December 07, 2023

The Darkness

 It has been often said that it is darkest before the dawn.

Well folks, we have been very dark and dawn is a long way off.

The image from the Seattle SpaceNeedle at noon Wednesday, was dismal at best (see below)

So what do the numbers say?  How dark have we really been?

Below is a plot of incoming solar radiation from the WSU AgWeather network site in Seattle (near the UW) over the past year.  

The last two days have been abysmal, with 0.57 and 0.87 MJ (megajoules) per square meter.  During the midsummer we often get above 30.

To put it another way, during mid-summer we can get around 50 times more warming rays from the sun than during the past few days.  

What about Pasco in the Columbia Basin?  Surely that location would be brighter! (see below).  

Nope, the same story.

The trouble is that we start with a relatively northerly latitude with short days.... so there is meager solar radiation to start with.

Then we add very thick, deep clouds from a strong atmospheric river. Plus lots of precipitation.  The visible satellite imagery at noon for December 5 and 6 are shown below.  The atmospheric river/frontal clouds are clearly visible and had spread over both sides of the Cascades.

The combination of weak sun, short days, and plentiful clouds makes solar energy problematic in our region during the winter.    Take a look at the average solar resource (the fancy name is irradiance) for December.  Not much in the Northwest.  A different (and better) story over the desert U.S. southwest.

Weather forecasting models predict solar radiation reaching the ground, something I have never shown in the blog until today.  But now I will give you a peek!

The forecast for 1 PM today shows dark colors (less sun) over the region with the murk being particularly bad over the western slopes of the Cascades.

Saturday looks better in northern CA, but far worse in western Oregon and Washington.  Why?  Because ANOTHER atmospheric river is coming in.

Want solar relief? It will be much brighter on Tuesday (see below) as a ridge of high pressure builds (temporarily) over the eastern Pacific.  

Get your sunglasses ready.😊

December 05, 2023

Subtropical Warmth, Heavy Rain, and Filling Reservoirs

You did not have to travel to Hawaii this morning to experience subtropical warmth or tropical-intensity showers.  It was here in the Pacific Northwest.

As a substantial atmospheric river interacts with our terrain, large amounts of precipitation have fallen during the last 36 h, with extreme contrasts over a few miles.

Before are the 36-h totals.  Some locations over NW Oregon and SW Washington got to around 8 inches...and more is coming.  6-7 inches in the Cascades.

But as impressive as the large totals are (breaking daily records at some locations), the LACK of rain in some amazing rainshadows is also notable.  

Consider the rain shadow northeast of the Olympics.  Over the higher terrain, there were over 6 inches in 36h. In contrast, a station west of Port Townsend only had 0.12 inches, and portions of Whidbey Island were only about a quarter of an inch (see below).

To put it another way, there was about a fifty-fold difference between the rain at higher elevations and downstream in the rainshadow.   Amazing.

The air over us has felt subtropical.  The temperatures this morning have gotten into low-60s  (see proof below).  The dewpoints (a measure of water vapor content) rose into the mid-50s.   

The freezing level (the level of the atmosphere where temperature declines to 32 F) was as high as 11,000 ft this morning based on the Salem, OR radiosonde (see below).   All rain in the mountains!

All this warm rain is rapidly filling our reservoirs, which is a good thing.  The water level in the big Chester Morse Lake that supplies a large proportion of Seattle's water is going up fast (see plot below).

Finally, let's get back to the subtropical origins of the air over us.  Below are 72h trajectories.....3D paths over time... of the air that was over Seattle this morning ( I used the wonderful NOAA Hysplit website to create these).

Our air started around 30N//.the latitude of northern Baja California!  The air did not come from Hawaii, so let's not call it a Pineapple Express. 😀

Things will dry out a bit for the remainder of this week before ANOTHER atmospheric river reaches our shores on Saturday (see below)--so keep your umbrellas and rain jackets handy!

December 03, 2023

A Potent Atmospheric River Will Bring Heavy Rain and Some Flooding to the Northwest

If some folks thought that a strong El Nino would protect the region from heavy rain before the new year, they were mistaken.

A substantial atmospheric river-- a narrow current of high-water vapor content-- will be heading right into our region starting Monday evening, and the precipitation amounts will be substantial.

Let me show you.

Below is a forecast map of total water vapor content through a vertical column of the atmosphere at 10 PM Monday.  The blues and light pinks indicate the largest values.    

Atmospheric rivers like this tap large amounts of water vapor in the tropics and subtropics.   Moisture also converges into the "river" from the sides, not unlike the water of small streams flowing into a major river along its path.

Professional meteorologists generally prefer to look at another measure of the potency of atmospheric rivers called integrated water vapor transport (IWVT),  which is water vapor content times the wind speed.  

It is a measure of how much water vapor is being transported by the wind and is better correlated with rainfall potential.

Here is the IWVT at the same time as the image above (10 PM Monday).  Blues indicate large values.  

You will note that there is a lot of moisture coming into the Northwest coast, but little extending to the northeast. Where did all the moisture go?

It rained out!

Below is the forecast total precipitation through Monday at 4 AM (start at 4 AM Sunday).  Precipitation for the whole region, but heaviest over the Oregon terrain.

Then the atmospheric river comes in (JAWS music should be played now).  The total precipitation through 4 AM Tuesday is impressive, with 7-10 inches over the mountains of Washington and SW British Columbia.  Most of that atmospheric river moisture is being pulled out of the atmosphere by precipitation over regional terrain.

One day later even more, particularly over Oregon.  

Soils are now saturated throughout the region.  Adding this precipitation will result in rapidly rising river levels, some to major flood levels.

Consider the forecast of the NOAA/NWS Northwest River Forecast Center (see below).  A number of rivers will get to major flooding (purple) and others to major flooding (red).

Consider the Snoqualmie River near Carnation.  It will get considerably above major flood stage and will set a record for the period.

Do you want to see something very, very impressive?  Go to Snoqualmie Falls on Wednesday.  You won't believe what you will see.

One thing I can guarantee you.  The City of Seattle will be able to bring the water level of its reservoirs way up and there won't be any talk of low water levels.  Take a long shower if you like....😔

Considering that we are in a strong El Nino period, which will probably reduce snowpack in the spring, reservoir managers should try to save as much of this water as possible.

December 01, 2023

Strong Winds and Heavy Mountain Snows Coming to the Pacific Northwest

After a period of high pressure, weak winds, fog, low clouds, and little precipitation, the weather in our region is about to get quite intense and interesting.

Strong winds will soon buffet western Washington and heavy snow (multiple feet) will fall across our regional mountains.

A front went through this morning and our region is now in moist, unstable northwesterly flow as shown by the visible satellite image this morning (below).  The white and dark areas offshore are convective showers and you can see the intense cloudiness on the western slopes of the Cascade associated with substantial snow showers.

White-out conditions are now occurring in the mountain passes, illustrated by the WSDOT pass cam below.

Let me show you predicted snow accumulations from the latest University of Washington model forecast.

Through 4 PM the Cascades will get as much as 6-12 inches, and eastern Washington be whitened.

The total through 4 AM Saturday is much more impressive, with 1-2 feet over higher terrain.

And by 4 PM Saturday, many locations will have experienced 2-3 feet.  Substantial snow will fall over northeast Washington and northern Idaho.

The snow season will begin with a bang and many ski areas should be able to open.  Travel across the passes should be dicey during the next keep that in mind.

The regional snowpack had declined to about 50% of normal.  By Sunday, we should be at or above normal levels in most locations.  I should note that other modeling systems (such as the European Center) agree with this forecast.

And then there are the winds.....

 Some of you will experience power outages overnight.  I am charging up my devices as soon as I get home from the UW!

A low-pressure system will move eastward to our north, creating a large north-south pressure difference across western Washington (see forecast surface pressure map for 4 AM Saturday).  That means strong winds.

The latest NOAA HRRR forecast (available on the City of Seattle Windwatch site built by the UW) predicts powerful winds overnight. 

 Below are the forecast gusts at 1 and 3 AM.  First, the coast and NW Washington will get hit and then Puget Sound, some with winds exceeding 50 mph.  Such winds guarantee some power outages.

The only good thing is that many trees have lost their leaves, making them less vulnerable

Considerably more active weather is predicted beyond this weekend, including heavy rain and potential flooding, including a major flood on the Snoqualmie River (see the NW River Forecast Center plot below).  

I will talk about that threat in a future major weather challenge at a time!

November 29, 2023

High Pressure and the Northwest's Low-Cloud Affliction

 The visible satellite image this morning was stunning.

Low-elevation clouds covered nearly all of Washington, except for the highest elevations (see image)

Some folks were in fog while others looked at a low-stratus cloud deck.

And this cloudy murk was cold, with much of the state below freezing (see minimum temps this morning).   Freezing fog was widespread.

Cold, cloudy, foggy and icy.  Yuk.

What can you blame for this unpleasant situation?   

Persistent high pressure.  A strong ridge of high pressure aloft.

The upper-level map (500 hPa pressure, about 18,000 ft) on Sunday evening shows the situation (see below).

The difference from normal of 500 hPa heights (or pressure) for the last week was way above normal  (see below, red indicates strong ridging...which is the same as high pressure aloft).

Translation:  the high-pressure aloft was very strong and persistent.

In the summer, such a pattern would give us a heat wave.

But in winter we get a cold wave!  But why?

High pressure is associated with sinking air aloft, which kills middle and upper-level clouds.

Without clouds, the Earth can effectively emit infrared radiation into space.  There are no clouds to get in the way!  Nights are very long and the sun is wimpy, so solar heating is weak.

The ground cools more effectively than the atmosphere aloft and this helps create an inversion, with temperature WARMING with height.   The inversion is also strengthened by the high-pressure aloft, whose sinking motion warms the air aloft (air warms as it sinks due to compression by the higher pressure at lower levels).

The inversion is a very stable feature and prevents the mixing of air at lower elevations.   It protects the low-level cold air from mixing out.

Want to see the inversion?  Here is a plot of temperature (red) and dew point on the Washington coast at Quillayute on Tuesday morning.  Temperature is increasing with height at low levels.  An inversion!

Each day the air got colder near the surface.  Cold air can hold less water vapor than warm air.  Water vapor starts to condense out into low clouds and fog.

And it is even worse than that.  The top of the clouds reflect solar radiation back to space, enhancing cooling.  Clouds are good emitters of infrared radiation.  More cooling.   Low clouds are cooling machines!

So if you want to blame the cold, cloudy weather on something, blame the high pressure!

We escape this run-away cooling in the summer because of the far stronger solar radiation, which is able to heat the surface and destroy the low-level inversion.

November 27, 2023

Are King Tides a Threat During the Next Two Months?

A number of media stories have been talking about King Tides and flooding during the past few days, and I have gotten several emails from worried readers.

So let's talk about the reason for King Tides and evaluate the threat.

The highest tides of the year...the King Tides... typically occur this time of the year for two reasons.

First, the astronomical setup is ideal, because the Earth is closest to the sun around the New Year.

Second, this is the stormest time of the year, with Pacific cyclones associated with low pressure, and low pressure causes the water level to rise.

Monthly high tides, also known as spring tides, occur twice each month when the sun, moon, and earth are aligned.

And this alignment is enhanced during the winter because the Earth is closer to the sun during our cold period.  Believe it or not, the Earth is nearest to the sun during our winter!  (see below).  Thus, the gravitational attraction of the sun is larger during winter, which produces a greater maximum daily tide:  the KING TIDE.

Finally,  regional low pressure increases the water level.  

How much?  When sea level pressure falls by 1 hPa (or 1 mb), the water level rises by about 1 cm.   So a deep storm that causes pressure to fall by 25 hPa can result in a water rise of around 25 cm or roughly 10 inches.

Now let's look ahead.

Take a look at the predicted astronomical tide levels for November, December, and January below (the green line is today).  For November, tides will max out during the next few days around 12.5 ft above Mean Lower Low Water (MLLW), the average level of the lowest tide for each day computed over a 19-year period.

December will have a number of days (mainly during the middle and end of the month) that will get to the same level.    Mini-King tides.

Mid-January will bring max tides that are a bit higher...around 13 that will be the time of greatest vulnerability.

There will be little problem of high tides and flooding without a strong low-pressure system moving we need to watch the forecasts for the next few months.   Right now pressure is well above normal...and will remain that way for several days.

Beyond, 10 days the forecasts have little we are going to have to wait and see.

Want to know about the forecast pressure for the next week?  Check out the ensemble of many forecasts below for Seattle's sea level pressure.  Forecast uncertainty gets very large after December 2 (the forecasts are not in agreement).

The latest model run has a decent storm on December 3 (see sea level pressure forecast below) with a deep low-pressure center heading into Washington State.  Fortunately, the astronomical tides will be low then.


November 25, 2023

The Remarkable Life of Steve Pool

I am very sad to report the passing of Steve Pool, past chief meteorologist at KOMO TV, and a dear friend for many decades.

Steve was one of the most exceptional and generous individuals I have ever known.

A brilliant communicator.  A kind and generous soul.  A highly intuitive and insightful meteorologist. And someone who gave so much to our community.

I first got to know Steve during the mid-80s, when I got a call from KOMO-TV asking whether I would instruct him in meteorology; he had just taken on weather responsibilities at the station.   

For the next year and a half, Steve and I worked together intensively to cover the essentials of meteorology, Northwest weather, and weather forecasting.  An extraordinarily bright guy, Steve quickly mastered a huge volume of weather knowledge and became a very able local weather analyst and forecaster.   He was determined to get his forecasts right, and we would often talk during the late evening before his 11 PM broadcast.

As I got to know him better it became clear to me that he was a preternaturally talented communicator and that I had a lot to learn from him in that domain.  

And I mean much more than a smooth delivery.  He had the ability to connect with people.  A disarming smile, great empathy, and a personality that was upbeat and sunny.  I don't think I ever heard him talk ill of another.

We would regularly talk about difficult forecasting situations, driven by his strong 
commitment to not only get the forecast right but to get the explanation correct.

But Steve had many other dimensions and none were as noteworthy as his dedication to the community. 

One day he called me, suggesting that some UW students could intern at KOMO. This 
internship was a great success, giving roughly 3-4 students a year a chance to 
assist in developing the daily weather offerings at KOMO, including the use of a complex 
graphics system, preparing forecasts, and even practicing in front of the camera. All under the 
eyes and with the assistance of a master weathercaster. 

Many of Steve's student interns went on to successful careers as TV meteorologists, including Shannon O'Donnel, M. J. McDermott,  Kelley Bayern, Nathan Santo Domingo, Jefferson Davison, Scott Sistek, Brandon Wholey and Matt Leach--to name just a few.  Scott  Sistek worked for Steve for 20 years and together they wrote an excellent, conversational book on Northwest weather that received an impressive 5-star rating--Somewhere I Was Right.

Shannon O'Donnell, a past intern, is now chief meteorologist for KOMO.  And in Steve's 
tradition, she is teaching a course in my department on weather communication,  including a Dawgcast available online to the general public. 

Steve's influence will be very, very long-lived.

Steve was extremely interested in outreach to young people, and a good example of his efforts 
was the annual Weather Education Day at Safeco Field. Before the game, THOUSANDS of 
students would enjoy learning about basic weather principles and local weather, presented by 
Steve and his guests (I even did it one time).

Steve became a mega-local celebrity, but this did not change him, and he used that celebrity 
to assist in fun raisers and other gatherings for local charitable organizations and importantly 
for his alma mater, the University of Washington. He helped raise millions of dollars for a 
whole slew of important causes and was the MC for many public events put on by my 
department.  On the side, Steve built a small enterprise, assisting folks in learning how to be accomplished communicators.

Shannon O'Donnell, myself, Steve, and Scott Sistek

Steve loved his family, always talking about his wife Michelle and their talented daughters,
Lindsey and Marissa.  When I went over to his house he talked with great pride of his father, who served in WWII  and was shot by the Germans in northern France after D-Day. Steve was a history buff and had a whole wall of history books in his study, as well as the many Emmys he had won over the years.

But what impressed me more than all his accomplishments was his sheer bravery when his health failed.   I don't want to say any more about it, except that he stayed positive and hopeful to the end, where many would have surrendered to despair.  

An extraordinary human being that has given so much, to so many.  An individual who has profoundly changed our lives in so many positive ways.  He will be missed.

The Darkness

 It has been often said that it is darkest before the dawn. Well folks, we have been very dark and dawn is a long way off. The image from th...