Cooler Than Normal Water Off the Northwest Coast

One of the reasons Northwest weather is so temperate in summer is the cool coastal waters off our coast.

And this year, we start the summer with surface waters cooler than normal.

This is illustrated by the sea surface temperature anomalies (differences) from normal (below), with blue indicating cooler than normal water.

Below is a map of sea surface temperatures off the U.S. West Coast (°C).   The purple and blue colors indicate the coldest temperatures.   You will need a sweater to enjoy a coastal stroll!

Why such cold water along the coast? 

One reason is the upwelling of cold water from below, as illustrated by the figure below. Such upwelling is forced by northerly (from the north) winds along the West Coast.

Importantly, these northerly winds have been stronger than normal for the past month.

Why? 

Because of stronger-than-normal surface high pressure offshore of the northwest.  This is demonstrated by the figure below, which shows the sea-level pressure anomaly (difference) from normal over the past month.

The red area indicates a much higher-than-normal high-pressure area offshore.

Since winds move clockwise around high-pressure areas in the Northern Hemisphere, this implies enhanced northerly flow along the coast, something shown explicitly in the figure below (which shows the wind differences from normal of the past month).

With this persistent pressure/wind pattern in place, the current 5-day forecasts are for colder than normal conditions over western Washington, Oregon, and British Columbia (blue and green indicate colder than normal conditions)

Keep your sweaters handy!

Wind and Fireworks Brings A Fast-Growing Wildfire Near Lake Chelan

 The  Chelan Hills fire, reported to have been started by some irresponsible fireworks Saturday morning, has now spread to over 10,000 acres (see map below).

A high-resolution visible satellite image this morning shows the burnt area (dark color), and the satellite imagery shows some still-active fires (red dots).  Smoke from  another (smaller) fire is apparent to the southwest.

The fire started in grass and range vegetation, not forest.  

Importantly, this vegetation was NOT unusually dry, as shown in the figure below, which provides 100-h fuel moisture levels on the eastern slopes of the Cascades.  Red is observed moisture level, and the shading shows the normal range.  

Current moisture levels were above normal.

So "climate change" can not be blamed.

What can be blamed was strong winds.  

Winds that were skillfully forecast by the UW WRF modeling system and the NOAA models.  To illustrate, below is the wind forecast for Saturday afteroon be the UW WRF weather model....strong winds were predicted around Chelan!

Below are the strongest observed winds yesterday around the fire area.  A 36 mph gust was observed near the fire start.

Winds at this location really revved up during the afternoon and early evening (see below).

At the same time, relative humidity plummeted to less than 20%--the result of drying of air moving downslope on the eastern side of the Cascades.

There is reason that wildfire starts are maximized on July 4th.  

The ignitions are there, the grasses/range vegetation are dry enough to burn, and it is early enough in the summer so that strong onshore flow produces powerful winds.

How Much Has Global Warming Changed July 4th Temperatures Over Washington State?

Walking my dog yesterday, I ran into a neighbor who asked whether July 4th temperatures in our area had changed much under global warming. 

I promised to run the numbers... and here are the results.  

Be prepared to be surprised 😀.

Starting at Olympia, on the western side of the state, there is almost no trend in July 4 daily average temperatures since the 1940s! (The purple line is the linear trend).

What about the highest temperatures each year on July 4 in Olympia?   

No trend!  

OK, now let's check Yakima in eastern Washington! 

The July 4 average temperature trend is slightly upward (a little less than 2 F over 75 years).

The trend in the maximum temperatures at Yakima is similar.  Modest upward increase.

And then there is Spokane, over the northeast side of Washington (below).  Very little trend in average July 4th temperatures or in the highest temperatures on that date.

What about precipitation on July 4th in Olympia?  As shown below, there is little evidence of a long-term trend.

Anyway,  a big yawn is appropriate for the July 4 trends in temperature over Washington State.

The planet is slowly warming for sure, but the temperature trends in Washington State are very, very modest.

But you might get a different answer if you relied on AI.  

I asked Google's AI to create a graphic summarizing the July 4 temperature trend over Washington.

It created the graphic below, with a dramatic upward trend over Washington from 26F to 80°F since 1990 (below).  Was it really below freezing in July in 1990?

Total nonsense.  

A Perfect July 4th Weekend in the Pacific Northwest

With an extreme heat watch over much of the central and northeast U.S., including temperatures reaching near 100 F (see below), it is good to know that the weather over the Northwest will be near perfect over the holiday weekend.

Temperatures will rise into the mid-70s in Seattle on Friday through Sunday, while temperatures in eastern Washington will reach about 90F.  

A forecast map of surface air temperatures around 8 PM on Saturday, July 4,  shows the mild temperatures in western Washington, with reasonable warmth in the Columbia Basin.     Cool in the mountains.

No worries about precipitation on July 4th, as illustrated by 3-h precipitation totals ending 11 PM that day (below).

Obscuring clouds on Independence Day?    Here is the cloud prediction for 5 PM Saturday.   Mostly clearly, except for high terrain in the Olympics.

To make things even better, the cool/wet conditions this week have made regional fuels less flammable, reducing fire risk this weekend (when all kinds of crazy fireworks activity will occur).   See the predicted ERC and Fuel Moisture values below.  There are no reds (serious risk) and only some marginal values (orange).

  But please be careful.  

Wind and Wildfire

When it comes to Northwest wildfires, many only consider precipitation and temperature.

But for most Northwest wildfires during the summer, another element is more important:  strong winds.

Recent grass and range fires in eastern Washington are prime examples of their "windy" origin.

For example, yesterday, there was a grass fire near Winthrop (see below).  Strong winds were crucial.

Another grass/range fire (the Peterson fire) surged rapidly this week in Klickitat County (below).  Strong winds again.

A few weeks ago, large range fires (e.g., Juniper Dune, Tule Rd) were also forced by strong winds.

In a map of recent eastern Washington wildfires, virtually all were associated with strong winds (graphic courtesy of the Washington State Department of Ecology).

More than climate change warming, strong winds are the essential ingredient for the large grass/range fires in the region.  

In fact, cool/wet spring weather can worsen wildfires in our region, since wet/cool springs enhance the amount of vegetation, which inevitably dries out during our typically arid summers.  That means more fuel.

This week was a great example of strong winds, associated with cooler temperatures, leading to rapidly growing range/grass fires.

Consider the winds at Ellensburg from June 22 to today (below).  Sustained winds are shown in blue and gusts with black dots.

A large acceleration of the winds started on June 26, with some gusts reaching over 50 mph!

As the winds increased, temperatures greatly COOLED at this location (see below).

Want to be impressed with how strong the winds have been this week, east of the Cascade crest?   

Below are the maximum gusts yesterday (Sunday) over eastern Washington.   

Wow.  Many exceed 50 mph, and some reach over 60 mph.

Why are there strong, fire-supporting winds when temperatures cool?

When cool air moves into the region from the west, it causes pressure to rise west of the crest, since cold air is denser and heavier.  That causes low-level pressure to rise.   Even if some cool air gets over the Cascades, the depth of the cool air is greater west of the crest, allowing the pressure to rise more to the west.

To illustrate, there is a sea level pressure analysis (solid lines), sustained surface winds (wind barbs), and low-level temperatures (color shading_ at 5 PM Wednesday.   Cooler temperatures to the west and a strong pressure difference over the Cascades.  

A day later,  eastern Washington had cooled, and much stronger winds had spread over the Inland Empire.

This weekend, temperatures will warm, and the winds along the eastern slopes of the Cascades should weaken.  

A Cool/Wet Start of Summer

The forecasts for the next week or so are definitive:   we are going to start the summer quite cool and wet.

And the implications for both wildfires, water resources, and agriculture are quite positive.

Let me begin with temperature, showing you the temperature anomalies from normal for the next 15 days from the most skillful system in the world (the AI forecast of the European Center). 

Blue indicates below normal (up to 5 F colder than normal), and green indicates even colder anomalies.

For the next five days, the whole region is cold, with some areas of Oregon over 10F colder than normal.  

The following five days (through July 2) are colder than normal over the entire region, with British Columbia being the most frigid.

Even colder for the following five days (through July 7).

In Seattle, my colleagues at the National Weather Service don't predict high temperatures will reach 70F during the next week (below).

Importantly, no big heatwave in eastern Washington, so crops will not be stressed.  To show this, here are the predicted temperatures at Yakima.  Very temperate for the dry side.

And there will be precipitation at times through July 8. 

Substantial amounts in the Cascades (up to around 2-3 inches) and large totals in the Rockies (see below).  Importantly, even eastern Washington will get some light rain.

Want more good news?     

This kind of cool pattern is very favorable for wind energy, as it is associated with substantial westerly winds descending the eastern slopes of the Cascades.   To demonstrate this, below are the latest wind generation numbers from Bonneville (below)

Wind energy generation (the green line) surged upwards as temperatures cooled.  Furthermore, energy use (red line) has dropped substantially as air conditioning demands have declined with the cooler temperatures.

Thunderstorms and a Winter-Like System Approaches the Pacific Northwest

A wet, winter-like frontal system is now approaching the Northwest and will arrive on Friday, but before I discuss it, let's consider the substantial thunderstorm activity that struck the regional mountains on Wednesday.

The weather radar image around 2 PM Wednesday showed a strong thunderstorm over the northeast Olympics and a line of convective showers over the eastern slopes of the Cascades.

The Seattle Space Needle panocam showed the extensive scale of the Olympic Peninsula thunderstorm:

And the Space Needle cam also indicated a line of storms over and east of the Cascades.

The Wednesday thunderstorms were associated with hundreds of lightning strokes, as illustrated by a one-hour sample during the mid-afternoon on Wednesday:

Why is there so much lighting on Wednesday afternoon?    

The air above us was unusually unstable, meaning that a rising parcel of air would tend to accelerate upward if lifted.   A measure of such potential instability is called CAPE (Convective Available Potential Energy), and values of CAPE were unusually high over the region (see plot below).

High for the Northwest, but the folks in the Midwest would laugh.

Convection tends to release at the surface warms, but yesterday the process was aided by increasing westerly winds (from the west), which provided strong upslope flow over the high terrain.  It helps to give the air a kick upwards to get the instability going.

Finally, a wet, winter-like system is now approaching our region, as illustrated by the latest infrared satellite image (below).  Looks like winter!

The total forecast precipitation over the region through Sunday morning is substantial (see below), and should both moisten the surface, add to the water supply, and reduce wildfire potential.