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.....

NOAA Personnel Cuts Are A Mistake and Must Be Reversed

When a tree is badly overgrown and in danger of falling over, does a tree surgeon simply lop off the new growth and walk away?

No.  The tree expert examines the tree holistically, determining the alterations required to ensure its health and longevity.  Importantly, the tree surgeon determines which healthy sections should be left alone.

NOAA and Federal agencies dealing with weather and climate are no different. 

They provide functions acutely needed by the American people.  But, without proper management for too many years, problems have developed.  Reforms are needed.  Some programs should be enhanced, some left alone, and others ended.

Like an expert tree surgeon, the administration needs a deep understanding of the entity it wishes to improve before taking action.  

Unfortunately, the current administration has not done this, deciding to simply cut the recent growth (new employees) irrespective of whether their roles are important or critical. 

This is a mistake that may undermine the U.S. government's ability to provide critical weather and climate services to the nation.

Seattle NWS Office

Yesterday, hundreds of NOAA employees, including many in the National Weather Service, were told their positions were ending.  Nearly all were probationary employees, generally those hired during the last year.  Some are in essential jobs.

Local National Weather Service Offices play a key role by providing weather forecast services to local communities.  Most of these offices are understaffed at this time, some seriously so, because of poor management decisions by NOAA/NWS administrators.

By firing dozens of new weather forecasters and support staff, some offices will no longer be fully functional; all offices will be degraded.

There is little doubt that many Federal agencies have been increasingly ineffective and wasteful of resources.   This is certainly true of NOAA, and I have written several papers on this subject and testified in Congress on the issue.  

Members of both parties know about NOAA's problems.   For example, 15 years ago, many of us in the Northwest weather community made the case that our region acutely needed a coastal weather radar.  NOAA management was not interested.  Senator Maria Cantwell had to intervene and force them to do it.  

NOAA has fallen WAY behind in critical technologies such as numerical weather prediction and machine learning.   Its local forecasts are generally inferior to those provided in the private sector.  Its computer resources are inadequate for its mission.  Its bureaucratic structures are often duplicative and ineffective.   NOAA has often rejected working cooperatively with others, such as the academic community.

I am only warming up on its problems😀.

But despite its deficiencies, NOAA does have strengths in many areas, such as atmospheric and ocean observations.  Thunderstorm and severe storm prediction.  Hurricane warning and forecasting.    Its role is still essential.

The simplistic, mindless cutting of new employees is not the way to deal with NOAA's problems.   

Instead, the new administration needs to gather a group of topical experts and users to identify the problems and to propose cost-effective solutions.   Importantly, it needs to immediately reverse the position terminations until a rational, fact-based plan is ready.

We can have a more effective NOAA and probably spend less money, but this can only be done with knowledge of its strengths, weaknesses, and potential.    

NOAA Weather Satellite

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Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters. I will talk about the extended spring forecast and new AI forecasting technology.

Late Winter Heat Wave With a Twist

 It felt like spring today in western Oregon and Washington, with some temperatures soaring into the 60s.

The high-temperature map for today (Wednesday) reveals low 60s east of Puget Sound and along the Washington coast and UPPER 60s along the Oregon coast.   In contrast, eastern Washington and Oregon were much cooler, with temperatures stuck mainly in the low to mid-50s. Even some 30s on the eastern slopes of the Cascades.

A close-in view around Puget Sound shows the contrasts (below), with 65F in Carnation, near the western footfills of the Cascades, but ten degrees cooler over western Seattle.

For many locations, this was the warmest day so far this winter.

So why was the coast so warm? Why so warm over the eastern suburbs of Seattle?

One can get a hint by looking at the regional sea level pressure pattern this afternoon at 2 PM (see below).  Relatively high pressure inland and lower pressure along the coast.

The pressure pattern forces easterly winds (from the east), directed from high to low pressure.

Such easterly winds remove the cooling effects of the Pacific.

It also produces downslope flow on the western side of the Cascades and coastal mountains.  This downslope flow produces localized warming as the air is compressed as it moves from lower pressure aloft to higher pressure near the surface.  Warming just like in your bicycle pump.

You can see this downslope warming effect in the temperature forecasts of the UW WRF model for 10 AM this morning/ Reds areas are the warmest temperatures.

At this time, the warmest temperatures are on the western slopes of regional terrain due to the downsloping, sinking air.  You can also see cool air (blue colors) being pushed up the eastern slopes of the Cascades.

Tomorrow should remain relatively warm over Western Washington south of Everett and over all of western Oregon but somewhat cooler along the coast as the easterly winds weaken.

Similar conditions on Friday, followed by a slow cool-down over the weekend.  Dry at least through Saturday.

Time to get the garden cleaned up or to enjoy that long-neglected outdoor recreation.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters. I will talk about the extended spring forecast and new AI forecasting technology.

The great disappearing low. Where will it go?

 The infrared satellite image tonight is impressive, with a beautiful convergence of clouds into the low center west of the Olympic Peninsula (see below).

But you have to feel sorry for this low:  it is collapsing as it approaches landfall.

All of the modeling systems agree on the collapse, but there are subtle differences model solutions.

And that will influence what happens to us.

 For example, the American GFS model at 4 PM today (Monday) showed a potent low center of 972 hPa central pressure:

But my 7 AM Tuesday it was a wimpy 1003 hPa.   Sad.

The NOAA HRRR model forecast for the same time (7AM) is about 1000 hPa and the low center is a bit further to the west:

While the UW WRF model has a 999 hPa low a little further to the east.

Finally, the uber-accurate European Center model drops the low to about 1000 hPa and takes it over Sequim.

You would think that such a disappearing low would not produce any winds of note over western Washington.  

But yet Seattle WindWatch, which presents a whole range of forecasts, is still going for decent winds over Seattle (see below, these are the strong winds ANYWHERE in the City, even close to the water).  Gusts to 30-40 mph are found in many models, with some going into the 40s.  

One thing that is helping maintain the winds is that there is relatively high pressure to the south so that even a poor excuse for a low can produce a large north-south pressure difference and strong winds.

But like the late-night commercial...there is more!   

As the low passes to the north, winds from the west will hit the Olympics and they descend on the NE side of the barrier.  As the air sinks, it warms by compression, which causes pressure to fall (warm air is less dense than cold air).  

As shown in the forecast map pressure map for  7 AM, the mini-low is predicted by the UW WRF model on the NE side of the Olymics, which contributes to a locally enhanced pressure gradient (change of pressure over distance) over western Seattle and the Kitsap area. 

A wind boost due to the terrain.

This kind of situation on steroids occurred in 1979 during the Hood Canal Storm, when a mini-low formed south of Port Townsend, resulting in winds reaching 100 mph (see below).  

Washington State residents had a very expensive bridge replacement after that.

Will there be a big windstorm tomorrow night?

 Update Tonight

There is an interesting ultra-local potential twist to this event.... a Hood Canal twist.   The storm is going to rapidly weaken and staff as it makes landfall, with it exact location making a big difference on the localized winds.

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I have gotten over a dozen emails asking about a potential storm.  The amateur sites are going into overdrive talking about the birth of a "monster storm" and other over-the-top descriptions.

So let's examine what the latest model simulations are predicting.

Before I do that, let me note that it was quite windy during the last several hours as a strong trough of low pressure moved through, creating a large north-south pressure difference over western Washington (see model forecast for 7 PM).  The solid lines are isobars of constant sea-level pressure.

This large pressure change produced some serious wind gusts (see max wind today below), reaching an impressive 63 mph at Paine Field in Everett.   Several thousand customers have lost power.

This is an appetizer for the meteorological buffet tomorrow.

Let me show you a series of forecast maps of sea level pressure for tomorrow.  We are close enough in time that this forecast should be reliable.

At 1 PM, an impressive-looking low center, with a central pressure of 982 hPa, is found west of northern Oregon.  For some perspective, this is not even close to the central pressure of the "bomb" cyclone in November (which got down to around 940 hPa).

By 10 PM tomorrow (Monday) night, the low has weakened slightly (to 987 hPa) and has moved towards the central Washington coast.    Very strong pressure difference (and thus winds) along the Oregon coast.

By 4 AM Tuesday, the low has weakened to 996 hPa and is crossing the Olympic Peninsula.

By 7 AM Tuesday, the low had weakened to 1002 hPa and located near Everett.

At 1 PM Tuesday, the low had greatly weakened and was now in NE Washington.

If this forecast is correct, Puget Sound will not see a major blow.  

One thing I have learned about such events is that rapidly weakening lows are rarely big wind producers.  Also, the trajectory of the low is not optimal for strong winds over Puget Sound and NW Washington.  Too far south.

Looking at the highest winds predicted during this event (below), the northern Oregon coast looks like the place to be for a strong blow, with gusts reaching 65 kt.   It's not so exciting over the western WA interior.  Gusts to 30-40 mph perhaps.

But a good forecaster never forgets about uncertainty and the forecast of this storm has varied quite a bit over the past several days.   One way to explore this uncertainty is by looking at ensembles of many forecasts.  

For example, the ensemble of many forecasts for wind at Seattle indicates that most of the solutions are for only modest sustained winds of about 15 kt (12Z/25 is 4 AM on Tuesday, the black line is the average of many forecasts, and winds are at the surface in knots)

In any case, there will be plenty of precipitation, which our region needs.

Why do Atmospheric Rivers Occur?

A significant atmospheric river event will occur tomorrow (Sunday) and Monday, with heavy precipitation in the mountains and South Sound.

The latest UW WRF model forecast predicts up to 10 inches in the Cascades, with the southern WA Cascades being hit the hardest (see below).   In contrast, a profound rain shadow will extend from the NE Olympics to Bellingham. 

It is now clear that there will be some serious flooding in some locations. For example, the NOAA/NWS River Forecast Center is forecasting major flooding on the Snoqualmie River near Carnation.   

Want to see something spectacular?   Go to Snoqualmie Falls on Monday.  If you can get there.😁

Atmospheric rivers in our region are associated with plumes of warm, moist air from the south, southwest, and west.

NOAA weather satellites can sense the water vapor, which is very evident in the water vapor image from this morning (below).  A massive plume of water vapor is moving our way.

 

Numerical weather prediction models, like the UW WRF model, can skillfully forecast such water vapor plumes, which release massive amounts of water as the air is forced to rise by our region's substantial terrain.

Meteorologists favorite diagnostic for atmospheric rivers is integrated water vapor transport (IVT), which is the amount of water vapor times the wind speed, summed up in the vertical (that is where the integrated comes from).   This quantity is more closely related to the potential for regional rainfall.

The prediction of IVT for Sunday morning is shown below, with the arrows showing both the direction and magnitude of the moisture transport   Large values, but not record-breaking by any means.  

Such moisture plumes are generally warm as well.   In fact, to get large values they HAVE to be warm since the amount of moisture air can hold depends on temperature (warm air can potentially hold more water vapor than cold air).

Atmospheric rivers form in our region when strong southwesterly atmospheric wind currents occur, currents that move large values of water vapor out of the subtropics.

The atmospheric flow pattern that does this is usually characterized by a strong low-pressure area in the Gulf of Alaska and higher pressure west of southern California.

Not surprisingly, this is exactly the pattern forecast for Sunday morning at 10 AM for a level around 5000 ft  (below).  With high pressure to the south and low pressure to the northwest, a strong pressure/height change is created, which produces a strong southwesterly flow. 

The interesting thing about atmospheric rivers is that they are like regular rivers in another way...not only does water come into the river at the beginning, but there is a convergence of water vapor from the sides along the way, not unlike the small streams that drain into a river over its entire path.

 

Heavy Rain Coming This Weekend

Our dry period is about to end dramatically.

Several plumes of moisture... popularly known as atmospheric rivers--will make landfall on Saturday, Sunday, and Monday.

Reservoirs will get substantial inflow and several rivers will approach minor flood stage.

Consider the regional accumulated precipitation through Tuesday morning (below).

Wow.  Some parts of the Cascades and coastal mountains will get as much as ten inches of liquid water.

Zooming into Washington State, one can view the profound rain shadows downstream of the terrain.  One is located northwest of the Olympic Mountains and the other one...much larger in extent...is east of the Cascades.

Precipitation picks up again as it rises on the western slopes of the Rockies.

As noted earlier, this heavy precipitation is associated with a potent atmospheric river in which warm, moist air from the subtropics pushes northward into the region.  You can see this moisture plume on Sunday at 4 AM below, with the air coming from north of Hawaii.

Associated with this subtropical plume, the freezingly level will be as high as 9000 ft over SW Washington and 5000 ft over the north Cascades (see map below at 7AM Sunday).

With the influx of warm air, most of the precipitation below roughly 5000 ft will fall as rain and not snow during the weekend and Monday.  

The snowfall total through Tuesday morning (below) indicates that the higher elevations in the North Cascades do well with snow, but Snoqualmie Pass gets very little (mostly rain)

Finally, this pulse of precipitation, coupled with a high freezing level, will cause many regional rivers to greatly increase their flows, some to near flood level.  For example, the Snoqualmie River will rapidly surge to near flood level early next week (see below).

Anyway, this event will greatly aid in alleviating the dry conditions of the past month.