NOAA scientists get rare chance to study the effects of an eclipse on weather

It’s the most fundamental principle of meteorology - energy from the sun drives Earth’s weather.

So what happens when the sun’s rays are blocked by an eclipse? And can modern forecasting tools accurately predict changes in the weather when the sun’s rays are partially or totally blocked?

On August 21, NOAA scientists are going to find out.

With the help of an algorithm developed by a team from the University of Barcelona and the National Center for Atmospheric Research, researchers at NOAA Research’s Global Systems Division will use an experimental version of the High-Resolution Rapid Refresh (HRRRx) short-term weather model to attempt to predict subtle changes in the weather caused by the moon blotting out the sun - changes that current forecasting models are not equipped to handle.

“The sun does drive the weather daily and is fully predictable,” said Stan Benjamin, a NOAA senior scientist. “But we’ve never tried to code an astronomical event into an experimental real-time weather forecast model. For us, capturing the subtle effects of an eclipse in a model is like frosting on a cake enjoyed only on rare occasions.” 

Wait ... an eclipse can change the weather?

For most eclipse-watchers, the one burning question will be: Where will the clouds obscure a view of the eclipse? Meteorologists and weather modelers will have different questions, like how will the eclipse affect temperature, or the speed and direction of low-level winds? Will the loss of sunlight affect weather events in progress, such as thunderstorms?

As the path of totality sweeps across the United States from Oregon to South Carolina, the HRRRx will be fed weather data from NOAA’s weather observation network, ranging from temperature, humidity, wind speed and direction, clouds (from satellite and surface) and radar. A simulated run of the HRRRx earlier this month suggested temperatures could drop up to between 5 and 12 degrees Fahrenheit under clear skies, with effects on wind becoming apparent up to two hours after the moon’s total shadow passes.

The eclipse will give NOAA scientists an unprecedented opportunity to compare conditions of the atmosphere with and without the eclipse, and see how it interrupts processes in the lowest part of the atmosphere in direct contact with Earth’s surface across the entire continent

Weather forecasting has undergone several technological revolutions since February 1979, the last total solar eclipse in the US. NOAA now has weather models that are precise enough to usefully predict weather impacts from non-meteorological events like the smoke from wildfires or volcanic ash plumes.

“We couldn’t have done this at all 40 years ago,” said John Brown, a NOAA meteorologist. “Before the HRRR came along, we could only have done this crudely at best.”

Measuring eclipse effects for future study

To validate the HRRRx forecast and to better understand the eclipse’s effects, researchers from the NOAA Research’s National Severe Storms Laboratory and partners will deploy a truck equipped with surface instruments, launch weather balloons, and fly two unmanned aerial systems to record the atmosphere during the event. Meteorologists will measure surface temperature, relative humidity, wind speed and direction, pressure and solar radiation every second from a location in the path of totality.

In Oak Ridge Tennessee, the Atmospheric Turbulence and Diffusion Division of NOAA Research’s Air Resources Laboratory will use a small drone and weather balloon to capture weather data before, during and after the eclipse. Those observations will be added to data from 13 U.S. Climate Reference Network Stations collected by NOAA’s National Centers for Environmental Information and made available to researchers.

More information:

To see real-time HRRRx forecasts, visit https://eclipse2017.noaa.gov.  Forecasts showing the effects of the eclipse will begin appearing Saturday evening.

Media contact: Monica Allen, NOAA Communications, (301) 734-1123 or monica.allen@noaa.gov.