March 28, 2024

First Look at the Weather for the April 8 Solar Eclipse

 I have gotten a lot of inquiries about the weather on April 8, the day of the total solar eclipse of the sun over the eastern half of the U.S.

Our operational forecast models reach that far in time and have for a few days.  But considering the uncertainty at such a long projection, I have refrained from commenting until now.

The model solutions are starting to settle down and I have increasing confidence that I can provide useful information.  So let me do the first of several updates on the weather associated with the event.

The area of totality will extend from Texas to Ohio to northern Maine (see below).


Totality will occur at roughly 1800 UTC (11 AM PDT) for most of the path (earlier to the southwest, later to the northeast).   Here in Seattle, only about 20% of the sun will be covered (see below).  You would hardly notice this, even if the skies were clear.


The Forecast Situation

Below is the forecast 700-300 hPa (10,000-30,000 ft) relative humidity, a good measure of cloud cover, at 1800 UTC 8 April based on the U.S. GFS model.

Portions of southwest Texas might have a good view, but I worry about viewing conditions over much of the Midwest.  Some openings in Ohio and northern Maine.


But at this projection (270 hours), there is still substantial uncertainty.   Only when we get within roughly 5 days (120 hr) will confidence be relatively high in the forecast.

To illustrate the uncertainty, let me show you are series of forecasts for the above humidity field for four different forecast projections, but verifying at the same time (1800 UTC 8 April).  Specifically, you are viewing an animation of 288, 282, 276, and 270-hour forecasts of sea level pressure (solid lines) and the moisture field.  

All have some kind of low-pressure system and a plume of clouds in the middle part of the country and it appears the solutions are converging.  But there are significant changes between the forecasts.  

For Seattle, the variations are quite large.


An animation of the precipitation forecasts valid for the same eclipse time is shown below.   Enough precipitation to get a Midwest eclipse watcher nervous. And not promising for western Washington.


Another approach for such a long-term forecast is to look at the forecasts of ensembles of many forecasts.  

Below is the North American Ensemble Forecast System (NAEFS) prediction of clouds over Dallas/Fort Worth Texas over time.  I put a red arrow at the time of the eclipse.  Remember:  an ensemble forecast shows the results of many different forecasts all valid at a certain time.

10 indicates total cloud cover.  The horizontal line shows the median cloud cover for that location and the yellow box around the medium shows the range of 50% of the ensemble forecast members. (remember that the median is in the middle of a distribution of many forecasts, as many above as below).

 Lots of clouds and lots of uncertainty at that location.


Anyway, if you are planning to go to the eclipse, don't expect perfect conditions and be prepared to move, depending on the closer-in forecasts. 



5 comments:

  1. Thanks for the first look. I have been looking out to the 10 -12 day time frame and have similar conclusions.

    ReplyDelete
  2. Based on this and climatology, I think a person would need to get to SW Texas to have the best shot at seeing totality.

    ReplyDelete
  3. Could you post the light metrics before, during, and after? Those are always interesting during the dark days of Winter.

    ReplyDelete
  4. Off-topic, when is weather workshop scheduled for this year?

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  5. I think I speak for all the eclipse chasers when I ask most humbly if you would repeat this exercise on Friday so we can plan around reliable information.

    ReplyDelete

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