10:30 AM | *Two months to go to the first total solar eclipse to cross the continental US in a century*

Overview
There are now just two months to go to the first coast-to-coast total solar eclipse since 1918. On August 21st, the moon will pass between the sun and Earth and the result will be a 67-mile wide shadow that will cross the country from Oregon to South Carolina.  During a total solar eclipse (and weather permitting), the sky gets deep twilight blue, temperatures may drop noticeably, bright stars and planets come out, and animals and birds may behave strangely like it’s the end of the day.  Total solar eclipses occur somewhere on Earth every year or so, but generally cast their shadows over oceans or remote land masses.  The last time a part of the contiguous US saw a total solar eclipse was in 1979 and the next total solar eclipse on US soil will take place in April 2024.

Discussion
The last total solar eclipse in the contiguous United States, 38 years ago, only clipped the northwestern United States, mostly rural areas of Washington, Oregon, Idaho, Montana and North Dakota. And on that particular day, Feb. 26, 1979, it was cold and dreary in the Northwest, and most people in the path of totality did not even see the eclipse due to clouds and rain.  On August 21, 2017, millions of Americans will witness the moon moving in between the Earth and the sun to create a total solar eclipse. This spectacular phenomenon occurs when the sun, the moon, and the Earth line up in a row, causing the moon to cast a shadow over the planet.

On August 21, 2017, the moon will pass between Earth and the sun in a total solar eclipse that will be visible on a path from Oregon to South Carolina across the continental United States. Map courtesy NASA

The 67-mile wide path of the moon’s umbral shadow will begin in the northern Pacific and cross the U.S. from west-to-east through parts of the following states: Oregon, Idaho, Montana, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, and South Carolina. It will pass directly over cities such as Salem, Ore., Idaho Falls, Lincoln, Neb., Kansas City, Nashville, and Columbia and Charleston, S.C. Places within a one- or two-hour drive of the eclipse include Portland, Ore., Boise, Cheyenne, Rapid City, Omaha, Neb., Topeka, St. Louis, Louisville, Knoxville, Chattanooga, Atlanta and Charlotte. At any given location, the total eclipse will last for around 2 or 3 minutes turning day into a dark twilight and the total event will take about three hours from start to finish. The moon’s penumbral shadow produces a partial eclipse visible from a much larger region covering most of North America.  

Close-up view of percentage totality in the Mid-Atlantic region with the 80% line cutting right near the Philly metro region

In the DC-to-Philly-to-New York City corridor, the duration of the solar eclipse will be about 2 hours and 40 minutes.  The beginning of the solar eclipse in this corridor will be around 1:20 PM (ET), the time of maximum coverage of the sun around 2:45 PM (ET), and the ending time around 4:00 PM (ET).  The percentage totality will be roughly 84% in the DC metro region, 79% in and around Philly, and 77% in and around the NYC metro region.  

This total solar eclipse will provide a rare opportunity to study the sun's wispy outer atmosphere called the corona. The sun's overwhelming brightness usually drowns out the faint corona and not even a 99 percent eclipse will reveal the sun’s corona - it must be total. Temperatures in the corona top 1.8 million °F (1 million °C), making the region much hotter than the solar surface, which is just 11,000 °F (6,000 °C) or so. How the corona gets so hot has puzzled scientists for decades and solar scientists aim to gather some useful data during what is now being referred to as the "Great American Solar Eclipse".

This map shows the path of totality overlaid on a statistical map of cloudiness for the month of August where the best places to be are blue. Courtesy spaceweather.com and meteorologists Jay Anderson, Jennifer West

Based on historical data from NASA's Terra and Aqua satellites, the best place to view the solar eclipse from a statistical viewpoint is in the interior western US (blue areas on map) where fractional cloud cover dips as low as 15%. In general, cloud cover becomes more of a problem east of the Mississippi River and it can be problematic along both immediate coastlines.  From a meteorological point of view, one thing to monitor as we approach the August 21st time period will be tropical moisture to see if it could play a role in cloud cover across the southern and/or eastern US. The Atlantic Basin tropical season will be well underway by this time and a tropical system could wreak havoc on a large area in terms of cloud cover. Make your plans now and hope for good weather....just two months to go.

Warning: Never look at a partial solar eclipse without proper eye protection. Looking directly at the sun, even when it is partially covered by the moon, can cause serious eye damage or blindness. 

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com