Super Convergence Zone

 If you ask any Western Washington meteorologist about the most important local weather phenomenon, the answer is immediate:  the Puget Sound Convergence Zone.

Today, we had a spectacular example....let me show you.

For those of you who are unfamiliar with this feature, such convergence zones occur when the low-level winds on the coast are westerly or northwesterly (from the west to northwest). 

 The air is deflected around the Olympics and then convergences somewhere over Puget Sound (see figure below).    Converging air at low levels forces upward motion, resulting in clouds and prediction.  

A convergence zone is born!

We typically get 10-20 convergence zones per year, with the greatest frequency from March through June.

A strong convergence zone occurred this afternoon, with associated heavy rain quite evident on the weather radar around 3 PM (see below).    You see the east-west precipitation band (yellow and green colors)/   That is the convergence zone, which extends into the western foothills of the Cascades.

 

The satellite image at the same times shows the cloud band and a clear zone to the south....we often see this.   It can be pouring over the city, but clear and sunny to the south.

If the air is relatively unstable (prone to cumulus and cumulonimbus clouds caused by temperatures declining rapidly with height), convergence zones can produce lightning and thunder. Many convergence zones often produce a single lightning flash and today's event was no different.

The location of the flash is shown below (again, about 3 PM).  We call this a "one-flash wonder"

Rain was heavy in the convergence zone and nearly absent to the north and south.  To prove this, below is the 6-h precipitation total ending at 5 PM.  Around a half-inch in the convergence zone but nearly nothing to the north and south.

When I was a graduate student many years ago, the origin of the convergence zone was not known.  Weather Service forecasters thought there was a strong band of rain offshore that sometimes moved in off the ocean and then took up housekeeping over the central Sound.

Today we understand the critical role of terrain and particularly the Olympics.

But there is something else that changed:  the ability of high-resolution models to predict convergence zone precipitation well in advance.  For example, below is the predicted  3-h precipitation ending at 5 PM on Monday.   

When it is sufficiently cold the convergence zone can produce a very well-defined band of snow across Puget Sound, something that happened in 1990.   Even yesterday, there was convergence zone snow above approximately 750 ft ASL.   Here is a picture sent to me by Dr. Peter Benda at around 1200 ft in the hills above Bellevue (3 inches of snow!).

Under very rare conditions, the snow band can get very, very narrow 😈

Can We Deal with the Snoqualmie Pass Snow Closures Better?

Late Thursday afternoon, moderate snow led to multiple crashes and trucks/cars sliding off I-90.   As a result, the pass was closed for several hours, allowing the removal of vehicles and letting the WSDOT plows improve the drivability of the roadway.

Now, here is my frustration.    

The snow was foreseeable.  Weather information is so good now that we can warn folks in real time of the approaching snow band so that they can slow down!

The key modeling tool is the NOAA/NWS HRRR model, which runs at high resolution EVERY HOUR.  

The 11-h snow forecast for 3-4 PM snow below.  Snow around the pass!

The 12-h snow forecast for 4-5 PM is here.  Slippery conditions!

You get the idea....snow was predicted on the western side of the Cascades and the Cascade passes well ahead of time.

In real time, the weather radar showed the snow falling at 4:30 PM.

A few years ago, I offered to build a system for WSDOT that would provide state-of-the-art prediction of snow in the pass with real-time updates provided by weather radar, satellite imagery, and other weather assets.  

This real-time snow guidance could be used to update reader boards on the side of the highway.

The goal was to stop the snow closures and keep folks safe.  Unfortunately, they were not interested.

Another example of valuable information available from meteorologists not being used effectively by society.

Will You See the Total Lunar Eclipse Tonight?

 Maybe.

Tonight around midnight our time, the moon will be entirely in the earth's shadow. 

 A total lunar eclipse.  During such periods, the moon often develops a red color, sometimes leading to the name "blood moon."

The big issue tonight will be clouds.....but don't give up yet!

The visible satellite image right before sunset shows the problem (see below).   Unstable air with a lot of cumulus clouds moving into western Washington.  Solid clouds on the western slopes and crests of the Cascades and Olympics.

But hope is not lost.  There is a large clear zone east of the Cascades, and over the western lowlands, the cumulus clouds are scattered and MOVE, and thus the moon will come in and out.

The radar image at the same time shows the situation well.

What will things be like during the eclipse?  The timing is shown below.  The total eclipse will be from roughly 11:30 PM to 12:30 AM.

The cloud forecast of the UW WRF model for midnight suggests that some of you...even in the west, will see it! 

I know I will be looking.....I love eclipses!

Finally, why does the moon look red during total eclipses? 

The same reason the sun looks red when setting:  light from the sun has to go through a lot of the atmosphere. Blue and green colors are scattered more than reds by atmospheric molecules.  So those colors are lost, leaving the longer-wavelength reds.

A Very Wet Period Ahead

Atmospheric rivers can be things of beauty, and the atmospheric river coming in on Sunday will turn heads.

The map below shows the total amount of water in a column of air (the precipitable water) at that time and you can see a "river" of higher amounts of water content streaming northeastward towards the Oregon/Washington border (greens and yellows are the highest amounts).

This is an atmospheric river, and since it starts just north of Hawaii, you might even call it a Pineapple Express.

This particular river is associated with strong southwesterly winds between a low over the Gulf of Alaska and a high off over California.  The typical setup for such moist plumes.

The total precipitation predicted through Monday morning is impressive, with nearly 3 inches in Seattle and twice that in the mountains to the south.  Most of the precipitation will fall on Sunday as the atmospheric river reaches our region.

Several of you have emailed me asking about snow.   Well, I have some good news!  Up to two YARDS of snow are predicted in some of our regional mountains  during this event (see below).

It is also important to keep in mind that rain and snow in mid-March is golden.... much more valuable than early in the season.    

All this water will be stored in reservoirs (no need to worry about leaving space for later flood control) and snowpack, and this water will moisten the soil immediately before we start to dry out in spring.

Seattle's reservoir storage is actually above normal now (see below), and the heavy rain is well-positioned to help boost the Yakima drainage.

All in all, an encouraging trend.

Also encouraging is the substantial rehiring of many of the probationary staff at NOAA.  Critical buildings will not be sold.  There will be more on this in a future blog.

Not so encouraging.   Will you be able to see the total lunar eclipse on Thursday night (around 10 PM)?

 Here is the cloud prediction for 11 PM on Thursday.  

Better go to eastern WA if you want a sure view!  NW Washington a possibility.

Should California Ship Water to the Pacific Northwest?

President Trump has suggested that water be transported from the Pacific Northwest to California to help fight fires and for agricultural use.

This idea was strongly criticized by many, including the authoritative Seattle Times ClimateLab, which is supported by disinterested, civic-minded advocacy groups and individuals (see below).

But perhaps, examining the weather situation this year, President Trump's error was not in the general idea, but in the direction of water flow.  

Specifically, California should consider sending water to the Pacific Northwest, particularly this year.

To illustrate, below is the latest 180-hour forecast precipitation accumulation over the western U.S.  

The mountains of northern California and the Sierra Nevada will receive at least twice what will fall on the Cascades and Olympics. 

Los Angeles, yes, LA... will get about the same precipitation amount as Seattle.

Do you want to be shocked?    If so, look at the forecast precipitation during the next week at Blue Canyon Airport on the western slope of the Sierra Nevada (just northwest of Lake Tahoe).  The high-resolution US GFS model is going for about 50 inches of snow!

This pattern has happened again and again this winter.   As a result, the reservoirs in California are above average, with some close to being full, EVEN BEFORE the massive CA snowpack starts to melt.

Contrast California's wet bounty with the current situation of the Yakima drainage, which is currently well below normal (see below).

Now that I have convinced many of you of the necessity of shipping water north from sodden northern California to the parched Pacific Northwest, is this idea practical?

It may be! 

Far easier than the famous water works of southern California, in which water from the Owens Valley was shipped hundreds of miles to LA across formidable terrain.

Using Google Maps,  it only took me seconds to find a nice route from the wet northern CA mountains to the dry domain of Yakima and eastern WA.  I am sure many of you could do better.

Mostly level or downhill...and I have hardly optimized the route!

In short, out-of-the-box thinking is needed to allow the West Coast to deal with the frequent north-south imbalances in precipitation.  Northern CA water is not fated to only go south.  In many ways, going north is more practical.

The Sun is Back!

For those who suffer from seasonal affective disorder or a bit of dark-day low spirits, this is a special time of the year.   

Relief is on the way!  The sun is coming back...very quickly.

Consider the solar radiation reaching the surface in Seattle over the past year (below).  

It was pretty depressing near the turn of the year, with values consistently below 5 (megajoules per square meter, if you want to know the units).  But during the last few days we have received almost three times as much!

The length of day has also gotten longer...much longer, something shown graphically by the "Sun Graph" for Seattle (below)

This figure shows the length of day, with the light blue color indicating the period between morning and evening civil twilights.   We have gained several hours of light compared to the depth of winter and are now in the period when the length of day is increasing most rapidly.

Feels very good.

For a meteorologist like myself, the return of the sun has implications far beyond its pleasant feel on the skin.

The increasing solar radiation results in the warming of the surface, while the atmosphere above remains quite cool.

The result is that temperature change with height, the cooling with height, becomes very large this time of the year...and that has big implications.

A large temperature decline with height (also called a large lapse rate) results in the atmosphere becoming unstable and convecting, not unlike the situation in a lava lamp that is heated from below (see example below).

In the atmosphere, such instability leads to fields of cumulus clouds, such as shown below.

Today, large fields of sun-driven cumulus clouds were observed all over Washington State (below). 

 You see all the little white dots over land across the western side of the Olympic Peninsula?  Or the little white specks southwest of Spokane?  Lots of cumulus clouds.

 Blame the warming effects of the incipient sun of spring.

Will the Key Weather and Climate Facility in the United State be Sold Off?

 There are many media stories circulating today stating that the key U.S. weather and climate facility in the U.S. is going to be sold off:  The NOAA Center for Weather and Climate Prediction.

This location houses many of the key groups overseeing U.S. weather and climate prediction.  I have attended meetings in the facility or met with NOAA/NWS scientists there literally dozens of times.

Selling off this building and dispersing the groups housed there would be a death blow to US environmental prediction capabilities.

The question: Is there any truth to this?  Certainly, this story has been distributed through dozens of major and minor media outlets.   But as you know from my previous blogs, I am not a little cynical about the "facts" found in many media outlets--so let's check it out.

This story originated from two sources.  One is a story in Axios (see below).

The second was in The Verge, a technology website.

Neither of these websites can point to any official statement or documents to support these claims, just unnamed "sources."

I went to governmental websites, such as the DOGE lease cancelation list (see below).  No mention of the NOAA Prediction Center. None.

Checked the GSA website.  The NOAA facility is not on it.

The NOAA Prediction Center was a custom-built building designed for the important role it is now playing.  To sell it off would be a catastrophic error, with profound impacts on weather and climate prediction in the U.S.

There is no sign of any official intent to sell the building, and I suspect the stories noted above are not correct.

NOAA plays a crucial role in collecting weather and climate data,  ocean and atmospheric research, and predicting weather and ocean conditions.   Although essential, NOAA needs reform, particularly in dealing with an ineffective bureaucracy and loss of innovation.

When will DOGE and the new administration talk to the atmospheric and ocean community to learn about these problems and how to correct them?

With reform and rational change, U.S. weather and environmental prediction could be substantially improved.

A Very Wet California

 If you are wondering where much of our precipitation will be headed, look to the south.  California is going to be very wet during the next week or so.

Below is the predicted total precipitation through March 18, using the European Center model.  As much as 12 inches over portions of Northern CA.    Even LA gets fairly wet.

Seattle will be drier than LA...think about that.

Why is this happening?  

Because one after another, upper-level troughs of low pressure will plunge southward into California, leaving Washington State relatively high and dry.  Troughs are associated with upward motion and precipitation.

Let me show you a series of upper-level charts that present the heights of the 500 hPa pressure surface.  You can think of this as the pressure around 18,000 ft.  Blue and white colors indicate below-normal pressures...or troughs.

At 4 AM this morning, a trough was over southern CA.

Three days later (Thursday at 4 AM), another trough is over California.

Sunday night at 11 PM, ANOTHER trough is digging down over California.

Next Thursday morning at 11 AM, another trough is pushing into California.

You won't believe this.. on Friday night, one more trough moves into California.

This kind of pattern has dominated much of this winter.

Why?  As far as I know, there is no clear answer, but something is forcing this persistent troughing over the Golden State.

With all the troughing action over CA, reservoir levels are quite high throughout the state.   

But there is a major concern.  Substantial late winter precipitation leads to bountiful growth of chaparral vegetation, which can enhance the potential for wildfire later in the year.   The past few years have had wet winters, which contributed to the huge fires around Los Angeles.

UFO Clouds

 I received a half-dozen emails this week about some strange clouds visible on Wednesday. 

  A few asked (perhaps in jest) whether they were connected to UFOs or some paranormal phenomena.

Picture by James Robers

Picture by Kathleen Millen

They are not natural.  Something artificial caused these strange cloud holes.

Aircraft.

These features have several names:  hole-punch clouds, fallstreak holes, and punch hole clouds are some examples.

They are generally associated with a middle-level cloud deck, such as an altocumulus layer, in which the clouds are supercooled, which means liquid water clouds below freezing. 

 Typically, supercooled cloud water can occur when the air temperature is between 0C and -15C (32F to 5F).

Here is a satellite picture around the same time as the first picture was taken....you can see the extensive cloud layer.

It is fascinating that clouds can be made of liquid water that is below freezing.  

However, things can change fast if such a cloud deck is disturbed by an aircraft that is either ascending or descending through it. Such aircraft passages can cause some of the supercooled liquid water to freeze.  How?

One way is that the wings can cause pressure to fall, and that leads to cooling, cooling the air enough so that the water freezes.

Once one gets some ice, water vapor rapidly moves to the ice crystals causing them to grow and fall out.

This is a very fast process that quickly causes the liquid water droplets to evaporate and ice crystals to fall out.

A cloud hole is born!

You can often see the ice crystals falling out, and that is why they are called fallstreaks.

Don't like this explanation.  Don't worry....there is another one.....