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.

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.