Substantial Precipitation Has Returned to the Pacific Northwest: What Has Changed?

The western U.S. weather pattern that has dominated most of the winter is collapsing and will not be returning.

With this change, substantial moisture will spread over the region, particularly the eastern side.

Enough precipitation that some of the exaggerated drought worries by some local media, amateur YouTube channels, and others should "evaporate."

The big change is evident on the latest visible satellite image, which shows a potent front making landfall on the Northwest 

There has been a lot of problematic information provided by some, so let me describe what has and probably will happen.

Overall Wet and Warm

The essential aspect of this past winter season for our region is that it has been wet and warm, with ample water to fill the reservoirs but sufficiently warm to reduce the snowpack by roughly 50%.

To demonstrate this, there is the precipitation data from October through April for Washington State from 1900 to 2025.   This year was a bit wetter than normal.

The plot for temperature is found below.  This year was considerably warmer than normal, although not a record (which goes to the crazy warm year of 2015).

Interestingly, our precipitation this year has been episodic, with very wet atmospheric rivers and extended dry intervals, something I will explain below.

So what has been going on?

This year, we had a very persistent upper-level (500 hPa, about 18,000 ft) pattern (see below).  The yellow/red areas indicate enhanced high pressure--also known as ridging.

Such a high-pressure area is associated with warm, dry conditions over the western U.S.   But since we were on the edge of it, sometimes an atmospheric river from the southwest or west could push in, giving us substantial precipitation (such as in December and March).  

Regional reservoir managers were very wise and saved the water from these short-period atmospheric rivers--that is why we are in decent shape right now.  They should all be given a gold star.

It is important to note that this persistent upper-level pattern has little to do with global warming, a claim in some media accounts. 

 I have read the literature on this issue and have published on this exact topic, so I am not speculating about it.  On the other hand, some of the warming (around 2F of it) may be ascribed to the slow warming of the planet due to increasing greenhouse gases.

The upper-level pattern is changing now (see below).  

Over the next five days, low pressure (blue colors) will dominate the West Coast from Alaska to Baja, with the "evil" high-pressure ridge (red colors) moving well to the east.

10-15 days from now is shown below.  

OMG.  A deep trough over our region.  That means wet.  

The lastest 48-h precipitation forecast for our region (below) shows substantial precipitation.  

Look closely....very substantial precipitation over the Yakima Basin!  The weather gods have heard us!  Or perhaps the weather gods want the Seattle Times to cool the hype. 

The Yakima water managers were very wise to reduce river flow this week, since their region will get a thorough wetting.

The rain is not going to stop.  The totals over the next 15 days are substantial (see below).  

Good news for agriculture, good news for weather supply, and good news for wildfires.

This precipitation will ensure that the Yakima reservoirs will stay full and should keep the westside reservoirs in good shape (they will fill, and there will be no need for irrigation in the west with rain falling).

The Weather Gods are Not Happy With the Weather Coverage 

of a Certain Newspaper

The Heaviest Precipitation of the Year Ahead in Some Locations?

If you ask most Washington State residents when the heaviest precipitation of the year generally occurs, they will tell you during the late fall and winter.  

It turns out that this is true for many, but not all, Washington State locations.    For some locations in eastern Washington, JUNE is the wettest month or at least equal to December.   

For example, consider Northport, a town in northeast Washington on the Columbia River (red marker on the map)

At this location, June has as much precipitation as December!  At some locations in northwest Washington and southeast BC, June is clearly the wettest month

How can this be?

One reason is that thunderstorms and convective showers are increasing rapidly this time of the year, with maximum thunderstorm activity in late June (see map below)

But there is another reason.....and we will experience this feature this week.

During the cool season, the westerly (from the west) jet stream is strong, and eastern Washington is in the rainshadow (see map of annual precipitation below)

But during May and June, the westerly jet stream weakens, and sometimes a trough of low pressure slides south of Washington, with moist southeasterly flow moving northward up its eastern side into eastern Washington.  No rainshadow!

This is exactly what is predicted to occur on Monday and Tuesday (see upper level map (500 hPa, about 18,000 ft) for early Tuesday).

Eastern (and western) Washington needs to be prepared for substantial spring rains.

The total through Wednesday morning is substantial in the west, and much of eastern Washington gets moistened.

Another low-pressure trough will move in later in the week, with the accumulated precipitation total through Sunday at 5 PM shown below.  Very, very substantial amounts in eastern Washington and Oregon.  Less irrigation will be needed next week.

 Enough precipitation over the Olympics and eastern Washington that I suspect the drought talk should fade.

 

A Wet Memorial Day

 If you are planning an outdoor excursion on Memorial Day (Monday), I have a suggestion:  bring an umbrella and wear a warm jacket.

Consider the latest forecasts.  The total precipitation through Sunday at 5 PM shows only a little drizzle on the windward side of some local terrain.

But on Monday, a strong upper-level trough will move in (see upper level map below, with blue indicating lower pressure than normal...troughing), producing much colder than normal temperatures (highs in th 50s) and substantial precipitation.

Here is the forecast precipitation total through Tuesday morning:  western Oregon and Washington will be thoroughly watered down, with some rain extended over the Cascades into Yakima and Kittitas counties. 

More precipitation is predicted for later in the week.  In fact, the regional totals through early June are scary wet (see below).  Perhaps this will comfort folks worried about drought. 😊

It is important to note that Memorial Day weekend is infamous for wet conditions in our region.  It illustrates this soggy fact, below is a plot of the historical precipitation at SeaTec from May 23 through May 28.

Most years have some precipitation over that period...and occasionally it gets quite wet (almost 2 inches).   This year, we will enjoy about a half inch over that period, so we will be a little wetter than normal.     That's fine...we can use it.

Why the Washington Drought Emergency Should Be Dropped Immediately

It is time to clear the air.   

To definitively correct misinformation being pushed by a Washington State agency, the Seattle Times Climate Times Climate Lab, and some amateur YouTube channels.

The claim that this summer represents a DROUGHT EMERGENCY for Washington State.   

It is simply and demonstrably false.

In a previous blog, I showed that our reservoirs are fuller than normal, soil moisture levels are good, our annual precipitation is at or above normal, and that current crops are doing well. 

But like some vampire, the drought claims can not be killed so easily.   

In particular, the media, YouTube amateurs,  the State Department of Ecology, and others are pinning their drought claims on the Yakima River drainage and this year's low snowpack.

Below, I will demonstrate why they are very much wrong. 

Yakima and Kittitas counties, through which the Yakima River flows, are relatively arid locations, being located in the rain shadow of the Cascade Mountains (see below).

Only with substantial irrigation can they provide the agricultural bounty for which they are well known.

This irrigation comes from two sources.  

Much of Yakima and Kittitas agriculture gets its water from the Yakima River, with some contributions from the Columbia on the eastern side of the area (see map below).   Everyone agrees that the Columbia will have plenty of water this year, so there is no suggestion of drought for the majority of the irrigated land in eastern Washington (blue, purple, and yellow colors below)

The Yakima River drains off the Cascades, starting near Snoqualmie Pass, and is also fed by a few tributaries, such as the Cle Elum, Teenaway, and Naches rivers.

These rivers are mainly fed by mountain rain and melting snow.  Since most of the precipitation falls in winter and spring, while most of the irrigation demand is during the dry summer (particularly July and August), water storage is required.

One source of storage is the Cascade snowpack, which does most of its melting in May and June.  Thus, snowmelt is only a short-period source of water... a fact that will be important later.

And then there are the Yakima River Basin reservoirs (see below), which are filled by both rainfall and snowmelt.

And finally, there is spring and summer rainfall, which is modest in this region.

To fully supply water for all agricultural and human needs of the Yakima irrigation district requires about 2.3 million acre feet for April through September.    The reservoirs can hold about 1.1 million acre-feet, or roughly half what is needed.

The remainder must come from the river flow, supplied by either mountain rain or snowmelt.   

A big issue is timing:  only the reservoirs can supply a large amount of water during mid-summer (July and August) when demand is greatest.  

Keep this fact in your mind...it is crucial.

Now, let's consider the water situation this year.   The annual precipitation was actually wetter than normal over and near the Cascades (see difference in normal during the water years from October 1 to  May 6, below).  So plenty of water falling from the sky.

But much of this precipitation was associated with warm atmospheric rivers and substantial amounts fell as rain, particularly at lower to middle elevations.   Particularly strong atmospheric river events occurred in December (which produced substantial flooding) and March.

Because of the warmth of those atmospheric rivers, the snowpack was below normal this season over the central and southern Cascades, with the Yakima Basin topping out at around 50% of normal (see below).  Not zero, not 20%.   This is going to be important as well.

The substantial precipitation and the wise actions of those running the Yakima reservoirs have led to the Yakima reservoirs filling well in advance of normal.   Filling early without the need for snowmelt.    

Check out the figure below, which shows the water storage this year (blue line) compared to normal (red line).  Stunning.  We are already above the normal mid-June peak!

The Yakima Reservoir storage will remain topped off for several more weeks.  Why?   There is still considerable snow left to melt at higher elevations in the Cascades during the next week or so (see below).

.And the current model forecasts indicate substantial precipitation over the region next week (see totals through next Saturday).

There will be plenty of precipitation and snowmelt to keep the Yakima Reservoir system topped off through the end of the month.  No drying heatwaves are forecast during this period.

With Yakima Reservoir full in early June, there is a near certainty of sufficient water for Yakima County agriculture this summer.

I am not speculating....I checked.   Full reservoirs starting the summer are associated with ample water for agriculture in Yakima and Kittitas Counties.  There have been no examples of serious agricultural water issues for years in which these reservoirs start off the summer full. 

So how could the Department of Ecology and others get this so wrong?

They did not consider several unusual aspects of the past year.   

We started off with very low river and reservoir levels last fall.  But then we had crazy heavy warm rain in December, which caused a massive increase in river levels on both sides of the Cascades.   To illustrate, the figure below shows the flow on the Yakima River at Umtanum over the past two years (see below, black line).  Then, in March, another major event occurred.  Both were at record levels (dark blue lines)

Knowing about the low snowpack, the Yakima system water managers saved a portion of the huge influx of water,  pushing storage WAY above normal.  Very wise.

Normally, some of the melting snowpack is used to fill the reservoirs, but because of the heavy rain, it was not needed.   Thus, the melting snow could be used simply to keep the reservoir topped off and support reasonable flows.   

Because of the above-average precipitation last winter and the full reservoirs, we did not need to have a normal snowpack this spring..... 50% could do.   And the substantial rain also provided soil moisture west of the Cascades.

Those falsely calling for a drought emergency love to note that reservoirs can only hold about half the needed water for Yakima irrigation, and thus, they suggest that we need 100% snowpack to get through the summer. 

False!

But they are thinking too simplistically.  During the spring and early there is still substantial precipitation and water draining into the system, providing water for irrigation and other uses.  And we never use 100% of the snowpack water, with substantial amounts running into the sea.   Don't believe me?  Here is the average flow at the Dalles on the Columbia River.

A snowpack with 50% of normal snow still has a LOT of water.

In summary, the Drought Emergency Declaration by Washington State should be dropped immediately.  

Washington State residents deserve accurate information.  Washington agriculture should not be undermined by ill-advised, unscientific declarations.

Funnel Cloud in the Lowlands and Substantial Snow in the Mountains

Very active spring weather has been occurring over the Northwest, with substantial snow above 4000 ft and unstable air that has brought heavy showers and even a mini-tornado!

First, the snow.   Here is a cam shot this morning at Paradise (Mt. Rainier) at around 5400 ft.  Impressive snowfall!

Hurricane Ridge on the Olympic Mountains (around 5200 ft).  Beautiful

Even the relatively low elevation of Stevens Pass (around 4000 ft) received significant snowfall.

All of this white bounty is the result of very cold, unstable air moving into our region, which is illustrated by the visible satellite image this morning (below). 

The blue arrow points to the unstable air, characterized by showers and sunbreaks.  The instability showers are driven by a large change in temperatures with height, with cold arctic air passing over relatively warm water.

Since current, low-level winds are from the west, there are rainshadow regions downstream of the Olympics and Cascades (areas of lack of clouds are evident there).  

Substantial new snow has been falling above 4500 ft, such as at Paradice on Mountain Rainer, where nearly 15 inches have fallen (see below)

Precipitation over the region during the past 48 hr has been substantial, with many locations in the mountains getting 2-3 inches of liquid water (the observations are shown below).

As I have discussed in previous blogs, the claims of extreme drought over the region are inconsistent with the facts on the ground (and in the air).    There will be plenty of water this summer for all uses,  particularly with the full reservoirs of the region.  

Snowpack was low, but substantial, and well-timed total precipitation (which was NOT below normal) ensures that water will not be a problem this summer.

Now for the fun part of the blog.....we had another funnel cloud over Puget Sound....a mini-tornado if you like.

One formed yesterday (Friday) over southwest Seattle around 8 PM.    The rotating cloud was captured by Matt Young, a relative of one of my colleagues at the UW.

This weak tornadic event was associated with a modest area of convection (cumulonimbus clouds), which is apparent in the radar image around 8 PM (below).

Funnel clouds associated with weak cumulus convection (produced by unstable air) are not unusual over Puget Sound.   There is a lot of horizontal wind shear around here (winds changing rapidly in distance), with wind shear having essential rotation (see schematic below).   

The upward motion in convection can "spin up" this rotation into a weak vortex....something I have blogged about many times before.

Puget Sound Convergence Zones are famous for being associated with such weak funnels, something I describe in my Northwest weather book.

Puget Sound is not Oklahoma, where several thunderstorms and tornadoes are frequently threatening.  But weak convective funnels occur all the time around the Puget Sound region.

Snow in the Mountains and Wet

The rapid transition to cool, wet conditions occurred yesterday, with temperatures in Seattle declining from 80F on Tuesday to 58F in Wednesday.   Major cooling.

Cool and wet enough so that substantial snow fell above 5000 ft (see Paradise and Crystal Mountain cam imagery below).

During the past 48 hrs, there have been large amounts of precipitation in the Cascades, with one location near the Spada Lake reservoir getting almost 4 inches!  Lots of precipitation to moisten the crops in eastern Washington.

The cool/wet weather is not over.  A very potent front is now approaching our coast (see current satellite image below).  Cold/unstable air is behind it (area with clouds and openings on the left side of the image).

Below is the forecast precipitation total through Sunday morning.  

Substantial amounts (1-4 inches) on the western side of the Cascades and near the crest.  Substantial amounts on the SW side of the Olympics.

Temperatures will be low enough that substantial snowfall will occur above 5000 ft (see below).

This precipitation is very well timed and will push up river levels on the eastern side of the Cascades, which have been lagging due to below-normal snowpack (see below for the Yakima River)

The fact that the Yakima Reservoirs are now full and will remain full for the next several weeks bodes well for the water supply this summer. 

"Perfect Storm" Rainfall Comes to the Northwest

It has happened multiple times this past year.   

After an extended dry period, the circulation pattern changes, bringing wet conditions that get us close to normal again.

This is going to happen again starting tomorrow. 

The predicted accumulated precipitation through Thursday afternoon will be substantial in the Cascades, and even eastern Washington will enjoy a general moistening. (see below)

Importantly, the precipitation will continue!  By Sunday afternoon (below), some locations in the Cascades will enjoy 2-4 inches.  This will cause rivers to substantially rise on both sides of the Cascades.

Temperatures will dramatically cool for the remainder of the week....with highs declining to around 60F over the western lowlands (see below).

Cool enough that snow will fall at higher elevations (see below)

The storage for the Yakima River basin has remained full (see below).  This wet/cool period will guarantee it remains high for the remainder of the month. 

River flows are below normal because of the lack of snowpack, but flows should be close to normal after mid to late June when reservoir releases are dominant.

The precipitation and relatively cool temperatures will ensure that soil moisture remains in good shape (currently, 78% of the area is adequate)--see below:

If any of you were considering planting seeds or plants, THIS IS THE TIME TO DO IT!  Soils have warmed, and precipitation will keep the ground moist.