A Historic Early April “Heat Wave” On The Way

Get ready for record breaking warm (not really hot) weather the 2nd half of this week!

This morning we are under a cool and showery airmass, with snow levels down around 4,000’…that’s quite a change from the past 5 days!  This is a quick-moving cool airmass and it’ll be mainly gone by Tuesday evening.  Then things get real interesting as a pattern we’ve never seen so early in the season develops…


  • Wednesday-Friday will each likely set a record high temperature in Portland (records: 78, 79, 74)
  • The warmest weather we’ve ever seen this early in Spring is coming for one day…Thursday
  • Most likely high temperatures will be in the 85-90 degree range in the western valleys on Thursday
  • The coast should see 70s and a few 80s Thursday (one day only)
  • This isn’t really a heatwave (temps remain below 90), but it IS unprecedented for the first week of April in our area.
  • Confidence is unusually high for this event as all models are in agreement


What’s going on?

A big ridge of high pressure develops right over the West Coast Wednesday and lingers through Friday.


It happens pretty quickly with the highest upper-level heights over us on Wednesday.  At that time models are in very good agreement showing 500 millibar heights around 584 decameters (5,840 meters) over the Salem sounding location.  Taking a look at the SPC website showing historical soundings:


notice the yellow area is the forecast, and the red lines are the highest number we’ve seen for each date in the past…we’ve never seen heights this high in early April!  As the ridge moves slightly east Wednesday night and Thursday, upper-level flow goes southerly (warm!) and the low level flow turns sharp easterly.  The WRF-GFS surface map for Wednesday PM shows north/northeasterly flow:


and then straight east wind midday Thursday:

WRF_ThuMiddayOnshore flow in the valley does not kick in until Thursday evening/night.  As a result we get maximum warming under full sunshine both days.  It’s a relatively easy forecast, since models are in great agreement.

Then the next question is “how warm could it get?”  Hard to believe I see these numbers in the first week of April:  All models are right around +18 to +19 degrees Celsius at 850 millibars.  That’s upper 60s at 5,000′ in the atmosphere overhead!  Take a look again at the SPC sounding climatology and you see how far out of the norm this is going to be (in yellow):


Crazy isn’t it?  We haven’t see 850mb temperatures this warm in our history until about 3 weeks from now!  And remember the red line is highest on record.  The normal isn’t even visible on the chart.  The atmospheric temperature overhead will be above normal for even July/August in our area.

As a result, the extremely high (for early April) temperature forecast is a bit tricky.

At this point, if it were the last week of April, I’d forecast 90 degrees for Thursday.  Instead, accounting for lower sun angle a few weeks earlier, we’ll go for somewhere in the mid-upper 80s.  That’s still 25-28 degrees above normal!  Wednesday will be somewhere around 78-81, and Friday with stronger onshore flow should quickly push us back down below 80, so the extreme temps are just for the one day…Thursday.

Chief Meteorologist Mark Nelsen

31 Responses to A Historic Early April “Heat Wave” On The Way

  1. MaryDee says:

    My son in SW Ohio reported blizzard conditions last weekend, with temps down to the mid 20s F. All the blossoms on his blooming fruit trees have turned brown and fallen off. The forecast for this weekend is for temps down to 19*F. That will kill the leaf buds, too!

  2. Jason Hougak says:

    🎶No… no… heat… heat… till summer… summer 🎶 No… no… heat… heat… till summer… summer🎶

  3. Very light rainfall has begun here for the past 60 minutes or so. It appears now as if the “heat wave” will not be as warm in my area as earlier forecast. could see it up to 72F or so on Thursday which is till pretty warm, but not record breaking.

  4. Mike says:

    It was surprising to travel thru North California and see the vast areas of dead decidious trees. I have never seen that before. I’m glad the evergreens survived.

  5. Joshua Downtown PDX says:

    This upcoming heat wave really sounds ridiculous when you look at the cool spell equivalent. We would be looking at highs of 38, 34, and 41 for Wednesday, Thursday, and Friday based on the anomalies compared to normal and Mark’s forecast. Can you imagine that? Me neither, but is sure seems to be possible to have these crazy warm anomalies time after time.

  6. Paul D says:

    Mark says it’s not a heatwave because it’s below 90, but this is APRIL!! It’s a heatwave, and I’ll be inside running my A/C.

    Two record breaking February’s, warmer than normal winters, record breaking heat in April, it all really makes you wonder if it’s the new normal (which would completely suck).

    Those kind of temperatures are for August, not April. 😦

    • pappoose in scappoose says:

      True it is! (heatwave)

    • Mark Nelsen says:

      Or you could just open a window in the morning when it’s 45-55 degrees?

    • Anonymous says:

      That’s too simple a solution Mark, it’ll never work. Besides, it’s contradictory to Paul D’s pension for whining about outdoor temperatures over 60 degrees.

    • W7ENK says:

      That’s too simple a solution Mark, it’ll never work. Besides, it’s contradictory to Paul D’s pension for whining about outdoor temperatures over 60 degrees.

    • W7ENK says:


      I commented once, it asked me to log in to WordPress, took me back to the page and my comment was still typed into the comment box. Not posted, I clicked the button again.

      Apparently it went twice?

  7. Farmer Ted says:

    This will be a little unusual but not all that out of the ordinary for my area here at Barton. My rule of thumb is as follows:

    March 1st possible for 70 degrees
    April 1st possible for 80 degrees ( have had a lot of mid 80 degree days in April over the years)
    May1st possible for 90 degrees (I have seen 100 degrees here around mid-May)
    June 1st possible for 100 degrees
    4th of July rain showers and 60 degrees!

  8. Jason Hougak says:

    Don’t need the heat, too busy at work and water needs only become more urgent the hotter it gets. All those plant nurseries really freak out when their water wells stop flowing.

  9. karlbonner1982 says:

    When are we gonna have another post with the ECMWF Weekly maps? I’m dying to know what the 2nd half of April might look like….

  10. runrain says:

    Looks like we overachieved a bit on the high today. Currently 61 after expected mid-upper 50’s.

  11. I’m waiting to see how it develops. Being further north, I don’t believe it will touch 80F here, but we’ve been close before. Back on april 11, 2004 I saw the temperature reach 79F.

  12. Hal in Aims says:


  13. runrain says:

    Wonder if this is the year for that elusive 108 deg record. What the heck – maybe 110??

    Has anybody purchase a bat house (a house for bats)? Could be nice to have them around to pick off the mosquitos this summer. Just don’t want any rabies risk in the process!!

    • Hal in Aims says:

      had one for a couple years……bats never used it…..but they sleep somewhere ’cause as soon as the swallows go off duty…the bats go on duty …..

    • oregonalex (Rock Creek, 240 ft) says:

      I had a bat house for a few years and they never used it either. They have, however, roosted in a folded garden umbrella over our picnic table. Go figure. They produce prodigious amounts of guano – choose the siting of the bat house with that in mind. As you can imagine, bats in an umbrella above a table – not pretty.
      Rabies is not an issue unless you handle them with bare hands and happen to get bitten by an infected one. So don’t handle them and you’ll be fine. We love having them around…

      Now if I could also attract anteaters to our back yard…

  14. WEATHERDAN says:

    Why wait until Wednesday for the big warm up. According to local NWS obs, at 10:00 AM Salem is 194 degrees with 1% humidity. Your tax dollars at play. Peace.

  15. Mark bergal says:

    And its only us. Most of the country, including calif, stay at or below average. Our region is heating up faster and faster for whatever reason. We need to face we are becoming a part of the sun belt. Highs in the 100s, during the summer, will be normal.

    • W7ENK says:

      Okay, now that’s just plain paranoia. In our climate, 100+ is very, VERY hard to achieve, which is why it’s such a rare occurrence… Kinda like snow!

    • Boring Oregon says:

      W7ENK that’s not paranioa, that’s facts. If we have one warm week in April it clearly means that 100+ days will be normal in the summer and Climate Change will kill us.

  16. W7ENK says:

    I can’t wait!! 😀

  17. Joshua Downtown PDX says:

    Lucky us. Looks like the uncomfortably warm weather window is ever-increasing here. Last year, summer essentially started in April. Looks like it will again this year.

    • I hope not. That early start to summer is a big part of what made July so dry. There would have been a lot of dead trees on the island if it weren’t for several good drenchings in August. A few died as it was.

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