What Will the Weather Be on the Day of the Total Solar Eclipse?

With less than a month to go to the eclipse, emotional temperatures are starting to rise. Like a good murder mystery, suspense is building as we get toward the last chapter. And, like many of you, I’m wondering how the spring is shaping up — in particular, has it been cloudier or sunnier than normal so far? And how does that bode for weather on the day of the eclipse?

Cloud Cover: A Clearer Early Spring

I went back to the NASA cloud datasets to find an answer. February cloud statistics became available on March 10th, so I made the map below. It shows the departure from normal, that is, how this February’s cloud cover differs from the average of the last 20 years (2004-2023) of Februaries. It has some interesting features.

Over much of the path of totality, from northern Texas northward, the weather has been sunnier than usual this past February — and sunnier by quite a bit through Indiana, Illinois, and Ohio. In southern Texas and Mexico, it’s been pretty close to average.

It’s difficult to put these observations into perspective, as cloud cover is a highly variable parameter, and this map needs more sophisticated statistical treatment to show that it’s not just a random variation. However, the large regional coherence in the area of lower cloudiness, which covers much of eastern North America, suggests that the clearer skies are a real feature of the month’s weather.

How this observation from February’s data translates into April’s weather, especially April 8th, is a big question mark, but at least it’s not a discouraging climate signal.

Weather Forecasts

Now that we’re approaching eclipse day, it’s time to abandon long-term statistics such as those found on my website, eclipsophile.com, and look instead to actual forecasts of eclipse-day weather. Forecasts depend on numerical (computer) models and the best of these only attempts a prediction from about 15 days out — so, March 24th becomes that magic day. However, it would be surprising if 15-day forecasts turned out to be spot-on when eclipse day arrives. Look if you must, but be a skeptic until April.

Computer forecasts come in two flavors: long-range global and short-range regional models. While there are many long-range forecasts — more than 30 — you might want to confine your attention to one of these three: the American GFS model, the European ECMWF, and the Canadian GDPS. Of these, the ECMWF is generally regarded as the best performer, but I suggest that serious umbraphiles monitor all three if caught up in the eclipse passion and have extensive travel plans.

There are many places online to get model outputs. The cloud forecasts will be the same from site to site, though their presentation colors may be different. Here are a few that I have looked at:

• The storm-chaser site at the College of DuPage, (https://weather.cod.edu) probably updates more quickly than the others but doesn’t offer the ECMWF model.
• https://weather.us gives access to more than a dozen models, including the ECMWF and a high-resolution GFS (GFS .125). The site has an odd depiction of cloud (black clouds, yellow for clear skies) that can be a bit confusing at the start.
• Pivotal Weather (https://home.pivotalweather.com) offers all three of the long-range models and many more, but watch out for the colors used: cloudy areas are blue and clear areas are white.
• Windy (https://windy.com) has been a favorite with eclipse chasers in the past. It has a limited set of models, but the important ones are there. Windy allows you to compare spot forecasts from all of the models on one page.

Planning for Eclipse Day Weather

At 10 days out, forecasts will have some areas of agreement — and many where they differ. For example, in the figure below, we see two 10-day forecasts, the ECMWF and the GFS, from Windy’s site. The position of the cold front angling offshore is fairly similar between the two. The spring storm south of the Great Lakes is much more dramatic in the ECMWF than in the GFS, with a major impact on eclipse-viewing choices. On the other hand, the two forecasts agree that much of Texas will be looking good.

Can you trust the two models to be correct in the areas where they agree and head to Arkansas? No, you can’t — but wait four days and look again. If the later six-day forecasts are similar to the previous 10-day ones, then you can start making early plans. Comparing the same model over time can help identify areas where the forecast is persistent. When evaluating models for forecast reliability, look both for consistency between models and a similar forecast from day to day in the same model. Typically, you will see the numerical forecasts come together two or three days ahead of April 8th, giving enough time to get on site and avoid the heavy traffic of eclipse morning.

Once eclipse day is in sight, the short-range models will come into play. These models have more sophisticated calculations and higher resolution, but they only go forward about 3½ days. The most popular models are the American NAM and the Canadian RDPS, but there are others that can be explored at the site you choose. Stay cautious about the forecasts and try to select areas with consistent predictions of sunny skies and head for your eclipse site.

If, on April 7th or even on the morning of eclipse day, April 8th, you still aren’t sure what the weather will offer, it’s time to switch to satellite images to find that nearby hole in the cloud. Hopefully, there’s one nearby!

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