Serious Snow Coming to Regional Mountains

Note:  Announcement at the End

It is not unusual for the first notable snow to fall in the Northwest mountains around the middle of October, and this year will be no different.

Today's view from the top of Crystal Mountain, east of Mt. Rainier, is snow-free (see below).  It won't be that way for long.

A pulse of cold air will push into Washington State on Sunday and Monday, accompanied by moisture coming from the Pacific-- the result will be snow above approximately 4000 ft, with some flurries reaching 3000 ft.  And plenty of rain in the lowlands.

The snow total from the high-resolution UW WRF model through Sunday morning is shown below.  High elevation snow in the Cascades with more and lower-level snow on the eastern side of the Rockies.

This is just the start.  

By Tuesday morning, substantial snow will fall on the Cascade crest and its eastern slopes....as well as the mountains of NE Washington.  At some locations:  5-10 inches!

Extensive snow over and to the east of the Rockies.

Looking at the forecast temperatures at Stampede Pass, at around 4000 ft in the Cascades (below), we see the high temperature on Sunday will only reach 38°F.    With wet snow, it won't feel like summer anymore.   

The origin of the cool air?  From the Arctic!

On Saturday and Sunday, cold air will push southward over western Canada.  The map below shows the predicted temperatures around 5000 ft (850 hPa pressure) with the purple colors indicating very cold air (below 20°F).  From the Arctic to you!

On Monday morning, with low pressure along the Oregon coast and cold, high pressure over British Columbia and Alberta, cold air will be pushed westward across northern WA state (see map around 5000 ft below, with blue colors indicating cold air).   Winds are also shown, as are heights on the 850 hPa pressure surface (you can think of it as pressure around 5000 ft).

But why think only about snow?   The total precipitation by Tuesday morning is shown below.  Substantial amount (as much as 1-2 inches)  from the Cascade crest westward, associated with moisture circling around a low offshore.  

This represents the end of our wildfire season--which will be welcome by all.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk in detail about the outlook for the coming winter

The Last 70 Degree Day of the Year?

It is a bit depressing....

Today is probably the warmest day for the rest of the year in western Washington.

The last day temperatures in western Washington rise into the 70s.

The high temperatures today (Tuesday) are shown below. Lots of 70s around Puget Sound, with some low 80s over SE Washington.   Similar in eastern Washington.   It was wonderful.

Such temperatures are well above average and will plummet tomorrow as cool ocean air pushes inland.  And such warm temperatures will not return this fall.

To show you this depression situation, consider the latest surface temperature forecasts at Seattle and Pasco for the next 10 days (below).

Seattle HIGH temperatures will be in the low 60s and upper 50s through October 18.   This will feel quite chilly after the warmth of last summer.

Pasco will start in the low 70s the next few days and then decline into the 60s.

 A series of frontal systems will be moving through during this period, with rain spreading over our region.   For example, the total precipitation through Monday morning is quite substantial over the Oregon Cascades and the north Washington Cascades.

Obviously, this cool/wet weather will speed up the decline of the few remaining wildfires in the region.

The Northwest Interagency Coordinating Center has a graphic of the flammability of surface fuels (called ERC).   All regions of the area will become MUCH LESS flammable (going from red to blue in the graphic below).

Since the burned acreage this year is currently below normal over the region, we are guaranteed to end this year on the low side.

Changes in Ocean Temperatures

Several of you have asked about the ocean surface temperatures this year, so this blog will explore that issue.

Let's start with the current sea surface temperature (SST) over the northeast Pacific (below).

Cool surface water along the West Coast is due to the upwelling (upward motion) of cold water from below.  Cool water is also found to the north over the Gulf of Alaska. You have to go south of Baja California to get the really warm stuff.

How unusual are these sea surface temperatures? The next plot shows the difference from normal for this time of the year....also known as the anomaly.

Temperatures are actually a bit (about 1-1.5C) warmer than normal along the West Coast.

But cooler than normal in the Gulf of Alaska.

The sea surface temperatures are changing rapidly now due to the revving up of storm systems in the Gulf of Alaska, which are stirring the water in the vertical, bringing cooler water to the surface.  

This is an example of the kind of storm action (from Sept 27) that is doing the mixing.

Consider the changes in the SST over the past week (below).  

Wow.  In some locations, temperatures have cooled by more than 2.5C (4.5 F) in that short time.  On the other hand, some warming along the West Coast.

Why coastal warming along the coast?  Because low centers in the Gulf of Alaska weaken the northerly (from the north) winds along the West Coast, which reduces the upwelling of cool water from below.

Expect more offshore ocean cooling during the next few weeks as air temperatures cool and the storminess increases.

Talking of cooling, there should be substantial cooling over the tropical Pacific as a moderate La Niña develops.    

Meteorologists often look at a special zone in the central tropic Pacific (the Nino 3.4 area) (see below)

This area is now cooler than normal (blue colors in the figure below)

And the latest NOAA forecasts are for the cooling to strengthen.

At least, the Northwest will be relatively warm for the next few days before more wet/cool weather comes in this weekend.

Is Washington State Really Getting Drier?

The headlines and warnings about drought conditions have been increasingly strident, such as the Seattle Times article on low-water levels for the Yakima River Reservoir (see below). 

Several of the articles have pinned the blame on "climate change."

The current Drought Monitor Graphic (see below) indicates EXTREME drought over the North Cascades and southeast Washington.  Moderate or severe drought is suggested over the rest of the state!  

Considering the tendency of the somewhat subjective and drought-extravagant Drought Monitor product, let's examine the actual precipitation numbers (below).

Over the past year, the Cascades and southwest Washington have been considerably drier than normal.  But much of eastern Washington has actually been wetter than normal.

What about the summer (July 5- October 2)?   

Near or slightly below normal precipitation over eastern Washington.  Wetter than normal over the NW Olympic Peninsula and drier than normal over the western side of the central and northern Cascades.

The low Cascade snowpack last winter resulted in a lack of snowmelt in late June and early July.

As a result,  with less snowmelt, the Yakima River reservoirs fell below normal by mid-July (see plot below of this year's storage--blue--versus normal--red).

 By the way, last year (2024, green) actually had AVERAGE Yakima storage levels.  Currently, the Yakima reservoirs are about HALF of their normal levels.

There is no doubt that last winter was drier than normal.   But is this due to climate change or just typical natural variability?

We can easily examine this by looking at historical precipitation over many decades.

For Washington State as a whole, the trend for annual (September to August) precipitation for 1900 to 2025 (shown below) shows lots of variability, but little overall trend.

2025 has been drier than normal but hardly record-breaking....many years have had less precipitation.

There is a similar story for the Cascades from the crest to the western slopes (below) and for the eastern slopes of the Cascades (not shown).  A few recent dry years, but NO LONG-TERM TREND.

Although summer precipitation is relatively unimportant in our region (our summers are some of the driest in the nation), here is the trend of summer (June to August) for precipitation over Washington State.  Moist from roughly 1940-2000, but drier during the 1930s (before climate change) and recently.  

No real trend over the last century and a quarter.

That about climate models?  What do they suggest should occur with global warming?

I am in a position to show you this, since my group does such simulations.   Here is the plot of predicted precipitation change at Stampede Pass in the WA Cascade using a high-resolution climate model driven by very strong greenhouse gas forcing (RCP 8.5 for those familiar with climate change scenarios).

Precipitation INCREASES as the Earth warms. (The green lines show the average of many simulations)

The bottom line in all this?

There is no long-term trend towards less precipitation over the region during the past 120 years.  

Furthermore, climate models driven by increasing CO2 produce more precipitation over the region, not less.

As the planet warms, more of our mountain precipitation will fall as rain rather than snow, but reservoir systems, such as the Yakima's, can store the water no matter how it gets into the river. 

It might be wise to expand regional reservoirs to save more winter rain.

Extreme Precipitation Contrasts

Can you imagine a region in which rainfall can vary by a factor of 100, with 50 miles or less?

No need to imagine if you are living in Western Washington!

The map below shows the 24-h precipitation totals ending at noon today (Wednesday) over western Washington.

Over two inches over the southern and southwest sides of the Olympic Mountains, but only 0.01 inches around Sequim and Camano Island.  A factor of 200 between the rainfall at the two locations!

High-resolution computer model forecasts of rain (the total precipitation for the 36h ending 5 AM this morning) accurately predicted the huge variation (see below),  Two inches or more on one side, virtually nothing to the NE of the barrier.

There is a reason that the zone from Port Angeles to Sequim to Port Townsend to Whidbey Island is popular among retirees.

So what happened?   Moist southwesterly (from the southwest) air flow was forced upwards by the southern Olympics, producing lots of rain, but north of the mountains, the air descends, causing drying and little rain. (See graphic below).

Rising air cools by expansion as air goes from high pressure at low levels to lower pressure aloft.  That causes cooling--like you note when air escapes from a car or bicycle tire.  Cool air can't hold as much moisture as warm air, so water vapor condenses out as rain.

Sinking air warms by compression, causing clouds to evaporate and precipitation to cease.

You could see the drying yesterday on the northwest side of the Olympics in high-resolution visible satellite imagery, with a big hole in the clouds to the NE of the barrier (see visible picture).

The heavy rain yesterday ended the Olympic Peninsula fire season.    The Bear Gulch Fire is history.

With all the precipitation, all of the Olympic Peninsula rivers are now running at normal levels (green dots) or above normal levels (light blue and blue).

A Strong Cyclone is Developing Off the Northwest Coast

It is not as powerful as the "bomb cyclone" of last November, but it is impressive for this time of the year.   

Our first significant Pacific cyclone of the season.

The sea level pressure forecast for 5 PM today (Monday) shows the low center clearly, with a respectable central pressure of 980 hPa 

And you see the clouds starting to swirl around the low in the infrared satellite imagery.

The latest UW WRF forecasts are in....so let me show you what should happen.

Tomorrow (Tuesday) morning at 11 AM, the deepening low will be west of Vancouver Island, with an intense pressure difference to the south of the low...which means strong winds.    A strong front, with substantial pressure differences and winds, will be along our coast.

This low will not be in a hurry to leave us and is nearly stationary at 11 PM Tuesday.

Winds will get quite gusty late tomorrow afternoon and during the evening.  According to Seattle WindWatch, winds will gust to about 30 mph over Seattle later on Tuesday.

And the plot of predicted wind gusts at 8 PM Tuesday shows very strong winds (40-50 kt) over Northwest Washington and along the coast.   This early in the fall, you can expect some branches down and scattered power outages.

Finally, this offshore low should produce heavy rain over the Olympics and southwest BC, with loads of rain offshore.   The fire season west of the Cascade crest will be over.  And the windfires east of the Cascades will rapidly fade.

A Below-Normal Wildfire Year

 Being at the end of September, with cooling temperatures and substantial precipitation forecast, it is possible to make a definitive statement about the Washington wildfire season:  it is about to end and 2025 will come in below normal.  

During the next five days, there will be substantial precipitation across the region (see predicted totals through Wednesday afternoon below), and temperatures west of the Cascades will not get out of the 60s.  Much cooler east of the Cascades as well, with no thunderstorms expected.

This meteorology will close out the fire season, something supported by the guidance from the Forest Service Northwest Interagency Coordination Center, which predicts a dramatic drop in fuel flammability over the eastern slopes of the Cascades (see example below, where gray shading shows the normal values and the blue line shows the predicted values).

The fact that there are a few fires burning now should not make one conclude this is an above-normal year.   Wildfires are and have been a fixture of the Northwest environment.

But consider actual data.  

The figure below shows annual burned acres for Washington State since 2014, with the total for this year so far shown.  We are now below any other year, and with rain coming, one can expect only minor increases from the current total.  

There is little chance the 2025 total will reach the 10-year average (467,274 acres).

Similar results are found on the WA DNR website, which shows burned area for a subset of the above (the lower-elevation DNR lands).  This year has been below normal.

The fact that we had a modest wildfire year, even with a drier than normal summer, shows that the controls of wildfire are more complex than the trends in one or two meteorological parameters.  For example, wind is as important as temperature and moisture.

In a future blog, I will discuss this important point in more depth, noting we have experienced a wildfire DEFICIT over the region compared to historical norms.  

The Northwest is a place where wildfire is a normal part of the environment...and has been for thousands of years.

The Most Dangerous Day for Washington Wildfires for the Remainder of the Year

When it comes to rapid wildfire spread and growth,  strong winds are essential.

Virtually all major periods of rapid wildfire growth are associated with gusty winds.

It was clear that today would be a risky period on the eastern slopes of the Cascades.

Why?  Because we had some moderate fires going on the eastern slopes and strong westerly winds were forecast to push over and down the Cascades.

The Labor Mountain Fire Today

Before today, three lightning-initiated fires had been burning on the eastern Cascade slopes (see map):  the Wildcat fire east of Mt. Rainier, the Labor Mountain fire south of Leavenworth, and the Lower Sugerloaf Fire to the northeast of Leavenworth.

The visible satellite imagery this morning, around 9 A.M., clearly showed smoke from the fires, with the Labor Mountain fire being the most active (see below).

The satellite image of the heat emission from the fires confirmed that this fire was modestly active at 8 AM (the red dot shows the fire).

But when today's front approached from the west, cooler air flooded into western Washington, causing the pressure to rise.  This created a large pressure difference across the Cascades, forcing rapidly increasing westerly winds (winds from the west) down the eastern slopes of the mountains.

The UW WRF model predicted this change.  Consider the predicted winds near the surface over the central Cascades (below).  At  8 AM, the westerly winds were predicted to be modest, with the strongest near Ellensburg.

Huge strengthening by 2 PM

And the fire temperature observed from satellite around 1 PM clearly showed the fires increasing rapidly in response.

Surface observations documented the winds accelerating.  For example, the nearby Dry Creek USDA RAWS site showed the winds surging to around 40 mph.

A map of the maximum gusts today through 6 PM shows several locations with gusts over 30 mph east of the Cascade crest.

The great danger of the wind-driven Labor Mountain fire resulted in evacuation notices for those west of the fire (see below).

As of 8 PM, winds have started to decline, but fire-maintained gusts will continue for much of the night.

Good news.  In a few days, the fire danger for the whole region will recede as a series of wet Pacific fronts move in.