Substantial Precipitation Will Soon Return to the Pacific Northwest

For those worried about Pacific Northwest drought, I have some news that should give them substantial comfort: substantial rain and snow will return to the Pacific, accompanied by cool temperatures.  

And not a hint of any heatwaves.  In fact, much cooler temperatures are expected.

So get your rain jacket out of the closet, get ready to plant some seeds,  and think about delaying that late-May hike.

Let's start with the best, the European Center model forecast for precipitation over the area (below).

The expected precipitation through Wednesday afternoon starts the wetting process:

By Sunday evening, all the mountains will be thoroughly moistened.  

But there is more!  By the morning of Monday, May 25, the totals are impressive, with some mountain locations exceeding 4 inches.  Even rain in eastern Washington.  This is serious precipitation.

Importantly, temperatures will cool substantially over the next week, so there will be substantial fresh snow in the Cascades (below).   Expect the % of normal snowpack to rise substantially from this late-season snow.

So what is going on?  

With the change in season and the transition from La Niña to El Nino, the upper- level pattern has unlocked, and some strong troughs of low pressure will be moving into the Northwest.  

To illustrate,  below is the forecast upper-level map for Friday morning.  An impressive trough of low pressure (blue colors) will build off our coast.

A week later, ANOTHER strong trough is forecast....winter-like in intensity in a similar position.

Other modeling systems (like the NOAA GFS) are doing similar things.   

Extremely favorable and well-timed for Northwest agriculture and local water resources.

Major Forecast Failure

Weather prediction has become hugely more skillful during the past several decades, but there are still some failure modes.

This week in western Washington, we had a master class in forecast failure due to our local weather nemesis:  low clouds.

On Monday afternoon, the National Weather Service forecast for the high temperature in Seattle on Tuesday was 76F.   For Wednesday afternoon, 72F (see below).

The actual highs?  66 F and 57F.  

HUGE errors on the cold side (10F and 15F!)

Instead of a continued warm period, temperatures were well below normal (see a comparison to climatology below).  The brown color shows the normal range. 

The vaunted UW high-resolution ensemble of many model forecasts at Seattle (below) was highly accurate on Monday, but too cool on Tuesday and Wednesday (yellow dots are observations).

In contrast, forecasts of the National Weather Service and the UW model for the Washington Coast and Eastern Washington were excellent.

So what is going on?   

This event (and others like it) demonstrates a great weakness of most weather prediction systems:   an inability to predict or maintain a cool, shallow cloud layer.

Most models tend to produce too much low-level mixing, which destroys shallow, cold, saturated layers.

Let me show you the proof.  

There are visible satellite images for 2 PM on Tuesday and Wednesday.  Lots of low clouds over the western lowlands.  Clouds associated with cool surface temperatures.

In contrast, the predicted clouds, the UW WRF model, or the National Weather Service GFS models had no low clouds over western Washington.

Several of us are working on this problem, but in the meantime, either the National Weather Service forecasters need to more actively intervene in the forecasts, or we need to more effectively apply statistical corrections during these low-cloud periods.

This is a serious problem for Western Washington since low clouds are quite frequent during late spring and early summer.

June Gloom Comes Early

It is the transition that Northwest residents both expect and regret:   the intrusion of low-level stratus clouds into western Washington and Oregon. 

Usually occurring in late May, this year the transition came a bit early, with cloudy skies the rule today and yesterday over the western lowlands.

Below is the visible satellite image this morning.  The low clouds are stopped by the higher Cascades, and the Olympics are an island that extends above the clouds.

As an aside, the heavily irrigated eastern Washington is a sea of green.

The Seattle Panocam was well into the murk this morning (see below), and at my home in north Seattle, there was drizzle from the low clouds.

Yesterday was similar, and the high temperatures at many locations were below normal....the short heat wave is over!

As normal during our late spring June Gloom periods, the entire eastern Pacific is full of low clouds (the visible satellite image this morning is shown below)

The cool, moist marine air is only a few thousand feet deep, as shown by the temperature and dewpoint sounding at Forks, on the Washington Coast (red is temperature, green is dewpoint).  

When temperature and dewpoint are the same (in the lower portion of the sounding), the air is saturated...which means clouds!

Also note the strong inversion...temperature warming with height--above the cool air.  This inversion acts as a stable layer that prevents mixing of the low-level cool air into the atmosphere above.

Why do low clouds form in spring over the eastern Pacific?

Because of high pressure building aloft.  The weather map showing 500 hPa pressure (about 18,000 ft) for 11 AM this morning is shown below.

And at the surface:

Low-level high-pressure offshore pushes cool marine air into the westerm lowlands.  High pressure aloft creates upper-level sinking, which warms the air aloft.  This warm air creates the inversion that prevents the cool marine air from mixing with the dry air aloft.

We get stuck in this pattern for days or weeks this time of the year.   A good time for meteorologists to go on vacation.

Not All Temperature Records Are Equal

Some records are more significant than others.  

And some records are being used to hype normal temperature variability in unfortunate ways.

Consider yesterday (Sunday).   SeaTac Airport beat its daily record (77F0 for that specific date, reaching 81°F.   

The Seattle Times puts the 81°F day on the FRONT PAGE!  Must be a slow news day.

The Seattle Times story was heavy on hype, with several unfounded statements (see below).

Temperatures scorched past their record high.

Foreshadowing the inevitable summer of drought.  (This is total nonsense, by the way).

Should you worry about the RECORD high temperature yesterday?    Read on.

Why Monday's record did not mean much.

Monday's record high was a daily record.   

Daily records are frequently broken because there are so many opportunities to do so (365 chances each year!).    Breaking an annual record (the warmest day of the year) is much more significant.

Breaking the daily high-temperature record yesterday was particularly lame.  

Why?  Because the previous high temperature on that date (77F) was particularly low.  

You can see this by looking at the plot  (at SeaTac) of observed temperatures (blue lines) and record highs (red shading).   The previous record high temperature on that day (77F) was anomalously COLD.  The coldest daily high for ANY DAY IN MAY.    Even the end of April had warmer record highs. 

By the luck of the draw, May 3 never got above 77°F, and thus this was a record ready to be broken.  Low-hanging meteorological fruit.

The 81F record is still a low record high in May at SeaTac, cooler than ALL the other record highs for the month.

Breaking this wimply record has little meaning and does not foretell an inevitable summer drought as stated by the Seattle Times reporter (Conrad Swanson).

The latest forecasts are emphatic that there will be a cool down, with light precipitation returning.

The latest European Center Forecast has  SeaTac temperatures dropping to normal  (highs in the 60s).

Showers will return on Friday and Saturday (see below).

The kind of hype and exaggeration of heat and drought found in the Seattle Times and several amateur YouTube channels is unfortunate.

People are being misinformed and made to worry without cause.  Hyping climate change and exaggerating normal climate variability may get more clicks and revenue, but the costs of such misinformation are substantial.

There Is No Drought Emergency in Washington State

On April 8, Washington State declared a DROUGHT EMERGENCY for Washington State. 

 In fact, this is the fourth year in a row that the Washington State Department of Ecology has done so.

As described below, these drought emergency declarations are unwarranted and are contradictory to meteorological facts and the actual impacts.

Let me remind you about the definitions of emergency and drought.

An emergency must be sudden and unexpected, requiring immediate action to prevent imminent danger.  It is a crisis.   As I will prove below, this does not characterize what has happened in Washington this year or the past few years.

The term "drought"  means both MUCH drier than normal conditions and significant negative impacts of the dryness.

Half the years have below-normal precipitation.  Half the years have below-normal snowpack.  All these below-normal years are not drought years.

Let us consider the water situation this year.

The major reservoirs of our state are full or WAY above normal in water storage. Some examples"

Seattle:  much above normal.

Everett:  much above normal

The critically important Yakima River reservoir system:  FULL and much above normal.  

The Columbia River water levels are above normal, and predictions are for plenty of water for both irrigation and power. The Columbia is the most important source of irrigation water in eastern Washington.  It irrigates TEN TIMES the number of acres as the Yakima River. 

River levels in the state are all close to normal.

Precipitation over the State for the water year (October 1 to now)?

Above normal for most of the state,  and MUCH above normal in the mountains (that is why all the reservoirs are so full!)

Soil moisture?  Above normal!

Crop moisture?    Above normal in much of the state, nowhere below normal.

Current status of crops?    They are in excellent shape with extremely high yields for winter wheat. Apples look good as well

So with all this good water news, why is the Washington State Department of Ecology calling a drought emergency?

They claim it is because the state snowpack is below normal:  about half of average (see below).  This snowpack normally melts in May and June, helping to top off the reservoirs and support streamflow during the early to mid-summer.

Don't get me wrong.  It would be better if the snowpack were normal.  But there really is no water problem this summer with the current snowpack and certainly no drought.

First, 50% snowpack is not zero, and there will be substantial snowmelt water available during the next few months.   

Second, reservoir managers were very wise and used the above-normal precipitation of the past winter to fill all the reservoirs.  Better weather prediction supports this, since they can fill the reservoirs, knowing they would have time to partially drain them if a major storm approaches.

Third, and this is not advertised by the water fear mongers, Washington State gets much more precipitation (including snow water) than it needs, and much of the snowmelt moves down the rivers into the sea.

Fourth, Washington State agriculture can do quite well with below normal precipitation.   This is true of the Yakima basin farmers when they don't get their full allotment.  

What happened during the 2025 Drought Emergency?

The Washington State Department of Ecology is undermining its credibility with these inflammatory and unscientific drought emergencies.   

They would be wise to read some classical literature, such as The Boy Who Cried Wolf and Chicken Little (The Sky Is Falling).    One loses credibility when exaggerating threats.  Eventually, others don't take you seriously.

The Sky is Falling!

Warm But Not Hot

 During the first two weeks of May, there is often a short warm period that surges to 80°F or more, followed by a serious cool down.

This year will be no different.

Below are the forecast temperatures for Seattle.  Warming to 80F on Monday, followed by cooling into the upper 60s, with no major heat through May 11.

To illustrate this typical temperature pattern, below is a plot of temperatures in Seattle for April 1- May 31, 2024.  Observed temperatures are in blue and record highs in red.  Record lows in blue.

A major warm-up around May 9, followed by cooler temperatures the rest of the month.  Classic.  

You will notice that May brings the end of any frost threat.....good for gardeners to keep in mind.

So why do we often see a spike in temperatures in early May followed by cooling?

First, the sun has become strong in May, as strong as it will be in August.  Solar radiation at noon is summer-like, and days have become longer.  

Below is the solar radiation reaching Seattle since January 2025.  By May 1, we are really cooking.

To get warm temperatures, even in summer, we need a period of offshore flow, since onshore flow off the chilly Pacific will not allow us to get out of the 60s.

To produce the upcoming warming, this weekend will bring offshore-directed (easterly) winds, as illustrated by the winds, temperatures, and heights (pressures) around 5000 ft (850 hPa pressure) on Saturday morning (below).

Why do we typically have fewer really warm days later in the month?  

Because later in May brings extensive low-cloud areas over the eastern Pacific as high-pressure builds offshore.  This high pressure pushes the cloudy/cool air into western Washington. 

We call this "June Gloom," but it typically starts to move in during mid-May.

Here is an example of June Gloom cloudiness from last May.  Enough to make me want to grab a sweater.

Contrail Fest over Eastern Washington

The satellite imagery over eastern Washington this morning looked like someone had gone crazy with a white crayon,  drawing many white lines, most extending roughly east-west.

Here is a closer view.   The white lines are contrails created by aircraft.

Look very closely, and you will see some black lines as well:  the shadows are produced by the contrails stopping the sun's light from reaching the surface.

Contrails are formed by the combustion of jet fuel in aircraft engines.  This combustion produces water vapor that condenses into water droplets, which eventually freeze into crystals in the cold temperatures aloft.   Combustion particles aid the condensation.

Contrails are thicker when the air is already close to saturation.  Thus, contrails are particularly obvious when the air aloft is already moist.   

Look closely at the satellite imagery above, and you will see a thin veil of cirrostratus clouds, indicating air already at saturation.  Adding more water from the jet engines simply makes the clouds thicker.

Or we can look at the temperatures (red lines) and dew points (green lines) from the radiosonde (balloon-born weather observations) at Forks, on the Washington Coast (below).  Near the level at aircraft fly (marked trop on the figure), temperature and dew point are nearly the same, indicating a moist atmosphere near saturation! (the Y-axis is height in terms of pressure; 500 is about 18,000 ft, 250 is about 35,000 ft).

Temperature (°C)

Climate Change and Contrails

Contrails both cool that atmosphere (by reflecting solar radiation to space) and warm it (by emitting infrared radiation down to the ground).   

A number of careful studies have found that the warming is dominant.  

Thus, contrails contribute to global warming.  Much, much less than CO2, but still a contribution.

One way to reduce this warming by contrails is to alter flight paths to avoid cirrostratus clouds or regions where the upper troposphere (where planes fly) is near saturation with water vapor.   Some folks have suggested this be done.

In any case, the effects of contrails are relatively small, much, much smaller than the aggregate effects of global CO2 increases.