A Guaranteed White Christmas (In the Mountains)

For lovers of Northwest snow, I have good news.  

Bountiful mountain snow is GUARANTEED before Christmas.

Yes, this means you will be able to hit the slopes on some of the higher elevation regional ski areas.

Consider the latest 120h forecast for accumulated snowfall from the UW weather prediction system (below).

A big snow dump in the mountains, with over 3 feet of snow at some locations.  

What about the highly skillful European Center model snow forecast for the same period? (see below)

Same story!  Lots of mountain snow.

I know what you are thinking.  

Can we trust these snowy predictions?

Good question.  To evaluate their reliability, let's look at the NOAA ensemble of many forecasts for snow at Stampede Pass in the central WA Cascades (at about 4000 ft).

The individual forecasts are shown by the gray lines and their mean by the black line (below).

All the forecasts have lots of snow, with a mean of about 40 inches by Christmas.

You can see why I offer a guarantee.   Lots of snow is a sure thing.

So get your skis and snowshoes out.  There will be plenty of snow at the high-elevation ski areas.

Guaranteed.

Drought Exaggeration

One of the most misused terms is drought.    Certain groups and individuals are constantly using the "D" word when it is not appropriate, often to support their own agenda.

The most frequent source of the most exaggerated, unfounded drought claims is the Drought Monitor graphic, produced by a partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration (see the most recent graphic below).

The trouble is that these graphics are subjective and often wildly wrong.  

And they are virtually always wrong in the same direction: exaggerating the intensity of the "drought."

Want a good example?  Consider the LATEST Drought Monitor graphic for Washington State released on Thursday (see below).  It shows the conditions for last Tuesday morning

Moderate drought over western Washington, most of the Cascades, and the eastern slopes of the Cascades.  Severe drought over the western slopes of the central Washington Cascades, the eastern slopes of the Cascades, and northeast Washington.   EXTREME drought over southwest Washington.

Drought during a period of flooding, moist soils, and above-normal reservoir levels.

How can I put it diplomatically?   

This is inconsistent with reality.

Climate advocacy groups, such as the Seattle Times Climate Lab, take exaggerated drought claims like this as gospel, and hype is further. (see below)

So, When Should We Use the Term "drought"

Some groups, like the Drought Monitor folks at the University of Nebraska, call it a drought when rain or snow are simply below normal.

This makes little sense, since precipitation will be below normal half the time.  So 50% of the time we are in drought?   Silly.

And what about impacts?   A drought must produce serious problems due to a lack of water.

More scientifically grounded groups, such as NASA (below), use such a definition.

There is no way our region is in drought, by any rational definition.  

During this fall wet season, most locations received MORE precipitation than usual.  

To illustrate, here is the difference from normal over the past 60 days. Most of the state was above normal, with large areas receiving MUCH more precipitation than normal (the North Cascades).

The biggest drought concern has been the Yakima Valley and its reservoirs, with the latter being significantly below normal at the end of the summer.

Now the Yakima reservoir levels are MUCH  higher above normal (see below).

Local rivers? Most are flowing much above normal (see below).

Westside reservoir storage?  All above normal (Seattle shown below).

The water level in Lake Roosevelt, behind the crucial Grand Coulee Dam?  Above normal!

 

Soil moisture? Large areas are above normal (green colors)

The only aspect that is below normal right now is regional snowpack, but being low in mid-December is not unusual, and lots of snow is expected during the next week (and has been in the forecast for over a week).

As shown below, the snow situation for the Columbia Basin is excellent (well above normal), and the north Cascades is at 77% of normal.    The Yakima basin has about half of its normal snowpack.

A major enhancement of snowpack is now forecast, with huge amounts predicted for the Cascades during the next five days (see below). 

In short, there is no rational reason to suggest that Washington State is now or will not be in drought during the next months.      

And there's something else.

Washington State receives far more precipitation than it needs.  Thus, a modest dry period (such as last spring and summer) had relatively little impact on the economy or essential water resources.  You really should not use the term drought when impacts were not evident.

The Incoming System

 I wanted to provide a brief update on the incoming system.

A strong front is approaching, which will bring modest winds and substantial mountain precipitation...but nothing like we endured last week.

The latest forecast precipitation totals through 4 PM Monday is for "only" 3-5 inches in the Olympics and northern Cascades.

That will drive some of the local rivers up to moderate flow levels, but not nearly as high as last week.

Here is a sample for the Snoqualmie River,  where levels just reach major flood levels.  Also, a much lower peak this time.

Then there will be some winds associated with a strong cold front and the low pressure accompanying it. 

This forecast surface map for 7 AM Monday shows the  pressure pattern (solid lines), winds, and temperature (shading).  A strong front is offshore at this time, with a large north-south pressure difference over western Washington.  That means strong winds from the south.

By 4 PM, the front has moved in, and cooler air has swept into western WA.  A big pressure difference across the Cascades means strong winds descending into eastern WA.   Good for wind energy, bad for power outages around Ellensburg and Leavenworth.

Here in western WA, wind gusts should reach 40-50 mph, as illustrated by the Seattle WindWatch graphic for Seattle (below).

A few outages should be expected in western Washington--tens of thousands, but no more.

Finally, the big upcoming weather story will be SNOW.   Lots of it in the mountains, as illustrated by totals through next Sunday (below).

The Other Weather Disaster Last Week: A Downslope Windstorm

Although the big local weather story this week has been the heavy rain and serious flooding over the Pacific Northwest, there WAS another extreme weather feature:   powerful downslope winds on Wednesday that caused massive tree damage and power outages over the eastern slopes of the Cascades.

Some of the winds exceeded 100 mph from the west.

Leavenworth, on the eastern slopes of the Washington Cascades, was hit particularly hard, with the entire town losing power, forcing the cancellation of the Christmas Lights festival.  Here are a few samples of the destruction:

The maximum wind gusts on Wednesday (from the limited collection of locations with power) are shown below. 106 mph above Lake Wenachee, 112 mph at Mission Ridge, 77 mph on the slopes just above Leavenworth. Much lighter winds over the lower Columbia Basin.

The winds at Mission Ridge (6730 ft) are shown below (the dark blue line indicates the sustained wind, the top of the light blue area indicates the gusts, the bottom of the light blue indicates the low winds during the hour).

Very windy from early Wednesday through early Thursday, with many gusts over 100 mph.   And the winds were exceedingly gusty.

 Were these winds predicted ahead of time?   You bet they were.  Below is the forecast surface winds from the UW WRF modeling system for 1 PM Wednesday.  

Reds are over 70 knots (81 mph).  You can see bands of localized strong winds on the eastern side of the Cascades.  

The NOAA high-resolution model (HRRR, High Resolution Rapid Refresh) was doing the same thing, as shown by the forecast wind gusts at 7 PM Wednesday.

So why such localized winds?    

Answer: There was a downslope wind event in which strong winds approaching a mountain barrier are accelerated as they descend the lee slopes (see schematic below).

Favorable conditions include strong winds approaching the barrier with sufficient vertical stability, conditions that can occur with the passage of the weather system from off the Pacific or the approach of a strong atmospheric river, which occurred during that day.

The eastern slopes of the Cascades are well known for strong downslope winds. In my Northwest weather book, I note several incidents.

Finally, many of you would like to know whether another major atmospheric river is headed to our region.   The answer is yes.

Here is the atmospheric river diagnostic for Monday morning.  A juicy plume heading right into us.

Consider the predicted precipitation totals through next Friday.

Yikes!  Some places will get over 10 inches. On top of saturated soils and rivers that are running high. Some rivers will flood again.

Will discuss in future blogs.

The Atmospheric River Event is Ending--- And ANOTHER One is Predicted

The heavy rainfall is over, but some rivers are still rising.   The most impactful atmospheric river event of the past few decades.

Consider the 5-day rainfall totals below, and be prepared to be impressed.  

Many of the windward slopes of the Cascades and Olympics received more than 10 inches, with some experiencing 15-17 inches.

You will also notice extreme rain shadow areas in the lee (east) of major barriers, which received less than an inch.

Numerical weather prediction models were STUNNINGLY good, as shown by the predicted 5-day precipitation totals by the UW WRF model made last Sunday (see below).  

Close correspondence between predicted and observed rainfall.

The weather prediction world has changed dramatically during the past decades, with virtually every major extreme weather event predicted days before.

The problem is that governments, local agencies, and others are not sufficiently taking advantage of these skillful forecasts to save lives and property.  The media do not understand the profound impact of improved weather prediction technology.  

This problem is compounded by the National Weather Service, whose forecasts and warnings have declined substantially compared to the state of the art.  

 I can provide a half-dozen cases of the NWS failing to provide timely warnings even when model forecasts are excellent, such as this event and the Seattle ice storm of December 2022.

I hate to reveal this, but  ANOTHER significant atmospheric river/precipitation event is in the forecast.

Consider the predicted 72-h precipitation total ending 4 AM on Thursday.  Yikes...pretty wet, with some mountain areas getting 10 inches.  This is problematic, falling on saturated soils and rivers already well above normal.

To address the reliability of this forecast, one should consult ensembles of many forecasts.  Below are plots of forecast precipitation at Stampede Pass in the central Cascades from many forecasts.

All are going for a major precipitation event starting in the middle of next week.  You can take this to the bank.

All of this is a reminder that the most impactful severe weather of the Pacific Northwest is flooding.  Not heatwaves, not wildfires, not windstorms.

The Second Atmospheric River Will Bring Far More Severe Impacts

In act one of this meteorological drama, yesterday and this morning brought heavy rain and flooding to many sections of western Washington.  Well-predicted days in advance.

But the weather prediction models indicated that this would be a two-act event, with the second act being far more serious.   The curtain is about to rise.

Take a look at the precipitation totals of the first act (last two days, below).  Some areas received 7-8 inches.

Many local rivers are now at flood stage, with some at record levels (black dots are record levels, blue are 90th percentile or greater, with normal being 50th percentile)

The media is full of pictures of flooded roads, such as in the Snoqualmie Valley.  A once-in-1-3-year event.

But this is just the meteorological appetizer course.  The real action is about to begin:  a second, stronger event that will throw massive amounts of rain on saturated surfaces.

Consider the total precipitation from the UW ultra-high resolution modeling system for the 72 h start this morning at 4 AM (shown below).

Wow.  There are going to be some happy ducks.  Large areas will get 10 inches of rain or more, particularly in the Olympics and northern/central Cascades.

Serious flooding is inevitable.   

How can I be so sure?  Because of the use of ensembles of many high-resolution forecasts.  If they are all on board with heavy rain, my confidence grows.

Let me demonstrate this to you.   Here is the ensemble of accumulated precipitation at Humptulips on the southwest side of the Olympics.  A huge amount of precipitation (about 6 inches), most over about 12h.   Not much variance in the forecasts.

Stampede Pass in the central Cascades (below)?  A similar soggy story.

Every reservoir in the region will reach normal or above normal levels.  Consider the Seattle Times' favorite drought reservoir system (the Yakima), which they featured in a recent story.

The Yakima River is now at flood stage (see below), and in a few days the entire system will be full to normal levels.

The Torrent Has Begun: The Philippine Connection

The predicted rain has begun.  Rain associated with a potent atmospheric river, with some of the water originating thousands of miles away near the Philippines! 

Consider the situation on Sunday afternoon, as shown by special satellites that observe atmospheric moisture from space (below).  

You can see the plume of atmospheric moisture extending from the western Pacific to the Northwest.

But it is not quite that simple.  There is substantial three-dimensionality to atmospheric rivers.

To prove this to you, below are air trajectories--the three-dimensional motion in space--of the air reaching the Cascades at 10,000, 5000, and 2000 meters above the surface.   At high altitudes, the moisture is coming from the western Pacific, but at lower elevations, the moisture is coming off the Pacific to our south.

Atmospheric rivers are like real rivers, with tributaries contributing moisture along the way.

The big precipitation has started.  Below are the precipitation totals for the past 24h.  

 A number of locations have already received 3-4.5 inches.   And more is on the way.

Our rivers are rising very rapidly.  For example, the levels of the Cowlitz River in SW Washington are zooming upward (see below).   Soon it will be at flood stage.

Remember...this is a two-step event...and this is only the first part!

The Seattle NWS Forecast Office has FINALLY put out flooding warnings over large areas of western WA (see below).  Quite honestly, they waited way too long to do this.  

This is a serious event, and people need time to prepare.