April 09, 2024

The Surprising Weather "Miracles" of Yesterday's Total Solar Eclipse

The solar eclipse had substantial impacts on local weather, some of which might surprise.

First, many reported a "miracle", with the clouds thinning just before the eclipse.

And the "miracle" was true, but there is a scientific explanation!  But first, let me show you what happened.

Just before the eclipse there were a lot of low clouds over the totality path in northeastern Texas (see blue oval area below)

But during and right after the eclipse, many of the clouds were gone (see below)


Divine intervention?  The influence of the prayers of the astronomically devoted?   

No, it was the result of the weakening solar radiation that caused the surface to cool.  Many of these clouds were shallow convection/cumulus, driven by solar heating (see figure below).  When the sun weakened, so did the clouds.


Not surprisingly, surface air temperatures cooled during the eclipse by as much as 5-10F at some locations.  To illustrate, here are the temperatures in Joplin, Missouri, where temperatures went from around 80F to 73F between 12:30 PM and 2 PM, before recovering during the next hour as the sun returned.


And then there was the wind.
  At many locations, there was a dramatic reduction in the wind speed during the eclipse.  Here are the temperatures and winds at another Missouri location (Folly Ridge).  Significant wind reduction during totality (from roughly 10 to 3 mph).




This can be explained by a reduction in vertical mixing in the lower atmosphere. 

Have you ever noticed that during the warm season, winds are greater during the afternoon and weaker at night?    During the day, solar heating at the surface causes vertical mixing, that brings strong winds aloft (not slowed down by the rough surface) down to the surface.  When the sun weakens, the mixing weakens, which reduces the flow of stronger winds to the surface.

Finally, there is another change I am not quite sure I can explain-- so maybe I better be careful about downplaying divine intervention.  

What am I talking about?  Changes in the weather radar imagery.

Consider the radar image from Dallas, Fort Worth, early in the morning (1406 UTC or 9 AM Dallas time).  Not many radar echoes.


Three and a half hours late (12:34 PM), there were lots of weak radar echoes.


But an hour later, near the height of the eclipse, there were few echoes...just like night.


And then an hour later when the sun returned, the echoes were back.


What is going on here?  What are these echoes?  Birds or bugs that like to fly during the day?  I will have to dig into this deeper.

In summary, by greatly changing the heating profile in the lower atmosphere, the eclipse had some profound, but temporary effects on many weather parameters.  


18 comments:

  1. We were near Brackettville TX for the event and that's exactly what happened. I had given up, but the skies cleared enough during totality to see the corona and one star. I'm going with answered prayers as the explanation.

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    1. of course, the exact same thing happened at Bertram County Park yesterday. awesome experience.

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  2. Contacts in Parma, OH {near Cleveland} experienced much the same conditions. Weather was nice and they ordered pizza and had salad and drinks. Several houses away, a similar gathering included fireworks and cheering. A good time - I suppose - repeated along the entire path of totality. Here in central WA, I didn't notice anything.
    [Thanks for the updates as this came and went. ]

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  3. What I love about the "no, it was..." explanation is that knowing how the natural laws that God put into place works does not explain away God answering prayers. I can see how a car engine works and what cause and effect of the environment are on its running, that doesn't explain how the engine was manufactured and made to be a running machine.

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    1. What? The engine was manufactured in a factory. The parts were made in a factory. It runs because ... combustion and gasoline. Sheesh. People and their "God" stuff.

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    2. Sorry, what? This is a science blog. The laws of the universe were not "put into place by God".

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    3. "The engine was manufactured in a factory." I graduated from UW with an engineering degree, so I can theoretically explain the manufacturing processes that go into building the engine. I can also speak to how the engine works. It is indisputed that the engine is man made. Built by a designer.

      Yet... No one can explain how life is made - what is life? - why is life?
      There are whole labs at UW devoted to biomimicry so that we can make engineering designs based on natural designs (yes I used the word designs). But curiously we still can't do it as well. Kinda dumb that man with all our intelligence can't do as well as accidents don't you think?

      It is far more likely that the "engine" happened by chance than the human brain.

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    4. The human brain evolved over millions of years through natural selection of characteristics which were most advantageous in surviving to adulthood and reproduction. Of course humans working for a few decades aren't going to do anything like that. Take a look at Prof Richard Dawkins' book The Blind Watchmaker for a detailed and enthralling discussion about this.

      Another problem with the god as designer is that it merely pushes back the problem of origin. How did the designer deity come about?

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    5. The basis of your argument is that it takes greater faith to believe that a deity could 'just be there' than it does to believe that we have evolved over time.

      I find it curious that the argument starts with natural selection - a process that requires tiny incremental steps over an extremely long period of time to create change. But. There are uncountable numbers of situations in nature that due to the complexity of the system, the change MUST happen all at once or the benefits are lost. Quite literally "the Chicken or the Egg" argument. *Side note just the term selection suggests there is someone or something doing the selecting.

      So I have to ask, how much faith does it take to believe that all-or-nothing complexity like life just happened by random chance?

      As for the origin of the Creator Deity - God. It is entirely logical - but certainly scary - that a created being would not comprehend a creator at all. The engine does not know the factory it is made in - or even why it was made, let alone who worked on it. So, this leads to the question: If there is a Creator - how does it affect my life?

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    6. We had the same break in Dripping Springs TX. My friends in San Antonio didn't have as clear of a break nor some of our friends in Austin. I'm grateful we got to enjoy clarity for most of it and all of of totality. Though with a couple mins of end of totality thick clouds rolled in.

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  4. I am suspicious of an interaction with urban pollution (mostly hydrocarbons), sunlight and condensation nuclei; their influence on clouds water droplets etc. Big topic in late 1970's and early 80's; smog in LA - I had a professor in WA that finally moved from Caltech because he got tired of hoping for a smoggy day so he could study it.

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  5. Super interesting post. Thank you, Cliff.

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  6. Hmmmm. And I thought a cooling air mass caused condensation into clouds

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    1. The surface cooled - not the air. Reread the story.

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  7. I think the reduction in weather radar reflectivity during the eclipse is in part due to reduction of Bragg scattering. The reduction in solar heating reduces the amount of turbulence at many scales including that of the weather radar wavelength (likely 10 cm).

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  8. Oh Cliff! You have opened up the Gates of Hell as far as mixing Religion and Science are concerned. If there was truly some divine intervention, the gods people believe in would have changed the path to include Washington State and avoid Texas entirely!

    A few friends went to view it from San Antonio. They ended up driving frantically for 3 hours on rural roads, sometimes at dangerous speeds (80+) looking for a hole in the clouds. They found one and saw the eclipse from 5 minutes before to 5 minutes after. My friend Jim is truly an eclipse chaser.

    Funny thing - we saw the 1979 eclipse from the very same hillock SE of The Dalles. We met in 1986 and just discovered that we shared this experience a few years back.

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  9. Wow - SO COOL! I just love how you explain these little subtleties. OF COURSE solar radiation (and the lack thereof) would influence wind and clouds - we've always known this but to see it in such a profound way with the abrupt "on/off" switch compared to the normal more gradual changes we see with sun rise and set - amazing!

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  10. We were in southwest Arkansas, and what started as a cloudy morning gave way to totally clear skies for eclipse viewing, which was spectacular. Even more spectacular, perhaps, were the thunderstorms that rolled in that evening, including a severe one that later spawned a tornado a county north of us. A great trip!

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