Sunday, March 27, 2016

Huge Ridge and Extraordinary Weather Ahead

A front went through last night, behind which cool, unstable air flooded into the region (see high-res visible satellite below).  How can one tell?  Those popcorn-looking clouds over the Pacific are associated with convection, which in turn is produced by an unstable atmosphere with cold air going over relatively warm water.

As typical in spring, the passage of a front and the veering of winds towards the west along the coast, resulted in the development of a strong Puget Sound convergence zone, with intense precipitation over central and northern Puget Sound (see image).  In contrast, there is bright sun and clear skies to the lee of the mountains of Vancouver Island and the Olympics.  The advantage of the can choose your weather.

Here are shots from the Space Needle Cam at 9:20 AM. Heavy rain to the north and sun to the south.  (North, West, South).  Classic.  Pick your weather.

But the big weather story this week is the development of a huge ridge of high pressure over the eastern Pacific.  Let me show you the upper level (500 hPa) forecasts of the UW WRF modeling system.

First on Tuesday at 5 AM.   Wow.   Mega ridge with troughs on its flank.  This is called an omega block and is very stable.

 Thursday at 4AM, the ridge is still strong and has moved towards the coast.

Friday morning, still there.

 Now, this is one model run...can we trust it?  The way to tell is to look at ensembles of many forecast runs.  One application of ensembles is to look at the ensemble mean, which typically is more skillful than any individual member.  The average height anomaly at 500 hPa (the average difference of the ensemble members from normal)  for Wednesday afternoon shows a huge positive anomaly...much higher than normal, over the eastern Pacific.

Another way is look at spaghetti maps, in which height lines from all the ensemble members are plotted.  Here is such  map for Wednesday at 5 PM. Virtually all the members are going for the ridge.  This prediction looks solid.

The implications of this predicted eastern Pacific ridge is profound, with warm temperatures and sunny skies.   Here is the latest forecasts from  Mid to upper 60s for much of the upcoming week.  Enjoy.


John said...

Note that the greatest height anomalies are over southeast Alaska.They are expecting record or near record max temps Thursday and Friday-- max temps near or exceeding 60!

richard583 said...

Good to see people using the term "popcorn" more, as with where you have with your if more, popcorn looking, clouds. (I just say "popcorn".). It's a good one I feel, descriptive where and—if of course—along with the mention of both cold air and instability.

Dennis The Tiger said...

Cliff, I'll be frank, I'll be surprised if I see it get near 70 on, of all days, April 1. =)

Matt Crissman said...

Hoping this early strong ridge is not a sign that last summer is going to rear it's ugly head again this year in Seattle.

Unknown said...

And, of course, this is the same stretch of time we'll be on vacation on the Caribbean. Oh, irony.

tracksdc89 said...

Doesn't it always work out that way? Enjoy your trip, nonetheless!

tracksdc89 said...

Matt raises an excellent point and I share his concern. This would be the ideal time to address such concerns, as we are about to have a brief "summer preview" this week.

Although so far this year the weather has varied greatly with that of last year (temps and precip), all it with would need is another very tenacious blocking pattern to settle in early (as last year's negligible April, May, June, and July precip testify) in order to doom us to the same fate.

Currently having a considerable precip surplus is encouraging, although just like a human drinking a week's worth of water in one day prior to abstaining for a week would be just as dead at the end of the week as someone who drank only one day's worth of water before the same deprivation.

Despite our precip numbers looking great, another 4 month hiatus on precip would be even more problematic seeing how drought damage is cumulative.

We need a summer with occasional rain, not another lengthy rain-free stretch (but let's be clear: in no way am I rooting for a cold and wet summer!)

Are there any indicators at this point of a similar pattern to last year's developing? (Sorry for this very long-winded entry! )

Cliff Mass said...

There is no doom or same fate ahead. We will be much better off than last year no matter what happens. Why? Because we have an excellent snowpack right not and last year hardly anything. AND are reservoirs are in great shape. There is no reason to expect a persistent ridge pattern like last year..... cliff

tracksdc89 said...

Thank you Cliff! Great news to start off this great week!

sunsnow12 said...

Cliff – can you please consider a blog post that discusses 1) our reservoir/watershed system, how large it is, and why it was developed; 2) the fact that snowpack is gone by June 30th that feed SPU reservoirs (ie there is no snowpack runoff feeding our water supply in July, August, or September, except in the most extreme snowpack years and even that would be gone in July); 3) that the highest elevation (Meadow Mountain) in our Cedar watershed is only 5400 feet, and that what matters, like last year, is that our reservoirs are full (with rain or snowmelt) by July 1; 4) that we live in a temperate climate where we receive about 12% of our precip in June, July, August and September combined, and the other 88% from October-May (mostly Nov, Dec, Jan and Feb); 5) that we typically go long periods (weeks at a time) with dry weather in the summer (July and August average under an inch of rain per month), and what would actually be abnormal, for our summers, would be any substantial rainfall, 6) that we ended last water year (Sept 30th) with 20 billion gallons left over – or about 170 days worth of water at normal usage with zero replenishment. And then also - how quickly those reservoirs fill back up with water (ie November precip added an additional 20 billion gallons to put us at 80+% of total capacity - before December's rain - in 2015).

Hope you find time to do it... the bluest skies you've ever seen are in Seattle! Mostly June, July, August and September, but still, they're blue and beautiful!

richard583 said...

Regarding the idea of some type of "death" or "stronger" ridge type regime setting in later this summer, somehow indicated by,
connected in some way possibly to this early Omega. (Hoped against above, part of "Matt Crissman's" comments.) .. I'd say, if more basically, that amplification certainly isn't always connected / associated with duration.

Gpacharlie said...

Omega block - yahoo... Going to go buy an A/C unit before they sell out.

Jonathan Ursin said...


Bob said...

Omega block... Zombie Blob?? Must cook brains... Better row out there and stir the north Pacific!

Mark said...

ooops, quoted an old Steve Gregory blog. I should have looked at the date. Rain in SoCal after March 31 is unusual.

AnneScott said...

With El Nino weakening and La Nina conditions a possibility in the central Pacific I would highly doubt we would see a repeat of last Spring and first half of Summer. But if you look at the spring temps and precip during the last 2 very strong el ninos (1992 and 1998, warm and dry especially late April and May both years) than this is quite normal.