A Warm and Sunny Weekend Ahead? Probably Not!

I was on forecast duty early this afternoon after barely looking at maps the past two days.  Some minor changes in the general weather pattern over our region means a major change to the extended outlook.  3 days ago I was thinking 70s were very likely this coming weekend.  Of course that wasn’t within the 7 Day forecast at that time so you never saw them  in a forecast graphic.

For those just tuning in for the basics:

  • More clouds than sun this week
  • Rain is most likely on Friday
  • Showers are possible again tomorrow afternoon, late Wednesday, or early Thursday.
  • This weekend’s forecast is very much up in the air, models are all over the place beyond Saturday.
  • I’d put a couple of big question marks for Sunday and Monday, but that doesn’t make for good TV.
  • In general, temperatures will be warming a bit the next 7-10 days.

The big change in the maps/models compared to what I saw Friday?  A building upper level ridge late this week is much flatter (heights are lower), and slightly farther offshore.  Sound familiar?  This is a similar setup to the pattern we have seen several times since early January.  One in which weak disturbances ride over the top of the ridge and then scoot across the Pacific Northwest.  They are quite weak, but northwest flow running into the Cascades is quite efficient at squeezing lots of moisture  out of the clouds and keeps us gray here in the lowlands.  That seems to be the case from late Wednesday through at least Saturday.  Interesting that a setup like that keeps reappearing.

Of course with an upper-high just offshore, slight variations in the position make for a huge variation in our weather.  If the ridge is a little closer we get very sunny and warm spring weather.   Position it farther offshore and we get onshore flow/showers with a surface high to our west.  Here’s a good example of the variation on the 12z ECMWF ensemble chart:


Remember the blue line is the operational run that we all get maps/data for.  The red line is the average of all 51 ensemble members.   Good general agreement through Saturday the 20th (the line “21”).  Then they diverge wildly.  Just two days later, they are anywhere from a -4 at 850mb (similar cold temps that we’ve seen the last two days) to a +14 (high temps well into the 70s or even 80).  The ensemble mean and operational are both around +4 at that time with lots of cloud cover and showers just to our north.  The 12z GFS is similar:


a wide spread after Saturday.  The 18z GFS was even cooler and wetter, although that run was nearly the coldest of its ensemble members from Sunday through most of next week.  Then it swings way up to the warmest beyond that point.


This is a good example of how you can use ensembles to forecast…in this case it’s probably safest to go for a “middle ground” until models calm down a bit and settle on a reasonable solution.

One item hasn’t changed on the ensemble average on all three charts the past few days:   Upper level temps are generally average to above average starting Thursday through most/all of the extended period.  We’ll see if that holds in the coming days.

Chief Meteorologist Mark Nelsen

35 Responses to A Warm and Sunny Weekend Ahead? Probably Not!

  1. WX Ninja says:

    Mark and his warm bias are showing on the 7 day…or is it cold bias???

  2. Sifton says:

    My wish cast is winning again!! OH YEAH…………

  3. Euro is back with the goods by next week.

    • Mark Nelsen says:

      Our low 70s forecast for next Monday-Tuesday is very conservative too. If the ECMWF is correct we’ll be around 80 on Tuesday.

    • JJ97222 says:

      That is great news just beautiful out there today boy, the guy just got the garden is tilled up maybe the sun will rule this weekend after all. I new you could get us some dry weather Mark. Just think about all of the outdoor activity, that is something to get teed off about foooouuuurrrr!

    • High Desert Mat says:

      Believe it when I see it. Here in Redmond I’ve woke up to snow on the ground last three mornings. Grrr. Ready for some warmth. Raw outside last few days.

  4. JJ97222 says:

    Hey kgw has 70s on the board can you believe it are swinging the other way now lets see who wins out!

  5. Jesse-Stevenson says:

    Yay! Glad to hear we will get some more needed rain. 🙂

  6. There was fog again this morning but it quickly cleared and now the sun is out.

    Low of 36 this morning.

    The average last frost for my station here is May 4th, so we shall see when this year’s actually occurs or occurred.

    • JJ97222 says:

      The sun was out and now it is raining again but wait blue sky trying to come back but now the clouds are winning it is like the casino will always win by house rules. PNW clouds and rain always win. The odds are not on your side to go outside without getting wet and cold. It is cold out this morning I cancelled my guy to till up the garden for our new home owners I guess they will have to deal with it in July.

    • bgb41 says:

      32.5 out here this morning. 2nd morning in a row with light frost.

    • W7ENK says:

      Yes, I also noticed a very light frost on the tops of cars with fog this morning as I was walking to the bus. More reminiscent of mid/late October.

  7. chiefWright (Marquam) says:

    I’ve always wondered if there’s a way to graphically show the level of uncertainty in an extended range forecast. Like right now the uncertainty 7 days out is pretty big. But other times of the year the certainty is pretty darned good. I bet it the uncertainty can even be consistently quantified (OK, you non statisticians are thinking I’m a dwerb. Mea Culpa). I would actually much rather see a range rather than a single point 7 days out. Is there any way to simply illustrate the quantifiable uncertainty?

    • Mark Nelsen says:

      Yes, but higher ups would definitely not like it. That’s the main reason we don’t do it. If you are watching the show, the meteorologist/weatherperson SHOULD be verbally making it obvious.

    • WestVan says:

      As you already know. I would love it. It would be a more accurate forecast. It would be more honest. So there’s another vote for uncertainty in the graphics when appropriate. 🙂

  8. Kent Estep says:

    Pretty cool sunset tonight as the cell to the northeast of Portland slowly broke up…


    Also took a couple of time lapses over the weekend…

  9. Springtime in the PNW. Looking several days down the road is like looking outside right now. One moment it’s clear and dry and the next it’s pouring down rain and hailing. But wait!! Next it’s sunny again!

  10. runrain says:

    Nice splattering of hail over by the Rose Garden about an hour ago

  11. Dave in SW PDX (235') says:

    Dammit! I was hoping for another warm & sunny weekend, but it’s been gradually slipping away. Thanks for breaking it to us gently, Mark.

  12. Aleta- West Gresham says:

    So much for mowing this weekend!

  13. bgb41 says:

    What a huge change last three runs of the GFS. I suspect the pessimistic outlook of the 18z will improve at least a little with the 00z run later this evening.

  14. The sky looks like the mid-west! Nice towering clouds and anvils.

    46 degrees though, that’s very unlike the mid-west!

    • Dave in SW PDX (235') says:

      The sky definitely has “that look” to it. Interesting watching the unusual N to S movement of the clouds.

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