches-washington-and.html

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  2. a bit early? isn't the first week of August the dryest time of year?, I suspect the rest of August will be blazing hot and dry if this system pans out or even if it doesn't pan out for that matter.

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  3. Um...so to put this in boxing terms...Western Washington will be hit by a strong jab...but Eastern Washington will be hit by a Joe Frasier style of left hook!...it looks like Puget Sound will survive this round...but E. Wash?...a TKO is likely!

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  4. Still a little confused as to when W. Washington will be getting hit...you mean like maybe 5-6 days from now?

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  5. Hmm...was hoping to stain my deck this weekend (in Ballard) but need 48 hours dry time after completing. Cliff - this latest blog post has me concerned about getting 48 hours of dry time. Thoughts based on what you are seeing?

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    Replies
    1. Your deck will be fine this weekend! But next weekend is a different story!

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  6. GLAD to hear of rain coming,but why aren't other forecasters saying such???

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  7. Attending a wedding next weekend - will the system clear through in time!? This is a nightmare.

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  8. Confused…rain this weekend or next?

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  9. Cliff, any recommendations for ceiling level forecasts (24-hours max)? I love hiking, but often have to change plans depending on cloud height. I usually just wing it by looking out my window in the morning. Low (< 4k') or high (> 10k') is usually fine. For example, tomorrow shows cloudy in the cascades. But there's very limited information on the type of cloudiness.

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  10. We need this rain so, so bad.

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  11. from the Bootleg Fire update today:

    " Despite the recent rain, fire activity picked up yesterday. Fire Behavior Specialist Chris Moore commented on how unusual it is to see fire flare ups so quickly after a wetting rain. “As we move out of normal climatological range, previous experience is less relevant,” said Moore. “The rain that we got will not put the fire out. Spotting will become more of an issue as fuels dry out again.” Incident Commander Norm McDonald reinforced this caution stating that we need “a recalibration of where we are. There isn’t a ‘normal’ anymore. We need to be
    prepared for anything.” "

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  12. Fingers crossed on my end, science on our end. Bring it on.

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  13. Damn, we have a trip to WA Coast planned next weekend

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  14. Will this moisture get down to Central Oregon or stay up north? Thank you!

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  15. If I recall correctly, five standard deviations corresponds to a probability of one in 3 million, at least for gaussian distributed variables. But rainfall is probably not gaussian distributed.

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  16. Cliff. What does this mean for Sequim,the Blue Hole?

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  17. Any update? Many of us enjoy and appreciate your posts...Thanks for doing what you do! On a random note, any chance you can put a confidence rating for your models?

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Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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