At a Glance

It's not possible to forecast weather this far in advance of the August eclipse.Average weather conditions tell us this is nearly an ideal time of year to keep weather from blocking the view.

The odds are good that weather won't get in the way of.

A narrow swath from Oregon to South Carolina will see the moon completely mask the sun on Aug. 21. Nearly all other parts of North America – as well as parts of South America, Africa and Europe– will also see at least a partial eclipse.

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The eclipse will start mid-morning in the Pacific Northwest, around midday in the nation's heartlandand early-afternoon in the Southeast, ending in the Lower 48after 4 p.m. EDT.

NASA data visualizer Ernie Wright created this map which shows the path of the upcoming Aug. 21 total solar eclipse. Total coverage of the sun is shown by the light gray strip.

(NASA)

To be clear, it is far too early for us to make a credible, specific forecast for any location on Aug. 21. However,average August weather conditions over many years providesome perspective on the chance rain or cloudiness could block your view.

Rain Chance

, an Alaska-based climatologist with the Western Regional Climate Center, constructed several maps which lend some insight into typical August weather.

The first map below shows which month of the year is typically the wettest.

Areas in the maroon shading, from parts of the Great Lakes and northern New England to the mid-Atlantic and Southeastern seaboard, including parts of Florida, to a swathof the Desert Southwest, southern Rockies and much of Alaska, typically are wettest in August.

The map above shows which month is the wettest, on average, based on 1981-2010 data from NOAA's National Centers for Environmental Information. Areas in dark maroon are typically wettest in August.

(Dr. Brian Brettschneider/WRCC)

That doesn't sound like good news for eclipse viewing.

However, let's examinea better proxy for typical rain chances – namely, the average number of days with measurable rain in August.

Average number of August days with measurable precipitation with the Aug. 21, 2017 solar eclipse's path of totality overlaid.

(Dr. Brian Brettschneider/WRCC)

Given the summer dry season, the Great Basin and West Coast havethe best chance of a dry August day. Even Texas and southern Oklahoma only see measurable rain once every six to 10 August days. Most of the rest of the central U.S. only records rain every three to six August days.

In the Great Lakes, southern Rockies, Appalachians, interior Northeast, parts of the Southeast and northern Gulf Coast, rain is a bit more common, occurring every two to three August days.

Therefore, in all these areas above, your chance is better you'll see a dry August day than a rainy one.

One exception to this, however, is the Florida Peninsula, where afternoon thunderstorms can almost be a daily occurrence in summer.

What About Those Summer Thunderstorms?

A singlethunderstorm won't last long enough to affect the entire 2- to 3-hour viewing period of the eclipse.

An example of a mesoscale convective system, or cluster of thunderstorms, responsible for flash flooding along the northern Gulf Coast on April 30, 2014. Infrared satellite image and 15-minute lightning strike data (teal blue minus signs and red plus signs) is shown.

(UW-CIMSS)

However, one of these stray thunderstorms could be so poorly timed it occurs over part of the area seeing an eclipse for the roughly 2- to 3-minute period of totality.

This is likeliest on the far southeastern U.S. leg of the total eclipse area, where total coverage of the sun occurs between 2 and 3 p.m. EDT – roughly the time of daypop-up afternoon thunderstorms typicallyflare up.

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Posing more of a threat to block out the eclipse, clusters of thunderstorms known as are common in the summer. Their rain or cloud shield can linger over a given location for more than an hour.

However, these clusters are typically more active during the nighttime and early-morning hours – not necessarily during the early-afternoon hours, whenthe August eclipse will occur in the central and eastern U.S.

What About Cloud Cover?

Of course, all you need are stubborn, sufficiently thickclouds to block your view of the eclipse, even on an otherwise dry day.

There issome good news: according to Dr. Brettschneider's March 2015 blog, .

In most of the nation, average afternoon cloud cover in mid-late August is less than 50 percent.

Average cloud cover (percent) at 2 p.m. EDT from August 14-28, based on 1979-2016 ERA-Interim data from the European Centre for Medium-Range Weather Forecasting.

(Dr. Brian Brettschneider/WRCC)

August doesn't typically feature the large, strong frontal systems known by meteorologists as extratropical cyclones, producing not just widespread precipitation but also clouds that coversometimes a dozen states or more. These happen most oftenfrom late fall through the middle of spring.

Also, some of the typically cloudier locations in the U.S., such as the Great Lakes, New Englandand the Pacific Northwest, aren't as cloudy in August.

If this eclipse happened inNovember or December, for example, there would be a higher chance of eclipse fans disappointed by a stubborn cloak of clouds.

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Visible satellite image of Hurricane Irene on Aug. 28, 2011, at 8:32 a.m. EDT, just 28 minutes before landfall in Brooklyn, New York.

(NASA)

One wildcard to all this is tropical cyclones.

Upper-level windscan spread a canopy of clouds over areas far from the center of a tropical storm or hurricane.

Just the remnant moisture of a former tropical storm or hurricane can either trigger more numerous thunderstormsor can, again, block out the eclipse with its clouds.

This can not only occur in the eastern and southern U.S., but also with remnant eastern Pacific tropical cyclones in the typically sunnier Desert Southwest.

Again, we have no way to forecast exactly what weather features will be in place this far in advance of the historic total solar eclipse. However, this is about as close to the sweet spot of typically optimal viewing weather one can get for much of the country.

Be sure to check back frequently for complete coverage of the historic August 2017 total solar eclipse.

Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him onand.

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