The Stratosphere Plummets over Seattle....and Huge Precipitation Contrasts

Today, the stratosphere was much, much closer to you than normal, and we all lived to tell the tale.

As many of you know, the lowest layer of the atmosphere is the troposphere, where nearly all the weather occurs (see below).  Temperature generally decreases with height in the troposphere (red line)

Above the troposphere, there is the stratosphere, where the temperature increases with height...first slowly, then rapidly.

Temperatures are warm near the surface due to the heating of the surface by the Sun, while aloft the heating is due to the absorption of ultraviolet radiation by the ozone layer.

Over our region, the boundary between the troposphere and stratosphere (the tropopause) is typically around 35,000 ft... just a little above the typical cruising altitude of jet aircraft.

You can often see the boundary from your aircraft window.   Clouds and haze in the troposphere, clear air and blue skies in the stratosphere (see below)

Something dramatic happened this morning to the boundary between the two layers (again, the tropopause).

It plummeted from roughly 35,000 ft to around 23,000 ft.  

If you were flying above western Washington this morning at typical cruise altitude, you were deep into the stratosphere, with lots of ozone being ingested into the aircraft.

How do I know the stratosphere was that low?   

Because there was an ascent of a National Weather Service radiosonde (balloon-lifted weather instrument) that showed the situation clearly.

Here is the plot, with red being temperature and blue dew point.  Temperature stopped cooling, and air became very dry (indicated by the dew point declining rapidly) around 400 hPa pressure, which is found around 23,000 ft.

Weather forecast models create a map of the height of the tropopause, and one was shown before 5 AM this morning.    

It is very high over the warm tropics and lower near the poles.  

But there are also complex distortions in the height of the stratosphere over the midlatitudes and polar regions, and one such structure was over our coast, with the blue color indicating a downward distortion of the tropopause.

Weather balloon went right into this.

This local distortion of the tropopause was due to a well-defined upper-level trough this morning, indicated by the blue colors and the low "L" in the figure below

How unusual was the descent of the stratosphere to 23,000 ft this morning?   I checked the radioaodne data for the last 50 years.   

It was the tenth-lowest excursion in October on record.

Impressive.

Finally, since I am talking about impressive things, how about the total precipitation around the Olympics over the past 48 hours (below)?

Nearly five inches on the southeast side and 0.17 inches on the northern flank near Port Angeles. 

We are talking about a factor of over 25 times!  

Why did this occur?  

With the low offshore, strong moist winds approached the Olympics from the southwest and were forced to rise, releasing a large amount of moisture as rain.  

On the northern side, the air sank, was warmed by compression, and the relative humidity dropped, killing any precipitation.

You got to love living here... 👴

Godzilla-Low Pressure, Heavy Rain, and Drifting Snow Ahead for the Pacific Northwest

Northwest meteorological winter is about to begin dramatically.    

Heavy rain and massive mountain snows are on the way.  Reservoirs will begin to fill.

Those worried about El Nino drought will be able to relax.  

The forecast from the NOAA global model (the GFS) for the next week predicts a stunning persistent upper-level low along our coast, illustrated below by the average 500 hPa heights (think of it as pressure at 18,000 ft) through next Saturday. 

Blue colors indicate the deep low, which will bring showers and cool temperatures to our region.

But now prepare yourself.  

Below is the forecast for the subsequent 7 days. 

Mamma Mia!  

An intense upper-level low over the northern Gulf of Alaska.  The PERFECT configuration to moisten our region.

Consider the total precipitation predicted over the next two weeks by the NOAA model is shown below.

 Unbelievable. Massive amounts, with over ten inches of liquid water in some mountain locations.  Way more than normal for the period.

Snowfall in the mountains will be extreme.   Not feet. Yards of snow at some elevations.

I know what you are saying.....this is the U.S. global model. What about the uber-skillful European Center AI model?

Same solution.  Very wet over the next two weeks.  Let me show you.

First, the total precipitation for the same period.   Huge amounts in the mountains. 

And like the NOAA forecast model, bountiful snow.

I noted in earlier blogs that extreme El Nino years often enjoy good water resources in the Northwest.   No drought. The next two weeks may be the start of this favorable outcome.

How Unusual Has Been the Temperature and Precipitation this Fall?

 Several folks have asked about this autumn.  Has it been drier and warmer than normal?

Let's check it out by considering a representative location:  Olympia.

Below is a plot of cumulative precipitation at this location from September 1 to yesterday.  Green is this year, and the brown line is normal (the climatological values).

September was close to normal, but October has been quite dry.

No wonder I have been able to bike to work without rain gear!

Temperature is shown below, with the blue bar showing the daily highs and lows and the brown band showing the normal range.  Red indicates record highs.  

September was very close to normal, and October has been modestly above normal.

But let's get a better historical picture.  

Below is a plot of the Sept 1-October 21 precipitation totals for the past 50 years at Olympia.  A trend line for the period is also shown.

This year's precipitation is low, but many years were lower

Interestingly, precipitation increased over the period, so you can't blame climate change!

The average temperature for the entire (Sept 1-Oct 21) period was very close to normal ( this year was the 25th warmest year out of 50 years).

However, this is evidence of long-term warming, with about a 2°F warming over the past 50 years, very consistent with warming found in many studies.

What about the outlook for the rest of the month?  

The excellent European center model is predicting cooler-than-normal conditions (blue) over much of the Northwest (except for NE Washington).

In contrast, the European center model is going for drier-than-normal conditions over the Cascades and Olympics over the next week.

Biking should be relatively dry for the remainder of the month.

Important Milestone: The Current El Nino Has Hit Its Peak Early

The very strong El Nino appears to have hit its peak earlier than predicted a few months ago, suggesting a substantial weakening later this autumn and winter.

Let's begin by looking at the sea surface temperature differences from normal (called anomalies) for two critically important areas in the central tropical Pacific:  the Nino 3.4 and 4 areas (see map below).

The magnitude of El Nino events is usually judged by the sea surface temperature anomaly in the Nino 3.4 area... and I show the latest values below (from NOAA Climate Prediction Center).  The magnitude of this El Nino appears to have leveled off over the last few weeks, around 2.5 °C above normal.

The fact that the sea surface temperatures are pretty much unchanged during the past few weeks is illustrated by the sea surface temperature anomalies on October 1 and October 19 (see below).

Hardly changed.

 

To understand the future of an El Niño event, it is useful to look at the upstream region (Nino 4) to gain insight into the future evolution of temperature in the Nino 3.4 region during subsequent months.

Why look upstream?   Because the sea surface warming tends to move eastward with the Kelvin waves I described in my previous blog.

The Nino 4 temperature anomalies (from climatological conditions) are shown below.   The Nino 4 temperatures rose rapidly from April to late June and then declined rapidly in July and August.

This is consistent with the rapid rise in Nino 3.4 temperature a few months later, from July through September.

NOAA runs complex atmosphere/ocean models for seasonal prediction.  NOAA's primary model  (the CFSv2) is predicting a rapid decline in the temperature in the Nino 3.4 area starting right now!   

If that prediction is correct, it means we are now at the El Nino peak.

Other modeling systems are less rapid in the decline, such as the GFDL Spear system (see below), but all suggest we are near the maximum. 

In summary, it appears that we are now at the peak of the current El Nino, and the latest forecasts are suggesting a fairly rapid decline.   

However, there is a lot of uncertainty in such forecasts because of the highly convective (e.g., thunderstorm) nature of tropical meteorology, and because the interaction between the ocean and atmosphere is often poorly modeled.

Lots to keep graduate students busy over the next decade!

The implications of the upcoming decline in El Nino will be the topic of a future blog.

El Nino, Sea Level, and Kelvin Waves

The media recently reported on oceanic Kelvin waves and their connection to El Niño. See samples below.    

Some of the information is correct; some is problematic or exaggerated (samples below).

So, what are the actual facts, and why should you care?  

The U.S. has satellites in orbit that can monitor the height of sea level around the world. 

Here is the sea level elevation on April 1, before the current El Niño really got going.  

I am showing the difference from normal (the anomaly in meters), with red being higher and blue being lower than normal.   Things were pretty normal (yellows and light blue) at this time

Compare this to the situation two days ago (below).   Big rise in sea level near the equator and along the Mexican coast, with some enhancement along the Southern California coast.

Not much sea level enhancement for Northwest coastal waters (sorry, Seattle Times climate lab!)

Let's look at two West Coast sites.

At San Diego, the observed sea-level heights (red lines) are substantially higher than expected without El Nino (blue line), by roughly one foot.    This contributes to localized flooding for Southern California.

In contrast, there is virtually no enhancement along the Washington coast at Westport.  This will continue to be the case through the winter. 

So what are these Kelvin Waves that the media are headlining? 

They are an essential part of the El Niño phenomenon.  

During normal (non-El Niño or La Niña) situations, the easterly (from the east) trade winds in the tropics push warm tropical waters to the west, resulting in higher-than-normal sea level to the west (see below; red is higher than normal sea level).  The situation last winter is shown below.

Then the easterly trade winds weakened, and warm water surged east as a Kelvin Wave during this summer (see the situation in early September).  Higher than normal sea level along the equator and near the west coast of South America (dark red).

You can watch an animation of this happening below (click on the arrow).  Pretty neat!

The eastward movement of the warm water occurred in a series of distinct pulses of deepening warm water (Kelvin Waves),  with the figure below showing a cross section through one of the waves (the blue color is the warm water).

Such Kelvin waves are trapped near the equator by the Coriolis force resulting from the rotation of the Earth.

When the wave hits the west coasts of South and North America, the wave pushes poleward along the coasts, resulting in increased sea-level elevation in the coastal regions north and south of the equator.

You can see the enhanced sea level elevation along the West Coast of North America below (red is higher than normal sea level).

If you were in one of my classes, I would show a figure such as below.  

An elevated water column is centered on the equator, producing a pressure force to the north and south.  This pressure force is balanced by the Coriolis force (due to the rotation of the Earth); this balance keeps the surge in water intact.   This balance only works for water surging to the east.

That is why Kelvin waves only move in one direction (east).

Don't worry if this is a bit too much detail:  providing it for the weather nerds 😀

There is no "sloshing" back to the west when the elevated warm water hits the west coasts of North and South.  

So this is not like sloshing in a bathtub, as claimed by some media.

In any case, we are in the middle of a very strong El Niño, and strong Kelvin wave pulses of warmer water towards the east are expected.

Super Inversion

Normally, temperature decreases with height, and for good reason.  

The sun's rays warm the surface more than the atmosphere above; thus, air temperature tends to decline with elevation.

But sometimes the opposite occurs: temperatures are cool near the surface, and warm air is found aloft.

Since this is the opposite of the normal situation, we call it an inversion.

Most of the time, low-level inversions are weak, with temperatures increasing by only a few degrees above the surface before falling aloft.

This week was something else. 

 A SUPERINVERSION formed, with temperatures increasing by about 20°F within the lowest few thousand feet.

Unbelievable.

Over SeaTac Airport this morning, temperature was around 48F near the surface and around 70F at 1800 ft.   

22F warmer!  Amazing. 

At Forks, along the WA coast, temperature increased from 8 to 22°C over a similar distance in the vertical (see below), 

What is 25F!!!    Wow.

Looking at the surface weather map, showing the lowest temperature this morning around the I-90 corridor from Issaquah to North Bend, indicates a temperature range from 65 at higher elevations to 40 F at lower elevations, such as near Carnation.

Why such an amazing inversion this morning?   

The skies were generally clear, allowing the surface to cool off by emitting infrared radiation to space.  Nights are getting longer as well, allowing more time for cooling

Furthermore, there is a strong ridge of high pressure overhead (see below),

which not only produces the clear skies, but also forces sinking motion aloft that warms aloft by compression.

The inversion weakened greatly during the day as solar radiation warmed the surface.  

And with the ridge of high pressure aloft moving east, the sinking air that supports this crazy temperature structure will soon be history.

The Meteorological Cliff Ahead

We are about to descend a meteorological cliff, with little hope of return.

A transition to far cooler and wetter conditions, with no chance of reversal.

Even worse... this transition is perfectly normal for this time of the year.

Want proof?   Below are the latest temperature forecasts for several locations around our region.

In Seattle, temperatures will rise into the low 70s on Thursday and Friday before crashing down into the upper 50s next week.   And staying there.

On the coast at Hoquiaum?  Same thing.

At Snoqualmie Pass in the Cascades?    The big cooling takes them down into the 40s.

I find the October western transition in the Northwest fascinating-- and scary rapid.

Consider the climatological temperatures at Seattle (SeaTac) over the year (see below).  Red indicates the record highs, and brown shows the average temperature range (highs and lows).

Record temperatures reach into the 90s during the first half of the month, but after October 18 such warm temperatures simply don't occur.

This amazing transition around mid-October is made clearer by an expansion of the above figure for October.

Why such a rapid decline in temperatures in October?

Solar radiation reaching the surface declines rapidly during the month, and increasing weather system activity moves into the region as the jet stream strengthens and moves southward (see average color radiation below).

So enjoy the warmth of the next two days.  This may well be the last 70F+ highs you experience for many months.