Watching the cloud forecast for Monday is like watching the snow forecast for an upcoming powder day.
1) I start with no confidence
2) As the time gets closer I gain confidence
3) Within a few days of the event, new wrinkles are thrown in which make me lose a bit of confidence
4) About 24-48 hours before the day, the picture becomes more clear
Right now I am around step (3). We have a decent handle on the overall weather pattern for Monday, but there are some new wrinkles, so confidence is still not super high.
The cloud forecast for Monday
Here are the cloud forecasts from two different models. The white color shows areas of forecasted clouds, and the red line is the path of the center of the eclipse.
There are differences in the models, which is to be expected when we attempt to forecast clouds 3 days in advance.
The takeaway from the two images above is that both models agree that Oregon will be clear. The models do not agree on much else.
Things to watch for on Monday
There are two weather-related features that should produce clouds on Monday.
The first weather feature will be a push of moisture which will result in high clouds streaming from the southwest to northeast, generally over Colorado toward the southern half of Wyoming and over to Nebraska.
High clouds could simply filter the sun a bit and could still result in a decent view. Or, if these clouds are a bit thicker and we add in some mid-level clouds, then the sky could be rather overcast.
The second weather feature is a weak system over the northern Rockies moving from west-to-east. This is the new wrinkle in the forecast which I did not notice in previous models.
There will be a small area of mid and high-level clouds associated with this system, which could also obscure the sun. The models do not have a good handle on the timing. Does the system move more slowly and these clouds hang over Oregon or Idaho? Does the system move more quickly and clouds clear Oregon and Idaho and linger over Wyoming? I have no idea.
If you want to play the odds of completely clear skies, I'd head toward Oregon. If don't want to adjust your target and plans are taking you toward a potentially cloudy location, don't panic. There could be breaks in the cloud cover and you might get lucky.
Perspectives from other meteorologists
Dr. Cliff Mass is picking Oregon. Here's why:
Dr. Jim Steenburgh, otherwise known as Professor Powder, reminds us that cloud forecasting is hard and not to take any cloud forecast too seriously. http://wasatchweatherweenies.blogspot.com/2017/08/potentially-harsh-realities-of-eclipse.html
Dr. Steenburgh also lists some useful cloud-forecasting tools here: http://wasatchweatherweenies.blogspot.com/2017/08/forecast-outlooks-and-products-for.html
Meteorologist Mike Smith shares a story of chasing a 1991 eclipse to Hawaii only to have it rain: http://www.mikesmithenterprisesblog.com/2017/08/what-happen-if-it-rains-during-eclipse.html
I'll post again on Sunday, assuming that the upcoming eclipse doesn't encourage our first child to exit the womb a few days before his official due date of August 25th:-)
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