3D Northwest Heat

 We are now in a short warm spell with temperatures getting into the mid 80s to lower 90s in western Washington.  Cooler weather (and some rain) will arrive next week.

 But for me, one of the most fascinating aspects of our warmth is how three-dimensional it is.  How spatially varying the heat can be.

Let me show you, by starting with yesterday's highs (below). Mid-80s around Seattle, 70s and low 80s over Northwest Washington, around 100F in the Willamette Valley, and upper 90s in the Columbia Basin.   An interesting feature is the near 100°F in the higher terrain between Olympia and the coast,.

In western Washington, the influence of the cool Pacific and inland waters results in cold air near the surface, but warmer temperatures right above.  This is particularly true when (like yesterday) there is easterly  (from the east) flow aloft moving warmer air from eastern Washington towards the west.

Yesterday (Friday) morning, this situation was so profound that there was an inversion (temperature increasing with height) above Seattle, something illustrated by the temperatures above SeaTac Airport at 8 AM (below).  Temperatures in the mid-60s near the surface, but 70s above 2200 ft.  

A profound inversion from 1000 to 2500 ft (more than 10 degrees).  I bet morning hikers noticed this warming with height!

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This morning at 7 AM, the inversion was even stronger  (see below), going from 67°F to 79°F above 1500 ft.

The inversion weakened during the day as solar heating warmed the surface.

A temperature inversion can act as an atmospheric lens for weather radar beams, causing  the radar beam to bend downward to the surface, which acts as a target.

This inversion bending of radar explains the huge number of false radar echoes off our coast right now (see below).  The radar beam hits the ocean surface and then is reflected back. 

Looks like a lot of rain out there...in reality there is nothing.

When we have inversion conditions, maps of temperature can get jarring, such as this morning at 7 AM in the Cascade foothills near North Bend.  Around 70°F on ridgetops but lower 50s and 40s in valleys.

According to the latest National Weather Service forecast, the warmth will continue over the weekend, with cooling by mid-week.  Possible rain next weekend.

The Patterns of Warmth

I have always been fascinated by the complex temperature patterns of the region, controlled by our substantial terrain and land-water contrasts.

The warming period over the next few days presents a great opportunity to view such temperature structures, so let's take advantage of this period by viewing the ultra-high-resolution forecasts run at the University of Washington.

Starting with the surface (2 meters above the ground) air temperatures for 5 PM today, you find the warmest temperatures in eastern Washington (away from the cooling of the Pacific) and in the lowest elevation of the Columbia Basin and river valleys.

Far cooler at higher elevations in the Cascades and Olympics and near the waters of the Pacific and Strait.   Northwest Washington (e.g., San Juans and Bellingham) is cooler than the South Sound,

The Willamette Valley (including Portland) is the warmest area west of the Cascades due to its isolation from the cool Pacific.  Why? The coastal mountains are an effective barrier, and the Willamette Valley doesn't have sea level conduits to the Pacific like the Puget Sound region.

On Thursday, high pressure will build overhead and temperatures will warm, particularly over the Willamette Valley and southwest Washington, with a cool zone remaining on the coast.  Portland will be toasty, but Seattle will only peak out around 80°F.

 

Note that eastern Washington is almost unchanged.

Friday will be different:  MUCH warmer, as a ridge of high pressure aloft builds over the  West Coast.  

Upper-Level (500 hPa pressure, ~18000 ft)Friday afternoon)

Here are the predicted temperatures.... wow.  Portland is warmer (upper 90s) than the Columbia Basin, and Puget Sound (away from the water) is in the 80s. Still some relief on the coast and Northwest Washington.

Why is western Washington warming?  

Because easterly, offshore-directed flow reduces the marine influence and provides some compressional heating on the western side of the Cascades as air from eastern Washington descends the slopes.

The nice thing about living here is that it is almost always possible to escape the heat: you can go up in elevation, head to the water, or check out northwest Washington.  A Washington State Ferry ride is usually a good, cool bet, with the warmest period often producing interesting mirages.

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Record Water Vapor Values Hit the Northwest

On Friday, substantial rain hit the Northwest, with some stations receiving their typical rainfall for all of August in one day.   No annual daily precipitation records were broken, but several stations exceeded records for that date.

The forecast model predictions (below) verified very well, with 3-6 inches in favored locations on the western sides of local terrain.

But there was something really unusual about the situation on Friday.

The moisture content of the air.  

Something called the Total Precipitable Water Content (TPWC),  the amount of liquid water that would result if ALL the water vapor in a vertical column of air were precipitated out.

At Salem, Oregon, the amount reached 1.82 inches, the highest value EVER observed at that site (see below).  In the plot below, the red line shows previous daily record values.  

Values are high in summer since warm air can hold more water vapor, among other reasons.  

As shown by the short-term forecast (valid 5 PM Friday) of the Total Precipitable Water Content, the plume of high values extends all the way back into the eastern Pacific.  More on that later.

Dew point is a measure of the water vapor content at one elevation (generally at 2-m above the surface). 

Here in Seattle, we experienced the highest dew point (65°F) since August 2022 (see plot below).  It was very "sticky" on Friday.

The heavy precipitation from this moisture plume (which some folks call an atmospheric river) resulted in amazingly rapid rises of actual rivers in the localized zones of heavy upslope precipitation (such as the NW Olympic Peninsula and the western slopes of the central and northern Cascades).

Consider the South Fork of the Sultan River in the foothills of the central Cascades (below).  The black line shows the river discharge, brown shows the record lows, and blue shows the record highs.  

Wow.  A stunning rise from a near record low to exceeding the record high for that date.

High river levels closed several roads, including the entry to the Hoh River Valley.

Although the water vapor levels of this atmospheric river were record high, the atmospheric river was relatively run-of-the-mill.

How can this be?  

The key measure of atmospheric river strength is how much water vapor is moving in over a unit of time.   That depends on BOTH the water vapor content AND the wind speed.

The water vapor content of this event was very large, but the wind speed was modest.  Think of a river with a very high level, but a weak current.

Finally, why was this moisture plume/atmospheric river so moist?

We start with the optimal time of the year (late summer), when the atmosphere is most moist.   I checked it out:  the vast majority of the intense moisture plumes in our region occur in July to September.

Second, the North Pacific is now unusually warm (see below), mainly due to an anomalous atmospheric circulation during the last year.

Red and orange colors indicate above-normal water temperatures.

Third, the large-scale atmospheric circulation took unusually high values of water vapor over China and moved it across the Pacific. (orange and reds are high values)

Atmospheric Moisture On Wedneday

And this moisture was concentrated by a strong low in the Gulf of Alaska

And finally, what about global warming?  Yes, a warming planet results in more evaporation from the oceans and higher atmospheric water vapor content.  

So the roughly 2°F global warming would have helped, but probably was not the dominant cause. 

How can I say this?  I plotted the years of the top 25 events at Salem, Oregon.  If global warming were dominant, there would be a clear upward trend.

A weak increase over time, but clearly not the dominant story.

What Season is This?

The visible satellite image this morning was stunning, reminiscent of an image from mid-winter (below).  The star shows the location of Seattle. 

 You can see the swirl of clouds around a deep low-pressure center west of British Columbia, a strong front offshore, and unstable air with convective clouds south and southeast of the low.

Impressive.

It is times like this that we should be glad that we have a coastal Doppler radar (thank you, Senator Cantwell), which shows the approaching frontal rain band offshore (see below).

This rain will come in later today, bringing another period of moderate precipitation.

Below is the latest high-resolution UW WRF model forecast of accumulated precipitation through 5 AM Saturday morning.

Very, very wet in the mountains, with large areas getting more than 3 inches.

Rivers are going to surge rapidly, as illustrated by the predicted discharge on the Snoqualmie River near Carnation (below).  If you go to Snoqualmie Falls on Sunday, you won't be disappointed. 

Another interesting aspect of this event is the high humidity today.  Dew points are reaching the mid-60s, making it feel sticky ....reminiscent of the East Coast.   

Note:  the dew point is the temperature to which air needs to be cooled to reach 100% relative humidity.  The higher the dew point, the more moisture the air has.

At SeaTac, the dewpoint today is the highest of the year!  See plot below

 There are some amateur YouTube sites and some media claiming that this is a highly unusual, record rainstorm.

This is not true. 

Having a strong event like this in mid-August has occurred numerous times before.    Below is a list of the record one-day totals for mid-August (Aug 4-21) at Seattle.

Yesterday's total of .22 inches was 44th on the list.  Today, SeaTac may get a half inch, which is certainly not without precedent.

Extraordinary Dual Wildfire Smoke Plumes

In ancient Rome, gladiators would face the crowd and say, "We who are about to die salute you".

Today, we have the meteorological version of this.

Look at the visible satellite image this morning.  There are two west-to-east smoke plumes, hundreds of miles long.

One originates on the Olympic Peninsula (the Bear Gulch Fire) and the other on Vancouver Island (Port Alberni fire) 

Neither fire was that large.....they are NOT megafires (sorry Seattle Times and NY Times).  Each is around 5000 acres.  

But they are smokers, burning in areas that have been logged with lots of  flammable debris on the ground (see example near the Port Alberni fire)

Fortunately, the days of these fires are numbered.  

As mentioned in my last blog, heavy rain is coming to the coastal mountains.    

Below is the current forecast precipitation total through Saturday at 5 PM.  Three to five inches of rain on west-facing slopes.    Substantial rain over eastern Washington.

A less-than-average wildfire season so far is going to end that way.

Rapid Cooling, Heavy Rain, And Near Record River Levels

 Today may be the last day you will need air conditioning this summer in western Washington.

And fears of wildfires west of the Cascade crest should fade as well.

Heavy rain is coming to western Washington, accompanied by dramatically cooler temperatures.

When I plotted the predicted accumulated rainfall through Saturday morning from the UW model forecast, I could hardly believe my eyes (see below).  

Was the mid-August or September?

2-5 inches of rain on the western slopes of the mountains....wow.  Enough to radically reduce subsequent wildfire threats for much of the region.

Importantly, lots of rain will push into eastern Washington.

Several western Washington rivers will surge to near record levels (for this time of the year).   For example, the flow of the Snoqualmie River will jump dramatically, near the red markers showing the previous daily records.

The level of the Skohomish River, not far from the Bear Gulch fire, will surge upwards as well due to the heavy rain on the Olympics.

If this is not shocking enough, check out the predicted temperatures from the NOAA/NWS GFS model for Seattle.

Low 90s today, Low 70s tomorrow.   But the shocker is Friday.  HIGHS in the low 60s.  Stunning.

I have a lot riding on this cool forecast.  My 20-year-old AC unit failed today.  Surely it knew that it would not be needed again this season.  And my vegetable garden looks very sad from the warm, dry weather.  This will help.

Microscale Temperature Variations During the Summer

Have you ever experienced an unexpected breeze of cool air during an evening stroll after a warm day--like yesterday or today?

On such evenings, temperatures can remain warm on hilltops or broad, level areas, but on lower portions of slopes or downstream of terrain gaps, temperatures can be significantly cooler.   

Even during the day, it can be much cooler beneath vegetated slopes, particularly shaded ones. We are talking about 1-10°F cooler.  

 Downslope flow 101

Cooler air is denser (and heavier) than warmer air and tends to settle into lower elevations (see figure).  There is a fancy term for this: katabatic flow.

If you ever want to experience daytime slope cooling, on a warm day take a ride north from the University of Washington on the Burke Gilman Trail during the afternoon.  

Temperatures can be toasty south of the 45th Street viaduct, but north of there, the trail is adjacent to the east-facing vegetation slope (see picture) below, and temperatures are often 5-10F cooler.  I have measured this with a thermometer.

Moist, vegetated slopes are particularly powerful cooling machines because evaporation from moist surfaces is stunningly effective at cooling, particularly when the air is relatively dry.

It takes 540 calories of heat (from the sun) to evaporate one gram of water.  This is why evaporative coolers can be so effective.

Being in a shaded stream valley can be particularly cool.  There is such a location on the Burke Gilman Trail in north Seattle, just south of NE 55th Street (see map and picture below).    I call it "Chilly Valley" and it is often iced up in winter when every place else is clear--frequently 5-10°F cooler than areas to the north or south.

During warm nights, the higher elevation view homes are often much warmer than the low-rent locations to the south.  

For example, walking around with a thermometer in the neighborhood below,  temperatures were 4°F warmer at the top of the slope than at the bottom.  

It may seem nerdy to walk around with a thermometer, but it sure can be interesting. 😊

 

Birds Know That Summer is Ending Soon

 Here we are enjoying summer warmth, but other species know that ideal weather is ending soon.

How do I know this?

Birds have started to head south now in large numbers.

 One way I monitor bird migration is through weather radar, which picks up the movement of birds, with migration generally more evident at night.

For example, the radar this evening "lit up" with echoes after sunset....and this isn't rain.... It's birds (see below).

And by using the Doppler capabilities of the radars, we can determine the direction of flight.....to the south.   Here is a recent Doppler velocity image from the Camano Island radar:

Green indicates the target is approaching, red means moving away.  Thus, this Doppler radar image suggests movement to the south or southwest.

Then there is the BirdCast website, which heavily uses weather radar as a potent tool (below).  Lots of southward movement over the West.

Finally, the birds will have very nice flying weather for the next few days.   A significant ridge of high pressure has developed offshore (see map for 5 PM Sunday) that will bring warm, but not too warm, conditions over western Washington (mid-80s).

But this pattern won't last, and next weekend looks cooler with a chance of precipitation.

False Stories in the New York Times and the Seattle Times on Western Washington Megafires

Yesterday, the New York Times ran a story that was blatantly false, with the Seattle Times featuring it as well. 

The claim:  that Western Washington will experience more "megafires" due to human-caused global warming (climate change).  

Unfortunately, the writer of this story (a Washington State stringer for the NY Times) failed to examine the historical record or the best science, getting the essential facts wrong.

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How do I know the writer got it wrong?  

Because for the past two years, I have researched this very issue and just published a paper on this topic in the peer-reviewed literature (here).  I have read every paper and report on this issue.

So exactly that did the NY Times (and the Seattle Times) get wrong?

The article defines megafires as ones that involve hundreds of thousands of acres.  

How many such fires have occurred since 1900 in western Washington?

ONE.  The Yacolt Fire of 1902 (238,000 acres), just north of the Columbia River.

Has there been an increase in the number or size of large western Washington fires during the past 50 years, a period in which the Earth and our region have warmed?

The answer is no, which alone should make one doubt the NY Times claims.   

If global warming contributes to big fires, we should be seeing increases in the number of big western Washington fires due to such climate change.  We are not.   

The reason for this lack of correlation between warming and big local fires is clear.  

Big western Washington fires are very different animals from the small localized westside fires, such as the current Bear Gulch fire on the Olympic Peninsula (about 4000 acres now).

To have a "megaburn" burn in western Washington, one needs strong, sustained easterly (winds from the east.    No matter what the temperature, no matter what the prior rainfall, without strong easterly winds we do not get westside megafires.

It is very difficult to produce large wildfires in the very moist environment of western Washington forests.  Only strong easterly winds make it possible.

How do I know this?

Because in my research (again published), I looked at EVERY large western Washington and Oregon fire of the past 150 years, examining all available weather observations and simulating most of them with a modern high-resolution model (see sample below of near-surface winds for the 1902 Yacolt fire, colors indicate wind speed).

Every one of them was associated with strong easterly flow.

So what does this have to do with climate change and global warming?

It turns out that strong easterly winds are REDUCED  in our area under global warming/climate change.

You read that right.  The threat of the necessary strong easterly winds is LESSENED by climate change.

I can tell you why.  

Anthropogenic (human-caused) global warming is greater in the interior of continents than over the slower-to-warm oceans.  Virtually every climate simulation shows this...it is not controversial (see example below from regional climate runs made by my group)

Warm air is less dense than cold air, which results in preferential pressure declines inland than over the slower-to-warm coastal areas.

If pressure falls more inland (where it warms more), then winds tend to move from west to east (air tends to blow from a high-pressure area to a lower-pressure pressure).

Onshore flow like this is just the OPPOSITE of that needed for big western Washington wildfires.

To put it succinctly:  the NY Times and Seattle Times not only got the story wrong, they got it REVERSED.   Global warming will reduce the potential for western Washington mega-wildfires because the necessary easterly winds are weakened.

The writer of this story did not bother to examine the frequency of local megafires nor understand the meteorology that drives them.

Such sloppy and poorly researched "journalism" misinforms readers and leads to poor decision-making.    Very disappointing.