Eclipse Weather: A First Look

August 13, 2017

10pm Sunday

Now that we’re within 8 days of the eclipse, we can start to see a general weather pattern emerging.   The good news is that we don’t see a big wet weather pattern for next weekend and early the following week.  The (possibly) bad news is that SOME models keep trying to send a weak front or upper-level low quite close to us.  Of course that could possibly send lots of cloud cover overhead at the wrong time (for example…10:20am Monday the 21st).

Let’s check out the big picture:

  1. We don’t know YET if large parts of the Pacific Northwest will be covered in clouds OR just under high pressure with mainly sunny skies.
  2. Both of those possibilities (or perhaps something in-between) are still in play.
  3. There is no need to worry, or freak out, no matter where you area headed this weekend.  We’ll get a more detailed forecast as we go through the week.
  4. Do NOT alter your plans or viewing for now.  I know the hardcore folks have plans to move at the last minute if needed.  Don’t worry about that yet.

The general weather pattern for this calendar week is high pressure moving back over the West Coast, but this time it won’t be a big hot ridge of high pressure.  A weak jet stream will be just to our north later this week and through the upcoming weekend.  This is typically a nice weather pattern with varying amounts of morning clouds west of the Cascades.    On most models this continues through the early part of next week.

But SOME runs of SOME models have been trying to push a weak cold front or even an upper-level low through our area either Sunday or Monday.  The (less reliable) GFS model has been most persistent with this idea.  Take a look at its forecast for eclipse time in 8 days…very bad with a cold front moving onshore…solid cloud cover west of the Cascades, but just high clouds east of the mountains.

 

But then check out the ECMWF model:

Totally different with that weather system both staying to the north and also splitting apart well offshore.  This would say great viewing for the big event.  You can see why it would be a really BAD to make a specific cloud forecast at this point.

So is there anything else we could use to get an idea which model might be wrong, even this far out?  Yes, as I’ve mentioned in the past “ensemble forecasting” can help us out.  Take a look at the ensemble forecast from both the GFS and ECMWF for next Monday at about 18,000′.

You can see the GFS in general has slightly lower heights (more members that are giving us stronger upper-level troughing).  That said, even that 2nd map isn’t a wet or especially cloudy weather pattern.  Check out the GFS ensemble member rain accumulation forecast, each horizontal line representing one of those 21 members:

I see 5 members with a trace or more rain on eclipse that.  That’s about 1/4 of the members.  Obviously if we have rain there is cloud cover as well.  So it’s fair to quite a few members of this model have cloud cover over us on the big day.

How about that ECMWF?  The operational run of that model as you’ve seen above is quite nice.  Now look at the 51 ensemble members and their rain forecast:

Again each horizontal line represents one ensemble member.  I see 6 or 7 ( I also looked at all 51 maps!) members that would give us lots of clouds and even showers.  That’s a small percentage.  Odds are, based on this model, viewing might be just fine…but again it’s 8 days away.

One other model, the GEM (Canadian) looks pretty good as well.  It shows no sharp upper-level trough and just continues our fair weather pattern.

Of course I’ll be keeping on top of it all week-long.  I’m working each day through the eclipse…that last 2-3 down in Madras.

Chief Meteorologist Mark Nelsen


It Rained! Now Keep Watering Your Plants

August 13, 2017

5pm Sunday

I was camping with the family out at Stub Stewart State Park the last two days (very nice mountain bike trails!), and right at bedtime last night it started raining.  It was a rare summer sound to hear it raining all night, although I doubt it would have been real fun in a tent (we use a pop-up trailer).  Quite a change.

So of course the overnight rain ends our long dry spell in Portland.  This was the longest dry spell since the early 1980s in Portland

Brian Longest Dry Spells

Mark Dry Spells Summer Recent

We ended up with .06″ rain in Portland; just barely enough to settle the dust

2017 Data Bound Rain Today in Metro Only

Notice EVERYONE saw the rain west of the Cascades, just not a lot.  I’m pretty sure the Scappoose reading is incorrect since several stations within 1-5 miles had measurable rain.

We would need an inch of rain to even call it a “soaking” and what little we just had doesn’t go far into the ground.  So your plants/gardens/trees barely noticed.  Keep watering because we don’t see a soaking rain for at least the next 7-10 days.

The westerly flow and weak front have given us 3 big changes:

  1. No hot weather, today’s high of 75 was the coolest in almost a month.  We remain below 85 for the next week.
  2. Fire smoke is gone…it has moved east of the Cascades
  3. Humidity is back to normal.  After a week or so of humid weather, dewpoints are back into the 50s, a big improvement!

I’ll have another post later on eclipse weather…it’s only 8 days away now.

Chief Meteorologist Mark Nelsen