We’re only 5.5 days away from the Great American Eclipse and things are looking good! It appears MOST of us in the zone of totality, where 2 minutes of darkness will pass overhead, will have a clear view of the big event. And if we forget about the eclipse for a moment…the weather itself looks GREAT across the region now through Tuesday. Are you camping? You’re in good shape…no need to worry about rain anywhere unless you get some drizzle along the coast. Aren’t you glad we didn’t tell you it was going to be a rainy/cloudy/cool eclipse with snow up on Mt. Hood? I just heard today that some of you received an alert saying that on your phones last week!
Over the past 3 days models have been advertising upper-level ridging of high pressure over our region later Sunday through early Tuesday. Of course the eclipse falls right in the middle of that time period. You can see the “ridge” in the upper-level flow over us Monday morning. The opposite would be a dip in the flow.
In this case that means a warmer than normal atmosphere over us Monday. It also means a lot of sinking motion overhead which warms/dries the airmass. Thus little or no cloud cover overhead. The ONE issue of course is the cool layer of marine air west of the Cascades. Take a look at the WRF-GFS model depiction of that marine layer (green areas) Saturday afternoon (right side) to Wednesday afternoon (left side). You can see a thin marine layer Sunday through Tuesday, then it thickens quite a bit Wednesday. Those first three days it’s no thicker than 2,000′, which means you don’t have to worry about those low clouds if your viewing location is above that elevation.
That’s pretty clear-cut, there is a high risk for morning/midday clouds right along the coastline in this pattern. As we’ve been telling you for many months, planning to view the eclipse at the Coast is quite risky. Two different models show a similar setup for low clouds Monday morning; likely at the coastline and just a possibility in the central Willamette Valley. Note the ECMWF shows some intrusion into the Portland area but not down into the valley. And you can see how the coastline is a bit iffy.