Tuesday, June 4, 2019

Cool, Cloudy, and Wet Period Ahead

Cooler, wet weather is ahead, something that the models picked up on over a week ago.  And this intrusion of clouds and rain is highly welcome in many ways--for agriculture, home gardens, and to reduce fire danger, particularly in British Columbia and northeast Washington.

The spigot will turn on slowly starting late Wednesday, with Friday being the wettest and coolest day. 

Let me begin by showing you the forecast accumulated precipitation through 5 PM Saturday from the UW WRF model (below).  Precipitation will occurr over the entire region, with the exception of the Yakima area in the rainshadow of the Cascades.  As much as 1-2 inches in the Washington Cascades, but what is really impressive are the totals north of the border.  The values in Alberta are very large (2-5 inches), which should knock down the fires in Alberta.   Rain in British Columbia is also important, since last year the BC fires were a major source of high-level smoke in the Northwest.


 A closer-in view of the accumulated precipitation through 5 PM Saturday using the European Center model (graphics by WeatherBell Inc.) predicts 1-1.5 inches in the WA Cascades and appreciable amounts over most of western WA, which would lessen the dry condition a notch, particularly over SW Washington.

Why this wet bounty from the sky?   Its origin is the approach of a relatively deep trough for this time of the year over the region.

Let me illustrate this by presenting a series of upper level (500 hPa, about 18,000 ft above sea level) charts.  These charts show the height of that pressure surface above sea level, but you can think of them as pressure at roughly 18,000 ft.  Winds are parallel to the lines and are stronger when the lines are closer together.

At 10 AM today, there will be  strong southwesterly flow over our region and a trough of low pressure/heights (the "L") offshore.  An approaching trough will bring upward motion, clouds, and precipitation.


By 5 PM Wednesday, the trough is closer, which will bring increasing chances of clouds and showers.


By 5 PM Thursday the trough has deepened over the West Coast and extended down to California.  Yes, those poor, sodden California could get more rain.   And western Oregon will definitely get some.


And by late Friday, the trough has pushed right over us.


So enjoy today-- there will be plenty of sun after the low clouds burn off.   Tomorrow, clouds will start streaming in aloft, and the chances of shows will increase.  And don't be shocked by the occurrence of a thunderstorm on Friday--the models are suggesting the possibility of that.  Warmer and drier conditions should be expected by Sunday-- so plan to use that day for outdoor activities.

Finally, lets look back on the spring so far here in Seattle (last 12 weeks).  Temperatures (red lines below) were normal, or cooler than normal, in April, but generally warmer than normal in May.  My tomatoes are doing very well.  The huge temperature spike in early May really sticks out.
Precipitation?   We had a very wet period in early April, but minimal rain in May, leaving us about 2.5 inches below normal for the period.    We should catch up a bit during the next few days.

15 comments:

wxman said...


I think what really sticks out in the temperature graph is how few were the days with below normal minimum temperatures, even during the cool spell in April.
Jim Holcomb

Sharon said...

Cliff,

I welcome the rain and especially enjoy knowing when to expect it. It's a gift for the garden this time of year. Hopefully, summer crops will really flourish after this period. I have some new dahlias I want to see in full bloom.

I'm so ready for summer's long days, relaxed schedules, and day trips.

John K. said...

"I'm so ready for summer's long days" Sigh.. not me. Summer is hot, muggy, noisy, stressful, and uncomfortable. I'm already looking forward to the cool, quiet days of autumn.

Placeholder said...

So much for Inslee's phony "drought emergency."

Sulla said...

I'm right with there with you John!
I enjoyed summer's growing up, but it seems overly hot and now smokey conditions have taken the fun out of summer. I'm hoping for extra June gloom stretching into the 4th of July. And then to NOT have us bake and smoke in August for the 3rd summer in a row. September has me doing a happy dance knowing that's the last month we generally get any uncomfortable heat before Fall energetically shows Summer the door. :)

Snape said...

From Mark Nelson’s weather blog (Portland):

“You may remember the first 10 days of March were very chilly due to leftover snow cover over much of the Pacific Northwest. But then April and May were significantly warmer than average. May 2019 and 2018 rank as #4 and #2 warmest on record! The result = Spring 2019 was #15 warmest out of 80 springs.”

May, 2018 was the warmest on record for Seattle, but I’m not sure about 2019. “Climate at a Glance” is having a problem right now.

Thecatguy93 said...

It baffles me how many people complain about the "uncomfortable heat" around here. Are you kidding me? What, does it get above 90 about two days a year? There isn't a cooler place you could live in the country without being in Alaska. Try having some real problems, we have it very easy here in terms of weather, relative to the rest of the country. Find something that actually matters to complain about. Something people actually have control over, perhaps? There's nothing anyone can do about the weather, complaining is a waste of time. Deal with it, learn to appreciate it, or move. Pretty simple.

Ansel said...

Well, if you like to swim outdoors, some 80-ish weather is needed to warm the lakes enough so you can do so without getting hypothermia. And anyone who thinks our summers are muggy should spend a summer on the east coast. Our humidity level is about right to me- some moisture is good for your skin (and the garden).

But I certainly hope we don't get the smoke.

Scott K. said...

Is there credence in the idea of more rain in eastern WA means more vegetation growth, meaning fires can actually spread easier?

We get enough rain to cause lots of plants to grow, then it goes dry again, but the plants are now burnable fuel just sitting there, instead of the usual sand/dirt that would otherwise be in their place.

It seems like rain is a good short-term solution to keeping the fires away, but might make fires more intense in the longterm.

wynneforplants said...

My garden and spirits definitely prefer 60 temps and rain (how about 1/2-1" every week?). I work outside a lot, and hot summer temps, eg >75? are not good for working, only for lying about in the shade drinking whatever. So I'll keep hoping for more of what we have now, thank you.

(and poo to any ANONYMOUS poster -- hey, Cliff, your promise of not allowing anonymous comments clearly is objectively untrue :( -- who keep trying to force weather discussions here to political hoo-ha, not to mention boringly repetitious)

Shorty said...

We have relatively little mugginess compared to noncoastal states. Don’t ask me how I know. The pacNW has premium summer weather

Anthony Effinger said...

Forecast shows 90s in Portland next week. Looking forward to the spin on that one.

Eric Blair said...

Mark Nelson's blog also said that the trend over the past 50 years is for wetter Springs. He also added that the underlying reasons for the temp variatons is inconclusive. Please stop editing sources to shoehorn your own biased agenda in the future.

Snape said...

@Eric
“Mark Nelson's blog also said that the trend over the past 50 years is for wetter Springs.”

Yes, I’ve mentioned on several occasions that in many areas of the Northwest, springs have been getting wetter and summers drier. That’s an ominous trend WRT wildfires. Portland is no exception. Since 1950:

March - May: + 0.34”/decade
June - August: - 0.11”/decade

https://www.ncdc.noaa.gov/cag/city/time-series/USW00024229/pcp/3/8/1950-2019?base_prd=true&firstbaseyear=1938&lastbaseyear=2000&trend=true&trend_base=10&firsttrendyear=1950&lasttrendyear=2019

******

“He also added that the underlying reasons for the temp variatons is inconclusive. Please stop editing sources to shoehorn your own biased agenda in the future.”

Just stating the most noteworthy facts from his post, Eric. I certainly wouldn’t draw any conclusions based on one month, one location.

February, BTW, was the third coldest in Portland since 1938. Worth noting, but again, not a big deal by itself. On the other hand if next February is also really cold, or a cooling trend appears, then that might be something worth talking about.



Snape said...

I should point out that going back further, since 1895, precipitation trends in the Northwest for summer months, June - August, are flat.

Washington: + 0.02”
Oregon: + 0.01”
California: 0.0”

https://www.ncdc.noaa.gov/cag/statewide/time-series/4/pcp/3/8/1950-2019?base_prd=true&firstbaseyear=1901&lastbaseyear=2000&trend=true&trend_base=10&firsttrendyear=1895&lasttrendyear=2019

Lots of ups and downs, no clear pattern. Let’s hope the more recent drying trend is just random variation and we see a nice uptick in the coming years!