Not All Daily Temperature Records Are the Same

Yesterday, the temperature at SeaTac Airport rose to 89F,  beating the all-time daily record for the date (86F)!

Today, even if the temperature is the same today, it won't break any records.

How could this be?

It turns out that not all records are equal.

Let me explain.

Below is a plot of observed temperatures (blue bars), average temperature range (brown band),  and record highs (red) and lows (blue) for June at Boeing Field in Seattle.

Look carefully at the record highs.   A large variation of record highs in June from 81F to 104F!  Generally around 90F.   

So why the variability?    

It turns out that to get the really high temperatures in western Washington, the atmosphere needs to organize itself in a very specific way, generally with a strong upper-level ridge and offshore-directed flow at low levels.

And on some days, by the luck of the draw, the atmosphere gets the right setup for maximal heat. After many years, the needed flow pattern occurs, and the temperature climbs to record levels.

Global warming plays very little role in these records---the key is getting the right atmospheric flow situation.

Would you like me to prove this to you?

Here is a plot of the highest maximum temperature each year between June 7 and June 21 since 1950 at Olympic Airport (a less urbanized location than SeaTac).   No apparent upward trend.

Turning back to SeaTac, below is a plot of the highest temperature on June 14th at that location (below).  

2025 was the warmest year on record for that date.  But note!  There is no trend in the record temperatures for that date over the entire period of record.

In fact, the highest temperatures on June 14th are trending down!  (brown line).  

So the global warming claims for the origin of such records should be taken with a large grain of salt.

Meteor Clouds

Some of the greatest treats of June are the relatively rare but stunningly beautiful noctilucent clouds that form very high in the Earth's atmosphere during this time of the year.

Thursday night, there was quite a show, as illustrated by the pictures below.

Picture courtesy of SkunkBay Weather (from central Puget Sound)

Eastern WA

Noctilucent clouds form high in the atmosphere, about 50 miles above the surface, when water vapor condenses on meteor dust, producing small ice crystals that make up the clouds.

Such clouds are only apparent from late May to early August within a relatively narrow band of latitudes (roughly 50 to 70 degrees)--leaving Washington State on the southern edge of the viewable domain.

Why such limitations, you ask?

First, the formation of such ice requires very, very cold temperatures and the upper atmosphere (called the mesosphere) is coldest during late spring and summer.

Second, the clouds are best illuminated by the sun located below the horizon, and summer provides the optimum sun angle.

Short Heatwave Followed by Normal Temperatures and Precipitation

It is now clear that our region will experience a short-period heatwave on Sunday and Monday, with the highs in Seattle reaching near 90F and eastern Washington climbing into the upper 90s.

This is after a relatively cool start to June and the expectation of normal temperatures the rest of the month.

A plot of the temperature at SeaTac, with observations (blue bars), and record highs (red) and lows (light blue) shown, indicates that we have generally been cooler than normal this month.  Record highs on any day are generally around 90F.

The crazy record high in 2021 is evident at the end of the month.  

To put this month in a better long-term perspective, I have plotted the average maximum temperatures at Seattle from 1-10 June for the past 50 years (a trend line is also plotted).

We have started this month, a bit below normal.  But you will notice a small upward trend (brown line) since the 1970s.   That could well be the influence of human-caused warming produced by increasing greenhouse gases.

Now turning to the forecasts, below is the latest National Weather Service forecast for Seattle. Friday and Saturday will be comfortable, but then temperatures increase, reaching 90F on Monday, before declining to normal next week.

Eastern WA will also warm, with the Tri-Cities climbing into the upper 90s before cooling into the mid-90s.   These are not exceptional temperatures in the central Columbia Basin.

 After this warming period, substation precipitation is predicted to return to the region, as shown by the total accumulation through thourgh June 25th (below).    Particularly heavy in British Columbia, which is very good for the Columbia River.  Very favorable for our power generation and irrigation needs.

Recent substantial rain has contributed to Yakima River storage, which is almost exactly at normal levels.   Very good for irrigation in the Yakima Valley this summer.

Meteorological Roller Coaster

June is an interesting weather month in the Northwest.

The sun is very strong, so with the right conditions, temperatures can zoom up to extremes, such as the stunning heatwave of late June 2021 (108°F in Seattle).  On the other hand, with moist onshore flow, our temperatures struggle to rise into the 60s.  The Pacific Ocean off our coast is only around 50°F.

During the next week or so, we will experience a prime case of a meteorological roller coaster.

Consider the latest forecast for Seattle from the European Center model (below).

A high today (Monday) in the upper 50s, with a slow climb into the 70s by Saturday.   Then a sprint to around 90 degrees, followed by a nearly 20F decline next Wednesday.  This is followed by a rise into the upper 80s, with a huge cooling in the subsequent days.

My head is spinning!

The potential to get warm in June is illustrated in the climatological highs (red) and lows (light blue) below for Seattle, with the temperatures this year shown by the dark blue bars (brown indicates the average range).

Once we get past mid-May, high temperature records reach the 90s.  Once in June, low temperatures remain above 40F.

But to get the heat, as will occur in a week, requires offshore-directed flow that pushes the cool, marine influence offshore.  Such easterly (from the east) winds result in downslope flow on the western sides of the Cascades.

Downslope flow warms rapidly by compression as air traverses from low pressure aloft to high pressure near the surface.  

Today (Monday), a very wet weather system is moving in (see satellite image), with clouds, precipitation, and very cool onshore flow.

But in a week, high pressure will build inland, producing offshore-directed winds and profound warming.  

Consider the forecast for Sunday morning for sea level pressure (solid lines), low-level winds (the wind barbs), and low-level temperature (shading), shown below.

A transient high has moved east of us, producing winds from the east to the west. The air warms as it sinks on the western side of the Cascades (pink colors).  Warm air is less dense than cold air, which results in lower pressure over western Oregon and Washington (called a trough in the weather business). 

This situation won't last long, because the high pressure to the east will move away.   As it does so and the winds from the east weaken, the winds from off the ocean will surge in, producing rapid cooling--something called an onshore or marine surge.  

To illustrate, the same map for Wednesday morning is shown below. The reds on the west are replaced by cool greens.  You may need a sweater again.

As discussed in a previous blog, the "locked up" pattern of the past winter has been replaced by one in which pressure systems progressively move through the region.  Thus, we will experience a range of weather conditions, from warm and dry to cold and wet, and meteorologists will have less boredom to contend with.

Northwest Mountain Snow in June: A Cold/Wet Period for the Northwest

The images from the Mount Rainier Lodge area during the last day were winterlike, with several inches of snow on the ground

The Crystal Mountain ski area was similarly snow-covered.

And Whister Peak appeared more like March than June 

Thunderstorms, with small hail, hit both sides of the Cascades, with substantial precipitation totals yesterday (Saturday); many mountain locations received over an inch of liquid water.

This situation has brought much colder than normal temperatures to the region, with many locations 10-20 F below climatology ( see below).   Many higher terrain locations did not get out of the 30s!

But even colder and wetter weather is in the forecast, with major positive implications for water resources this summer.

The forecast temperature anomaly (difference from normal) for the region for Tuesday to Wednesday morning (below) is for 5-15F below-normal temperatures, with the coldest temperatures over the Cascades and eastern Washington and Oregon.

Wet conditions will dominate from late Monday into Tuesday morning, with some locations in the Cascades receiving 1-3 inches.    Very favorable for water resources this time of the year: moistening the soil, filling reservoirs and rivers, and reducing water demand.

The origin of this cold/wet period is anomalous low pressure (roughing aloft in meteorological parlance), as shown by the upper-level  (500hPa, roughly 18,000 ft) forecast map for Monday at 5 PM.  Blue indicates the low/pressure/troughing

Temperatures should recover a bit by the end of the week (see forecast through Friday for Seattle, shown below), but we will have to endure a cool/wet period first.

Wet, Cool Winter-Like Weather in June

During the next week or so, the weather will be more reminiscent of February than June, with lots of rain and MUCH colder than normal temperatures.  

Reservoirs, already above normal, will be topped off, streamflows will be substantially enhanced, and soils moistened.

Let's begin by looking at the predicted precipitation totals (by the European Center Model).

Through Friday, some regional light rain (see below)

The totals through Tuesday morning are getting serious, with windward (western) slopes and higher terran of the region wetted by as much as 2-3 inches.

Values of cumulative precipitation over the next 15 days are quite extraordinary, with substantial rain even falling over eastern Washington.

Now I will show you something hard to believe.  

A very, very strong atmospheric river will be aimed right at us on Sunday evening (a measure of the amount of water moved by the atmospheric river is shown). 

Just stunning.

Not only will it be wet, but much colder than normal, which reduces evaporation considerably and encourages water to percolate into the soil.  

Below is the forecast difference of temperature from normal for the next five days.  

Brrr! The whole region is 3-6F colder than normal,

Next five days?   Double Brrr!   The entire region remains cold!

The NOAA Climate Prediction Center is going for wetter than normal for their 5-10 day forecast:

And the NOAA Northwest River Forecast Center predicts that local rivers will rise substantially.  For example, consider the Yakima River, which is of prime interest these days.  Big jump upwards.

Having an extended cool, wet period at this time of the year is extremely favorable for both water supply and agriculture.   

Hopefully, the "extreme drought" hype will fade now.

Dramatic Mirage Over Puget Sound and a Super Sea Breeze

Today was the warmest day of the year so far, with some western Washington locations reaching the mid-80s, bringing some strange and remarkable weather features to our area.

First, there were some dramatic mirages for locations near Puget Sound.  Sandy beaches became sand cliffs, mountains were thrust high with strange valleys, and houses were displaced into the sky (see sample below off of Whidbey Island)

Picture courtesy of Greg Johnson 

 Want to be really impressed?  Play the video below, provided by Greg Johnson of Skunk Bay Weather.

So what is going on?  

Superior mirages produced by the intense inversion (temperature warming with height) in the lowest few hundred feet of the atmosphere.  

Why such a strong inversion?  Because we had very warm air above our cold (about 50F) water.

To illustrate, below is the temperature variation with height (red line shows temperature) at Forks, near the NW Washington Coast.  Temperature is in C (x-axis), and height is in pressure ( hPa, 850 is about 5000 ft).

An intense 15 °C low-level inversion (again, temperature warming with height) near the surface.

Such inversions act as a lens that bends light, making objects look higher than they really are.  Superior in this case means higher.

But not only did we have crazy optical effects, but we had a super sea breeze on the coasts.

So strong that its leading edge was apparent in the weather radar around 1 PM  today (dark blue line):

At Hoquium, near the Washington Coast, the sea breeze front produced a rapid wind shift from easterly to northwesterly around 1 PM, accompanied by a substantial acceleration of the wind speed.

Temperature peaked around 80°F before the sea breeze hit, and then dropped into the 60s by late afternoon.

Our short heatwave is over, and western Washington should remain below 70F for the next week.  Plus, lots of rain over the weekend.

The Real Story of the D-Day Weather Forecast

The anniversary of D-Day is coming this week, and a movie has just been released about the D-Day weather forecast (called Pressure).

The movie follows the plot of the play of the same name, describing how a weather forecaster (James Stagg) pushed to delay the landing due to a storm, was opposed by an egotistical American meteorologist, and that the German forecasters were wrong, leaving the German defenders unprepared.   

New information from Allied and German archives and modern reconstructions of the weather during the landing period reveal that some of the "Pressure" story is not correct.

June 6, 1944

The landing in Normandy had several key environmental requirements.   

A full moon was needed to provide sufficient illumination for gliders and parachute troops the prior evening. No low cloud base that would prevent close air support and accurate naval bombardment along the coast.    Low tide conditions, so dangerous beach obstacles could be avoided.   Furthermore, winds had to be light so that waves and swell would be minimal.

June 4-7th had the requisite lunar and tide conditions, with the next opportunity not until later in the month.  And it was a matter of time before the Germans figured out where the real invasion would take place.  There was strong pressure to move sooner rather than later.

Three forecast groups were represented in the overall meteorological team: two British (UK Meteorological Office and British Navy) and one American (headed by Dr. Irving Crick).  The meteorological leader was the Royal Air Force's James Stagg.    

The British meteorologists made use of traditional forecasting approaches that relied on the Norwegian Cyclone Model, with a typical evolution of cyclones and fronts (see below), while the Americans used a controversial "analog" approach, where one searched for similar weather situations in the past.

Weather prediction was a primitive, subjective affair at that time.  There were no numerical weather prediction models, little understanding of jet streams and upper-level weather features, and an acute lack of observations, particularly over the ocean.

The situation on June 4, 1944, was problematic (see the Allies' sea level pressure analysis below).  A fairly strong low center was approaching northern Scotland.  The lines are isobars, lines of constant pressure, and where they are close together, the winds would be too strong.  Plus, a cold front was approaching (the line with the triangles on it).   

Not good for invasion:  winds would be too strong on the beaches, with lots of wave action and high water level (could not see the obstacles).

The weather map on June 5th indicated that the low had strengthened but had moved to the northeast (see below).  An area of high pressure centered west of Spain was starting to extend northward into the region.  Winds would still be significant, but the situation might be improving.

The forecast team under Stagg predicted the low would continue northward, producing conditions just good enough for D-Day on June 6th.   The actual weather map for June 6th (below) suggests that Stagg and associates made the right forecast for the wrong reason. 

As noted in an excellent recent paper by Anders Persson, the storm did NOT move to the northeast as predicted but weakened rapidly and slid southeastward.  Problematically, pressure differences over the channel were large enough to create significant wave action, which caused extensive sea sickness, high water levels on the beaches, and lost equipment and deaths.  

The disliked American forecaster  (Irving Krick) has been right about a pattern change that would push the low south rather than to the north, as predicted by Stagg and friends.

The situation was marginal, but just good enough for the landings in Normandy.

It has been thought that the Germans had poor weather maps over the eastern Atlantic because they had few weather assets over the Atlantic (and none over North America).  

But as noted in the article by Anders Persson, it appears the Germans had decoded Allied weather communications and possessed relatively good weather maps.  They assumed that the marginal conditions on June 6th were not good enough for an invasion, resulting in a lack of readiness and the absence of General Erwin Rommel to visit his wife on her birthday.

But the story does not end there.   

During the past decade, the meteorology of the period has been simulated using modern weather models and data assimilation tools, giving us a far more accurate description of what occurred during the D-Day period.

Below is an animation of the hourly precipitation (color shading) and sea-level pressure on June 6, 1944, made by the European Center (the ERA5 analysis).  You can see the low northeast of England weakening and moving southward.    Not what Stagg expected.

Although marginal, conditions were just good enough for a successful landing on Normandy, although the high winds were very problematic.