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.

The "Super" El Nino Will Weaken Super Fast

There is a lot of folk wisdom about the current El Nino situation.

The flame that burns twice as bright burns half as long.

Fast ripe, fast rotten.

Up like a rocket, down like a stick.

The higher you climb, the harder you fall.

The media, such as the Seattle Times, have been breathlessly describing the currently developing El Nino, with many applying the unscientific "super" prefix.   Some have suggested devastating impacts (see below).

The latest forecasts paint a different picture.  

El Nino will develop rapidly this summer/fall but will weaken quickly during the winter.

This rapid decline is important, since the winter is the period with the greatest impact of El Nino on the meteorology of the Northwest.

Let me demonstrate this to you.

The latest forecast of the NOAA CFS model (below) predicts a peak warming of the tropical Pacific in October-November to around 2 °C (major El Nino), followed by a rapid cooling to 1°F (moderate El Nino) by January-February.

Looking at a collection of many forecast models (below) provides a similar picture:  a substantial weakening of El Nino during the winter.

The bottom line of these forecasts is that some of the over-the-top predictions by the media and others regarding a super El Nino causing severe weather impacts may be a bit over the top.

Finally, looking at the current short-period forecasts, it appears that we have a wet/cooler than normal period ahead, as shown by the NOAA predictions below.

The latest UW forecast model predictions for precipitation totals through Sunday morning (below indicate a nice wetting across Washington State.  A lot more precipitation is predicted during the next 10 days.

Short Warm Period Followed by Cool Wet Weather

We are about to warm up into the mid-80s this week in the west and 90s in eastern Washington, followed by a profound cool-down and plenty of precipitation.

Consider the latest predictions for temperature in Seattle and the Tri-Cities below.

Temperatures peak on Wednesday, before dropping off the proverbial cliff by the end of the week. 

Classic for our region, where cool ocean air is always close by.

You can see the predicted regional temperature evolution spatially below.

The forecast high temperatures for today are quite moderate over western Washington (highs in the 70s), while warmer temperatures are found in the Columbia Basin.

But by Tuesday (at 5 PM), the reds (80s) have spread into western Washington.   Still cool along the coast and over NW Washington.

But by Thursday, a radical cooling has occurred in the west, with temperatures only getting into the 60s over the lowlands.  Eastern Washington has also cooled.

The cause of this transition?   The approach of a strong upper level tough of low pressure (see forecast at 500 hPa, about 18,000 ft) below.   Wow.

Are you planning a hike after Thursday?   Bring some rain gear.

To illustrate our soggy future, below are the predicted precipitation totals through Sunday morning.  Yikes.  Several inches in the mountains.  Even eastern Washington gets wet!

The NOAA Extended (6-10 day forecast) is wetter than normal over our region (see below)

The timing of this precipitation, right before our dry season, is superb for providing soil moisture, filling reservoirs, and reducing wildfire threat.

The Current Status of the Most Important Water Source in the Northwest: The Columbia River

When it comes to our summer water supply, nothing is as important as the Columbia River.

It is the largest regional source of water for agriculture.

Its water is the largest source of power in the region.

Its water supports important salmon runs.  

And Columbia River water is used for drinking purposes in some communities.

This year, the water availability of the Columbia River should be very close to normal, with no hint of drought conditions.

Let's start at the water level of Lake Roosevelt behind Grand Coulee Dam on the Columbia River (below).   The blue color indicates this year's level, which is almost exactly at normal levels (red line).

 

Or we can look at the predicted water supply for April through September at Grand Coulee Dam, with the latest predictions on the right side.  The forecast is only slightly below normal (green line).    The water supply on the river looks quite adequate this summer.

The Columbia River is in good shape because precipitation over southern BC was near normal this year, and the snowpack in the Columbia headwaters is near normal (see below)

Also encouraging is the substantial precipitation predicted through July 4  over western Canada (see below).

As I have suggested in earlier blogs, there is little reason to talk about drought over the Pacific Northwest this year.

Grass Fires in Eastern Washington: Strong Winds and Human Ignition

June is the beginning of the grass wildfire season over the lowlands of eastern Washington.

By June, the extensive grass and range vegetation of the Columbia Basin has dried out and "seasoned" sufficiently to burn.  Also in June, strong westerly (from the west) winds can develop as weak Pacific weather systems move through.

Dry range vegetation, strong winds, and an ignition source are the ingredients for a large, fast-spreading fire. 

All of this has happened over the past few days, producing several significant grass and range fires, including the one at Juniper Dunes (13,000 acres!).   

The map below shows some of the recent fires.

Here is a satellite image of the Juniper Dune fire from two days ago.   Pretty impressive looking.

The grass fires are now history, but you can see the burned (brown) areas in today's visible satellite image.

So why the fires?  

The fuel moisture of small dead fuels was under 11% and thus flammable (see below).

Looking at the 100-hr dead fuel moisture (for larger dead debris) over the Columbia Basin (below), shows that fuel moisture (solid red line) dropped below normal with our short heat wave (the gray band shows the normal range of fuel moisture).  

Light dead fuels, such as grasses and small-diameter debris, can dry out within hours under the right conditions.

And then there are the winds resulting from the passage of a weak trough aloft.  To illustrate, here are the gusts yesterday---at several locations they exceeded 50 mph!

The strong winds are critical for the rapid expansion of such prairie fires.

It appears that these fires were initiated by careless humans, which is true of most eastern Washington grass fires.