Welcome to Summer 2021, or at least the meteorological definition.  There’s a longstanding confusion in the United States, as to which calendar format we should use for  defining seasons.  Several decades ago it was far more common to see the “astronomical” summer used in practice by media and popular culture.  That begins near June 21 in the Northern Hemisphere, and ends around September 22.  However in recent years, the meteorological summer- June 1 to August 31 -is gaining more acceptance as an “official” standard to go by.

I think this is going to be a far happier summer than last (of course!).  With the Covid pandemic gradually subsiding and social life reopening, I can sense the mood.  Most importantly for me…live music is coming back!  Familiar faces are popping up at gigs again.  On Sunday there was a show by BrandonLee Cierley and his band – and as a proud student of his, I knew this was the place to be!

Obviously many of us are gearing up for fun times this summer.  But as weather nerds, what kind of conditions can we expect?

THE OUTLOOK

These maps were published on May 20th.  They’re not good for day-to-day weather patterns, only the general trend.  Nonetheless there is a strong signal that June-August will end up hot across most of the Western U.S. :

By the way, we’re using the new climatology normals now (1991-2020).  Those decades were significantly warmer than the 1981-2010 normals.  So this would imply a summer that is hotter than most summers since 1991.  We can expect more maps to look like this in the future, by the way. As the planet continues to steadily get warmer, even 30-year norms won’t be a good indicator of current conditions.

There’s bad news on the precipitation front…drier than normal is expected to persist across most of the West this summer:

Obviously our summers on the West Coast are dry anyway.  So a drier-than-normal summer in Seattle or Portland doesn’t have nearly as much bearing on drought as an unusually dry winter or spring does.  That said, a hot summer with low humidity is still a lot worse for wildfires, than a cool summer with lots of marine clouds.  This is doubly true if hot east winds develop at the same time.

On the other hand, the Rockies and even far eastern Oregon, have a more pronounced summer monsoon season. Missing out on normal summer rain there, can have a bigger impact on overall drought conditions. (Fire is more complicated, since it is also impacted by the frequency of lightning events!)

THE DROUGHT 

As I mentioned above, summer conditions don’t affect PNW drought trends very much because it’s the core of our dry season anyway.  (A very wet June can be a partial exception to that rule.)  A record-dry spring, however, can have a BIG impact. Portland Airport just “obliterated” its old dry record for the March-May season:  only 2.52″, compared to 4.31″ in 1994.  The 30-year normal for spring precip is 9.37″.  Basically our spring was as dry as a normal summer:  March was like a normal June, and April and May were like July-August. 

Given that we had a pretty normal winter for rainfall, it took a while for the extremely dry spring to take its toll on our soil and groundwater. But take its toll it did:  notice how drought conditions over northwestern and north-central Oregon exploded in the 8-week period from April 6 to June 1:

Unless we get a miracle (i.e. 3-4″ of rain in Portland between now and mid-July), these drought conditions are now pretty much “locked in” for the summer. That means a very rough season for farmers, fishers, and various forms of outdoor recreation.  There are going to be a lot of brown lawns in our cities and towns this year!

Here are current drought maps for Washington and the entire West:

FIRE THOUGHTS 

Many people are wondering if this year will be as bad as last year for wildfires.  My immediate thought is:  Probably not, unless we get brazenly unlucky for the second year in a row.  But what do I mean by that?

Last year’s Labor Day megafires were triggered by a historic pattern:  an exceptionally strong and dry east wind coming at what is normally the driest time of year, fuel-wise.  Our worst wildfires have often occurred in early fall under this same basic pattern.  The Yacolt Burn of 1902 was conflagrated by a strong September east wind, to name an old example. Even the Eagle Creek Fire of 2017 had hot east wind at its back.

Why early fall?  Because that’s when cold Canadian airmasses begin to develop, along with the dry high pressure they tend to bring when they dive southward.  Paradoxically, these early cold airmasses in the Rockies make for bad fire weather in our region, due to the strong and dry east wind they tend to generate.  Later in the fall, the ground is typically too cool and moist for even a strong east wind to cause trouble.

Last year’s east wind in early September, was roughly a 50-year occurrence…so it’s pretty unlikely to repeat itself this year. But there are already troubling signs this will nonetheless be a tough fire season:  There was a wildfire last week in the Columbia River Gorge west of The Dalles. Here is a tweet of some footage, courtesy of Kristi Martian.

https://twitter.com/gorgewx/status/1400209881064374274?s=19

Most of our fires this season will probably be started by “normal” causes:  lightning, fireworks, vehicles, and the like.  But our unusually dry landscape will increase the likelihood that any one of these sparks will trigger a major wildfire.

We have no idea just how many lightning bolts there will be, or how out-of-hand the fireworks will get this year (hopefully not as bad as last year in Portland! 😵).  Nor do we know if those scenarios, if they happen, will occur under hot/dry or cool/humid conditions.  Based both on drought and on the expectation of a hot summer, I think there’s a high probability of severe fire conditions at some point this season. But we could always avoid serious trouble if we get really lucky.

Probably the most likely “unlucky” scenario?  A large cluster of T-storms with dry lightning, could start a lot of fires in a short time.  (That’s what happened in northern California late last summer!)

 

….So it’s still early June, and as I mentioned above, we CAN still get soaking rain at this time of year.  It wouldn’t eliminate our drought and fire problems, but it could dampen down the danger for the first few weeks of the season.

We have some rain coming in tomorrow Friday.  A classic June cold front arrives near daybreak tomorrow, as per the WRF-GFS:

Normally this cold front, and the associated trough of low pressure, would sweep through the region quickly. But in this case the trough will just continue to deepen offshore. By Saturday through Monday we are in humid SSW flow.  That means high dewpoints (i.e. 60 degrees) and in this case, a good chance at more showers and thunderstorms over the weekend. Here’s the image for 5pm Sunday, notice all the shower cells developing over the Oregon Cascades and points immediately east:

By late Monday most of the precip should be pushing off to the north.  We dry out again next week. Rainfall totals look to be near an inch for PDX, and over 2″ in the high Cascades.  But don’t take rainfall forecasts too literally; there’s a huge margin of error lurking in the details!

WeatherTogether blogger Charlie Phillips wrote a more extensive blog two evenings ago, on this weekend’s rain chances.  I will simply say that while rain is good, lightning could be really bad if it strikes in an area that’s still mostly dry (such as central and eastern Oregon and Washington).  So depending on details, this weekend could either represent a reprieve from the worst fire danger…or it could be the opening salvo in a rugged, smoky season.

Either way, have fun and be safe this summer! -Karl