July 10, 2024

The Cooling Has Begun

 The differences in temperature between noon today (Wednesday) and yesterday are quite large west of the Cascade crest (see plot below).  Some locations are 15-20F cooler, particularly across southwest Washington and NW Oregon.

The Columbia Basin temperatures were relatively unchanged.

With cooler air moving in across the coastal region, low-level air pressure is increasing there, producing an enhanced difference in pressure across the Cascades.

Such increased pressure differences increase westerly winds (winds from the west), and we can see the wind strengthening over the eastern slopes of the Cascades.  For example, the wind at Ellensburg is now gusting above 35 mph (see plot below).


Such increased winds result in increased wind energy generation (see green line below), which is good...we need it.


The next few days should bring steadily declining temperatures over western Washington.

Let me show you the state-of-the-art UW ensemble of many high-resolution forecasts for Seattle temperatures.  High around 85F today and 80F tomorrow.  Temperatures at night decline to the upper 50s.  Decent sleep beckons. 


The National Weather Service NBM forecast is similar and very boring.  No heat waves. No cold waves.  Just perfect weather rising into the lower 80s.



In contrast, the Tri-Cities will remain around 100F for the same period  (see below).


No rain is predicted on either side of the Cascades during the next week.  

Enjoy the weather.



July 08, 2024

The Current Northwest Heatwave: Facts Versus Hype

 We are now in the middle of a heatwave period in which some locations have broken daily temperature records (records for a specific day)

Let me describe what is happening and why.

Below are the high temperatures yesterday (Sunday, July 7).   70s along the coast and over the marine areas of NW Washington.  Lower 90s in Puget Sound, around 100F in Portland, and low 100s over the Columbia Basin.


Why so warm?   

We start with being near the time of maximum sun strength and length of day.   Temperatures can warm until 5-6 PM this time of the year.

But the real secret is the position of high pressure aloft, positioned today and yesterday in the "sweet spot" for Northwest warmth--over southwestern BC.  The map below shows the upper level (500 hPa) map today, with the shading showing the difference of the values from normal (orange and red are above normal).  Perfect for local warnth.


And yes, there is global warming.  You can give credit for about 2F of the heat to increasing greenhouse gases.   For example, a location that reached 93F yesterday, would have been 91F.   

We still would have had a heatwave without global warming.

So what about the future? 

The Seattle Times is up to its old tricks and stating that a "100 Degree Heat Wave" looms for Puget Sound (see front page clip today) and "among the warmest nights in history."   Scary stuff.

And not true.

Let's look at the surface air temperature predictions from the very high-resolution UW forecast model near the time of max temperatures (5 PM)

At 5 PM, most of Puget Sound country is in the upper 80s and lower 90s, but warmer around Portland, and MUCH warmer (over 100F)  at the lower elevation of the Columbia Basin.

 
Tomorrow is much of the same story west of the Cascade crest, except a few degrees warmer south and southeast of Puget Sound.  

Sorry, Seattle Times....no century temperatures predicted near Puget Sound.    But much warmer around the Columbia Basin...over 104F in many places.


But what about Wednesday?  Much cooler in the west, and even eastern Washington starts pulling back. 


Why cooling?  Because the upper level ridge weakens and moves eastward and an upper trough of low pressure moves in (see upper level map for Wednesday).  Marine air starts to push into western WA.


But there is a danger in this change.

As cool air and high pressure build into western Washington, it will produce strong winds over the eastern slopes of the Cascades (see wind forecast for late Wednesday).  Reds, grays, and greens indicate stronger winds.


Winds that can rev up and wildfires.  

Finally, what about the Seattle Times claims about us experiencing one of the warmest nights in history?

Just wrong.

Even at crazy warm SeaTac airport the low temperature last night was not even close  to being a record (see below).  The plot shows the highest minimum temperature each year and the red line is last night at SeaTac.  Many years had warmer minima.

And using a far better station for climatological analysis (Olympia), last night's minimum was nothing unusual.  Most years have had warmer minima.


Stay cool....There is no major heatwave predicted for the next week.






July 06, 2024

Unbelievable Change in Temperature in a Very Short Distance

Can you imagine having the temperature change from a chilly 59F to a torrid 101F in only 3 miles?    Or a similar change ascending a modest mountain, with temperature INCREASING with height.

All this happened today in the Bay Area.  Perhaps this should not surprise us considering the craziness of San Francisco!

Consider the high temperatures today around the Bay Area.  59 F on the Pacific side of San Francisco, but 101F at the top of Mount Tamalpais, at around 2500F.   Even higher (105F) at a nearby mountain site.  About 40F change from Stimson Beach on the Pacific to the top of Tamalpais.....3 miles away.

 

Stunning contrasts.

This situation was characterized by the very cold water of the Pacific and an associated shallow cold air layer near the surface with an extraordinary inversion capping the cold air.

Below is an analysis of the sea surface temperature of California. (sorry, it is in centigrade),  Very cold water is found along the coastal zone of California, the result of upwelling cold water from below.

How cold?  About 9C or about 48F.  Wow...very cold.  This cold water chills the air right above.

We can check out the vertical temperature structure in the area using the ballon-launched radiosonde released at Oakland, CA this morning at 5 AM (see below).  Height is in pressure (850 is about 5000 ft, and the temperatures are in °C).  The right line is temperature, and the left line is dewpoint.

Mama Mia.  Was there an inversion!   A shallow, cool, saturated layer was apparent in the lowest few hundred meters, with a huge inversion overhead in which temperature increased from 14C to 35C (57 to 95F) in about 1500 ft.


What about our area?

Some impressive coastal contrasts exist today, but not in the same league.  Our coastal water is not as cold and the contrasts stretched over more distance.   To illustrate, here are the high temperatures today on the central WA coast.  60s on the coast and about 101F in the inland low terrain.  Still impressive.



Acknowledgment:  This amazing situation was brought to my attention by Dr. Peter Benda.



July 05, 2024

July 4th Smoke, Wildfires, and the White Sky

When you looked at this morning did you notice the hazy whiteness in the sky?   July 4th fireworks are too blame.    And such fireworks have started wildfires, including a major burn near Wenatchee.

Let's start by look at the Seattle Panocam at 6:30 AM this and yesterday mornings (below).  I bet you can see the difference.  At my home, the sky looked white near the horizon.  Why white?  More later.

Today

Yesterday, July 4.

Fireworks smoke has caused significant air quality degradation over much of the region.

The western map at 830 AM (courtesy of the Puget Sound Clean Air Agency), show poor air quality (red and purple colors) over extensive areas downwind of population ceners.


And the US EPA's AirNow graphic also show poor air quality near Wenatchee (see below)


Why Wenatchee?  Because someone ignited a major grass fire west of the town with fireworks (see map below).  That individual has been arrested.


 There is another grass fire, supposedly started by powerlines, southeast of Chelan.    The visible satellite image at 6:30 AM shows the smoke from these fires, plus the Pioneer Fire up Lake Chelan.



Plots of air quality (actually small particle concentrations) at Seattle and Marysville (both shown below) illustrate the rapid increase in smoke last night.  The Marysville numbers were crazy high (about 130).


Seattle

Marysville

Finally, why do these particles turn the sky white?

It turns out this is due to something call Mie Scattering.    When light from the sun interacts with smoke particles is it scattered by the particles in many different directions (see below)

Image courtesy of Virtual Labs

Light from the sun includes all wavelengths of visible light (from red to blue/violet).   Light appears white when all wavelengths are represented and if you were above the atmosphere the sun looks pretty white.


Large smoke particles from fireworks scatter all wavelengths of visible light similarly, thus producing a white-looking sky.  This is what is meant by Mie Scattering.  In contrast, small particles in a clean atmosphere (such as the typical gases) scatter shorter wavelengths (like blue) more (called Rayleigh Scattering), which gives the sky a blue cast.    

Heavily polluted cities in China have a lot of big particles, so their skies almost always look white.  Perhaps it is ironic that our fireworks come from China.  They export their white skies to us during our day of celebration of independence.  






July 02, 2024

The Two Most Turbulent Airports in the U.S.

Many folks are flying this summer and most are not fans of in-air turbulence.

So which airports are most prone to turbulence and why?    

And if you are flying to one of these destinations, how can you minimize the risk of a bumpy flight?

All will be revealed in this blog.

Recently, the aircraft turbulence website, Turbli, published its analysis of the most turbulent airports in North America (see results below).  The top two are Portland and Denver.


I can certainly confirm the results for Denver, to which I fly all the time (the National Center of Atmospheric Research, NCAR, is in nearby Boulder).

So why are landings and take-offs so turbulent for these locations?   

It is all about geography and nearby terrain barriers.

Portland

As shown in the map below, Portland Airport (PDX) is essentially due west of the Columbia River Gorge.


During winter, cold air and high-pressure build to the east of the Cascades, while low centers approach from the west.   The result is a strong pressure difference across the Cascades that produces strong low-level easterly winds in the Gorge that reach the airport (see model simulation below).


While the winds are strong and from the east at low levels, the winds above are generally westerly (from the west).  This produces a strong vertical wind shear (winds changing rapidly with height.

Strong wind shear is a principal driver of turbulent motions.  Summer conditions are less conducive to Portland airport turbulence.

Denver

Denver Airport (KDEN) is northwest of the city and just east of the Front Range of the Rockies (see map).

The Rockies are turbulence generators throughout the year.

During summer, and particularly from June through early September, thunderstorms develop over the Rockies during the late morning and early afternoon and then drift towards the airport.   Thunderstorms produce lots of turbulence.  

Check out his satellite picture for midday on June 23rd...you can see the cumulus clouds bubbling up on the Front Range.   Fly in from Seattle and you will fly through these clouds and will bump around considerably.


If you want to avoid summer turbulence at Denver, FLY IN or OUT EARLY before the thunderstorms rev up.  My rule of thumb:  don't fly in or out of the DIA after 11 AM during the summer.

There are few such thunderstorms during the winter, but there still is plenty of turbulence, this time from strong mountain waves downstream (east) of the Rockies (see schematic below).   Such mountain wave turbulence is encouraged by strong westerly winds approaching the crest of the Rockies for the west, a very frequent situation during the winter!


Such mountain wave turbulence can be extreme.

Happy flying!


June 30, 2024

Summer Starts on Tuesday: My New Podcast is Out

This year is pretty typical:   a relatively cool and moist June, followed by a transition to consistent warm/dry days in early July.

Weather perfection is ahead and my blog describes the shift from June Gloom to Summer Sun.

Check out the latest NWS National Blend of Models Forecast for Seattle (see below).  After Tuesday, a steady climb into the lower 80s, with no rain and plenty of sun


So why the transition to perfection?

During the past month, a series of upper-level troughs of low pressure have moved through, bringing periodic showers and cooler temperatures.   The upper-level map at around 18,000 ft (500 hPa) for today at 2 PM is shown below.  Trough over the Northwest and a ridge offshore.   Not a warm pattern!


But by Thursday, the trough has moved inland and the ridge is developing offshore.  Not too strong (which would bring a heatwave) but just right.


And four days later the ridge is still there, extending northwest towards Alaska.

So you should have perfect weather for enjoying the fireworks,  having a barbecue, or going on that long-planned hike.  A good time for meteorologists to go on vacation.

In my podcast, I talk about fireworks...please be careful.   We have enjoyed fewer wildfires than normal this year...let's keep it that way.

You can listen to the podcast below or through your favorite podcast server.


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June 27, 2024

Huge June Precipitation Contrasts Across the Region

If you think rainfall at your location is representative of the region....think again.

This June there were huge precipitation contrasts.

Consider the accumulated rainfall from June 1 to yesterday (June 26 is shown below).

Wow.   The windward (western) side of the Olympics received 5-7 inches so far in June.  In contrast,  only 1-1.5 inches fell over Puget Sound and under a half-inch dampened Sequim, northwest of the Olympics.  

Over TEN INCHES at some locations on the western slopes of the Cascades, declining to under a half inch along the eastern slopes of the Cascade and into the Columbia Basin.



A closer look at the contrasts from Seattle to the Cascades is shown below.  From 0.79 inches over western Seattle to 11.30 inches in the terrain.   



The bounty of western Cascade rain has not only dampened some hikes but have led to healthy river levels.  Below is the latest USGS river level plots.  Most western Washington rivers are near normal (light green) and some above normal (dark blue).   In contrast, some rivers on the eastern Cascade slopes are below normal.



The western side of Washington and particularly the western slopes have been wetter than normal while the eastern slopes of the Cascades have been relatively dry.   Why?

This month the winds approaching the region have been stronger than normal.  Stronger-than-normal winds from the west.  Such a wind field enhances upslope flow and thus precipitation on the western sides of mountain.

In contrast, enhanced winds from the west produce stronger descent and rain shadowing on the eastern side of barriers---producing a strong rainshadow.  
What set up the strong westerly flow this this month?   

Below are the heights at 850 hPa, which you can think of as pressure around 5000 ft.  Lower values over the Gulf of Alaska and higher values to the south.  This pressure pattern produces west-southwesterly winds approaching our coast (white arrow).

How was the situation this month different from normal?  That is shown below (the anomaly of 850 hPa height--think pressure at 5000 ft) .    This month we have had a stronger than normal low over the Gulf of Alaska, which helped enhance the southwesterly flow and brings more moisture into the region.

The Cooling Has Begun

 The differences in temperature between noon today (Wednesday) and yesterday are quite large west of the Cascade crest (see plot below).  So...