Spring Break, A Tornado, & Wet/Dry Parts of Metro Area

9:30pm Sunday…

Ahhh, spring break in Oregon. One thinks of…exactly what our 7 day forecast shows. A mix of cool, showery days plus some warm sunshine too.

It’s raining this evening as a cold front approaches the coastline.

The front should pass by Astoria by midnight, then through the metro area sometime between 2-4am. Behind this front the steady rain changes to our usual “sun & showers” spring weather pattern. Tomorrow won’t be all that wet, just light showers that come and go. Snow levels stay relatively low and I expect another 6-10″ snow around Mt. Hood above 3,000′. The snow level forecast based on the ECMWF model…

We get a break from the rain Tuesday, then another weak system moves inland Wednesday. That does give us a beautiful spring day Tuesday, but then it’s back to onshore flow and gloom Wednesday. Rain has been running below average this month, and we’re slowly making up a bit of ground. But it appears we’re headed back to drier weather again Thursday through next Sunday. See the upper-level ridging developing just offshore Thursday

Then it’s right over us next Saturday…could be well into the 60s with sunshine!

Then by NEXT Monday a cold trough drops in over us, crashing the warm/sunny party.

That should leave us with a bit of a dry spell. Most likely Thursday-Saturday, or possibly Thursday-Sunday. Or if we get leftover sprinkles Thursday, it would just be Friday-Sunday. The point is that you should be aiming for Friday/Saturday for guaranteed dry days. Thursday & Sunday will be bonus days if we can stay dry for those.

Hopefully no one missed the “big tornado” Friday evening? Portland NWS says a very weak EF-0 touched down very close to the Ilwaco airport. That’s near the mouth of the Columbia River NW of Astoria. 65 mph wind and damage could only be tracked for about 1/3 of a mile.

This is the latest in a series of very weak tornadoes in our area the past few years; all EF-0

On another subject, I spent almost two hours tonight “digitizing” a metro rainfall map.

Huh?

It goes back to Charlie Feris, a local Oregon AMS Member. Charlie worked at BPA as a meteorologist for many decades. During that time he set up a network of rain gauges around the Portland metro area. People would send in monthly rain totals and he would tabulate the numbers. I believe Charlie retired in the early 2000s but he has continued to “accumulate” the monthly rain readings. Over the years he has created a contoured map, showing annual average rainfall in our area. I remember first seeing this 20+ years ago. Then last March, at our last in-person AMS meeting, he passed out some copies. I told him I’d love to get it in graphical form so it’s saved for future use. That’s what I did this evening. Here’s the original version:

And (a very colorful) TV version…

Let’s talk about it. I don’t think many people are aware how much variation we get in annual rainfall here. A few points:

  1. In general it’s driest in the lowest elevations and wettest higher up. That makes sense because as clouds rise over terrain, they cool, moisture condenses, and raindrops form.
  2. There is a bit of a rain shadow coming off the Coast Range, possible off Chehalem Mtn. in southerly flow as well.
  3. The driest parts of the metro area are around Bethany and Tanasbourne areas westside, and Sauvie Island to I-205 bridge along the Columbia River. Some of these areas see less than 38″ in an average year. In fact the 30 year average at PDX is around 36-37″.
  4. Wettest (by far!) is the west slope of the Cascades. The eastern suburbs of Portland into the Cascade foothills pick up 50-60″ rain each year.
  5. Terrain has a huge influence not only on daily weather, but yearly precipitation.

Of course these numbers are averaged over a year. In certain patterns the variations on these maps can erased, or even enhanced. For example a strong westerly flow at 3-5,000′ can leave an inch of rain at Troutdale or Corbett, but almost nothing falls in Hillsboro. OR, a strong south-southeast flow in the first few thousand feet of the atmosphere can really soak the west metro (Banks, North Plains, Hillsboro), but leave those usually wet eastern suburbs significantly drier.

Alright, that’s it for now. Keep your fingers crossed for some warm sunshine at the end of the week.

Chief Meteorologist Mark Nelsen

24 Responses to Spring Break, A Tornado, & Wet/Dry Parts of Metro Area

  1. JERAT416 says:

    Pretty windy right now in Tigard, and I’m sure in other places too.

  2. Roland Derksen says:

    Windy, rainy day here tomorrow. It seems like every sunday we’ve had this year has the same weather! Can’t recall the last time we had a sunny Sunday.

    • Joshua Lake Oswego says:

      Shockingly, our rain for tomorrow is fizzling out. Looks like another .10” – .20” “event”. We might not get more than .25” in a day from Valentine’s Day to Halloween at this pace.

      • Anonymous says:

        You done complaining yet?

        • Joshua Lake Oswego says:

          Nope, not yet. But, since it’s so important to you, I offer the following… PDX gets .25’’ of rain in a day, I don’t complain for a week. .50’’ is good for two weeks.

    • Roland Derksen says:

      Actually, it looks like today’s weather systems has kind of weakened out here also: Clearing skies to the west, not a lot of rainfall fell, and winds may not become as strong as predicted. We’ll see.

  3. tim says:

    Possible wind event for w wa sunday and next friday according to nws seattle, a active start to spring this this year.

  4. W7ENK says:

    At my place, March now has the same number of overnight lows at or below freezing as February. That’s double the number in January, and one more than in both December and November.

    • boydo3 says:

      We’ve also had a chilly March here on the south coast but we’ve had 7.5″ if rain as well. So cooler temps but about average rainfall. In fact last week you could hike from sea level to snow level on Humbug Mt.

  5. Garron near Hillsboro airport says:

    Man, if that low of 14 verifies for Monday on your 7day forecast, that’s gonna be epic! I hope I’m seeing that right using my phone app.

  6. Roland Derksen says:

    Sunny but pretty breezy day here- feels quite chilly. I don’t know if that warmup for the end of the week will reach us up here in BC. It would be nice to get the temperature above 60F for the first time this year.

  7. Terry Finley says:

    Couple of questions….is the spring like weather this weekend brought to us courtesy of an East wind? And also, have we now abandoned the weather station at the Corbett school?! Ben offline now for a month. Thanks

  8. Joshua Lake Oswego says:

    Well, a pineapple express would be better than Mt. Hood erupting. I don’t see what your point is.

    • Anonymous says:

      The rest of us don’t know what your point is when you repeatedly complain there isn’t enough rain to meet your expectations.

  9. Joshua Lake Oswego says:

    The GFS (v16 as of today) gives us zero rain through April 7th after another underperforming event on Wednesday.

    Can we go two months in winter/spring without a single day over .25”? Very possibly. Today is day 37. We will barely avoid the driest March in history. That is for certain.

    • Anonymous says:

      Still better than a pineapple express that comes in and melts the snowpack. Also the Euro still wants a system to come through on Monday 03/29

    • Anonymous says:

      I believe what your stating in Lake Oswego. But up here in Castle Rock we have been really wet this month overall. We have had periods of dry weather but also periods of deluges. We have also been cold overall.

  10. lurkingsince’14 says:

    That low packed a pretty good punch last night as it came onshore 🌬 🌧

    Here’s to Thur/Sun🤞🏻 ☀️

  11. tim says:

    I think we all can agree were due for another 2015 summer records were ment to be broken the past two summers were fairly normal time to turn up the heat.

    • Jake in Gresham says:

      Uhhh, no thanks, climate change is going to make that more likely as we go into this new millennium but to say I want that as a local myself?

      I think you need to looking Arizona because the triple digits really are no fun with our long days of daylight relative to the South.

    • Anonymous says:

      No thanks, I’ll pass. Especially with increased fire danger. After being in a level 2 evacuation zone for days in September I’d happily welcome a more mild summer with no events – including heat waves.

    • Anonymous says:

      Nonsense

      2018 was HOT, it tied the record for number of 90 degree days. 2020 was also relatively hot, it had more than the average of 90 degree days. If anything, I would say we’re due for a 2019 year since that was also a La Nina year.

      You keep pushing this idea that mild or warmer weather in winter or spring spells very hot summers for some reason. Hard to tell if you’re just trolling with this one or actually believe it

  12. JohnD says:

    Thank you Mark—as always. All so fascinating and detailed. We weather geeks are very fortunate, indeed, to have access to your presentations. Thanks again.

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