May 19, 2012

Annular Eclipe Cloud Update

Sunday noon update:  the warm front is moving through and the rain is ending over western WA.  Some breaks and thinning of the clouds can be expected during the next few hours.

An annular eclipse--the sun is not completely covered by the moon
Tomorrow (Sunday) between roughly 5:30 and 7:30 PM PDT an annual eclipse of the sun will be occurring over the U.S. West Coast.  Even if it were clear, we (Washington State and northern Oregon) would only get a partial, off-center eclipse since the prime viewing swath will be south of us (see map).

 You can go to a wonderful eclipse calculator created by NASA (found here) to see what proportion of the sun is covered and when.  For Seattle, the answer was about 83% starting around 6:44 PM (time is in UTC/GMT).

Will you see it?  I don't have particularly good news, but I can offer a slight bit of hope.

Here is the official National Weather Service sky cover forecast for 5 PM Sunday:

If this is correct, then most northwesterners are in trouble...need to head down to far SE Oregon, CA, or Nevada.  But the NWS forecasts tend to be a bit broad brushed and smoothed.  That is why you come to this blog!

What about our latest WRF weather model runs?   Here is the predicted cloud liquid water integrated from the surface to the top of the atmosphere at 5 PM and 8 PM Sunday..  Bright white would be thick clouds, gray--thin clouds.  If you believe this, there is a CHANCE for a thinning of the approaching clouds along a swatch over the southern and eastern portions of Washington. 

We can also produce a simulation of what an infrared satellite image would see if the model solution was correct.  Here it is for 5 and 8 PM.  Lots of clouds, but there some gaps and thin spots.  Forget the coast.

Finally, we have our ensemble prediction system that gives cloud probabilities.  Here are the probabilities of low clouds (surface to 3000 ft)--there still could be higher clouds above.  Clearly, the message is don't go to the coast or north.  Head south and east to improve your chances.

Bottom line:  a system is approaching tomorrow and there will be considerable cloudiness.   But there is a chance that some of you over the southern and eastern portions of the region might get lucky.   Or fly to Reno if you want to be sure!  Tomorrow afternoon go to the visible satellite animation (found here) and you will know the story.  


  1. Will enough of the sun be covered to produce noticeable darkness even if it's cloudy?

  2. Hm, I think the correct time of the start is 5:01:44 UTC -7.

    Ben from the Napavine Triangle

  3. Time to revive the K-12 math materials. My district Bainbridge Island is presenting the proposed math materials for 2012-2013 school year tomorrow to parents and the community.

    I'm just reading the email announcing the meeting and see that they chose Common Core State Standards. The textbooks are from Holt McDougal. I know about Common Core standards from from reading this blog regularly. Info from the school district at

    I'm looking for concise, relevant info on the topic that I can pull together quickly.

    Because this topic is often discussed in this blog, I thought I would ask here.

    I just joined the Facebook group for Where's the Math WA, but am unable to pose this question until I get approved.

    Thanks for help from the community. I'm just a busy parent, but I do have an undergraduate in engineering and value math and science.



  6. Although the eclipse wasn't visible from western Washington due to the cloud cover, it was visible on the NWS satellite imagery (visible) animation!


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