How Will the Eclipse Change U.S. Weather on August 21?

The total eclipse of the sun will profoundly change the amount of solar radiation reaching the surface on Monday, August 21st.  

So how will this alter the weather across the nation?  Most of the usual weather prediction models  (such as the UW WRF) will not include the loss of solar energy in their forecasts.  But fortunately, my colleagues at NOAA ESRL have for the first time included the eclipse effects in a weather prediction model...in this case the HRRR--the high resolution rapid refresh model.

To test the impacts, they ran the eclipse radiation code in a test run, using the weather situation of August 4.    Let me show you what they found--simulating for only the core hours of the event:  17, 18 and 19 UTC (9, 10, 11 AM PDT) on August 21st .

The radiation reaching the surface is shown below...the top line is using the normal (non-eclipse) radiation code.  The second line is with the case.  The bottom is the difference.  You can see a round region of profoundly reduced global radiation moving eastward across the nation over two hours.

But what about temperature?   Major cooling, with some areas cooled as much as 6°C (11°F)...but not over the Northwest, where the signal is about half as strong.   One major reason is that the eclipse hits earlier on the West Coast, when solar radiation is weaker, compared to the mid-day eclipse to the east.

What about wind?  Yes, there are effects, including effects on wind energy.  Here is the change of wind speed at 80m....near hub height of many wind turbines.  Interestingly, the wind speed effect is delayed a bit, with roughly a 1 meter per second (around 2-3 mph) reduction over the western U.S.

There have been a number of eclipse-weather studies, with documenting temperature declines at much as 15F--although in the Northwest I expect more like 3-6F in the region of totality.   So if you can, try taking temperature reading during the event and let us know what you find.

Eclipse Forecast Update

Everything looks good for the region of totality.  Best conditions around Salem (no clouds or smoke), with clear skies, with some smoke to the east.



from Cliff Mass Weather and Climate Blog http://ift.tt/2ihuLmB