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.

Not All Daily Temperature Records Are the Same

Yesterday, the temperature at SeaTac Airport rose to 89F,  beating the all-time daily record for the date (86F)!

Today, even if the temperature is the same today, it won't break any records.

How could this be?

It turns out that not all records are equal.

Let me explain.

Below is a plot of observed temperatures (blue bars), average temperature range (brown band),  and record highs (red) and lows (blue) for June at Boeing Field in Seattle.

Look carefully at the record highs.   A large variation of record highs in June from 81F to 104F!  Generally around 90F.   

So why the variability?    

It turns out that to get the really high temperatures in western Washington, the atmosphere needs to organize itself in a very specific way, generally with a strong upper-level ridge and offshore-directed flow at low levels.

And on some days, by the luck of the draw, the atmosphere gets the right setup for maximal heat. After many years, the needed flow pattern occurs, and the temperature climbs to record levels.

Global warming plays very little role in these records---the key is getting the right atmospheric flow situation.

Would you like me to prove this to you?

Here is a plot of the highest maximum temperature each year between June 7 and June 21 since 1950 at Olympic Airport (a less urbanized location than SeaTac).   No apparent upward trend.

Turning back to SeaTac, below is a plot of the highest temperature on June 14th at that location (below).  

2025 was the warmest year on record for that date.  But note!  There is no trend in the record temperatures for that date over the entire period of record.

In fact, the highest temperatures on June 14th are trending down!  (brown line).  

So the global warming claims for the origin of such records should be taken with a large grain of salt.

Meteor Clouds

Some of the greatest treats of June are the relatively rare but stunningly beautiful noctilucent clouds that form very high in the Earth's atmosphere during this time of the year.

Thursday night, there was quite a show, as illustrated by the pictures below.

Picture courtesy of SkunkBay Weather (from central Puget Sound)

Eastern WA

Noctilucent clouds form high in the atmosphere, about 50 miles above the surface, when water vapor condenses on meteor dust, producing small ice crystals that make up the clouds.

Such clouds are only apparent from late May to early August within a relatively narrow band of latitudes (roughly 50 to 70 degrees)--leaving Washington State on the southern edge of the viewable domain.

Why such limitations, you ask?

First, the formation of such ice requires very, very cold temperatures and the upper atmosphere (called the mesosphere) is coldest during late spring and summer.

Second, the clouds are best illuminated by the sun located below the horizon, and summer provides the optimum sun angle.

Short Heatwave Followed by Normal Temperatures and Precipitation

It is now clear that our region will experience a short-period heatwave on Sunday and Monday, with the highs in Seattle reaching near 90F and eastern Washington climbing into the upper 90s.

This is after a relatively cool start to June and the expectation of normal temperatures the rest of the month.

A plot of the temperature at SeaTac, with observations (blue bars), and record highs (red) and lows (light blue) shown, indicates that we have generally been cooler than normal this month.  Record highs on any day are generally around 90F.

The crazy record high in 2021 is evident at the end of the month.  

To put this month in a better long-term perspective, I have plotted the average maximum temperatures at Seattle from 1-10 June for the past 50 years (a trend line is also plotted).

We have started this month, a bit below normal.  But you will notice a small upward trend (brown line) since the 1970s.   That could well be the influence of human-caused warming produced by increasing greenhouse gases.

Now turning to the forecasts, below is the latest National Weather Service forecast for Seattle. Friday and Saturday will be comfortable, but then temperatures increase, reaching 90F on Monday, before declining to normal next week.

Eastern WA will also warm, with the Tri-Cities climbing into the upper 90s before cooling into the mid-90s.   These are not exceptional temperatures in the central Columbia Basin.

 After this warming period, substation precipitation is predicted to return to the region, as shown by the total accumulation through thourgh June 25th (below).    Particularly heavy in British Columbia, which is very good for the Columbia River.  Very favorable for our power generation and irrigation needs.

Recent substantial rain has contributed to Yakima River storage, which is almost exactly at normal levels.   Very good for irrigation in the Yakima Valley this summer.

Meteorological Roller Coaster

June is an interesting weather month in the Northwest.

The sun is very strong, so with the right conditions, temperatures can zoom up to extremes, such as the stunning heatwave of late June 2021 (108°F in Seattle).  On the other hand, with moist onshore flow, our temperatures struggle to rise into the 60s.  The Pacific Ocean off our coast is only around 50°F.

During the next week or so, we will experience a prime case of a meteorological roller coaster.

Consider the latest forecast for Seattle from the European Center model (below).

A high today (Monday) in the upper 50s, with a slow climb into the 70s by Saturday.   Then a sprint to around 90 degrees, followed by a nearly 20F decline next Wednesday.  This is followed by a rise into the upper 80s, with a huge cooling in the subsequent days.

My head is spinning!

The potential to get warm in June is illustrated in the climatological highs (red) and lows (light blue) below for Seattle, with the temperatures this year shown by the dark blue bars (brown indicates the average range).

Once we get past mid-May, high temperature records reach the 90s.  Once in June, low temperatures remain above 40F.

But to get the heat, as will occur in a week, requires offshore-directed flow that pushes the cool, marine influence offshore.  Such easterly (from the east) winds result in downslope flow on the western sides of the Cascades.

Downslope flow warms rapidly by compression as air traverses from low pressure aloft to high pressure near the surface.  

Today (Monday), a very wet weather system is moving in (see satellite image), with clouds, precipitation, and very cool onshore flow.

But in a week, high pressure will build inland, producing offshore-directed winds and profound warming.  

Consider the forecast for Sunday morning for sea level pressure (solid lines), low-level winds (the wind barbs), and low-level temperature (shading), shown below.

A transient high has moved east of us, producing winds from the east to the west. The air warms as it sinks on the western side of the Cascades (pink colors).  Warm air is less dense than cold air, which results in lower pressure over western Oregon and Washington (called a trough in the weather business). 

This situation won't last long, because the high pressure to the east will move away.   As it does so and the winds from the east weaken, the winds from off the ocean will surge in, producing rapid cooling--something called an onshore or marine surge.  

To illustrate, the same map for Wednesday morning is shown below. The reds on the west are replaced by cool greens.  You may need a sweater again.

As discussed in a previous blog, the "locked up" pattern of the past winter has been replaced by one in which pressure systems progressively move through the region.  Thus, we will experience a range of weather conditions, from warm and dry to cold and wet, and meteorologists will have less boredom to contend with.