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  • Posted

9pm Friday...

December arrived with record warm temperatures across the region. Wednesday (the 1st) was the warmest December day we’ve seen in Portland since 2015! These are just a few of the records set that day. Notice several spots in eastern OR/WA set all-time December high temperature records.

Cliff Mass (UW) in his blog called this the 2nd great Northwest heatwave of 2021. By that he means that many areas east of the Cascades observed “heat” just as anomalous as the June event; 25 degrees or more above average in spots.

We cooled off nicely today after a cold front passed through yesterday morning. Highs today were back in the 40s along the I-5 corridor…much more seasonal.

What’s ahead?

The mild/warm westerly flow in the upper atmosphere is changing to a setup where cool troughs dig down from the northwest, passing through our region. Each one should spin up some sort of wet system. So we can expect precipitation regularly over the next 7-10 days. Here’s the view Saturday

Then Monday; another trough passing by

Then a third next Wednesday

Looking farther ahead, to Monday the 13th, models GENERALLY have more troughing digging into the eastern Pacific.

In general this whole setup the next 7-10 days is cooler than normal. At this point I don’t see any surge of cold arctic air moving south, but it may be close at times. This chart shows things well. It’s the ECMWF 850mb temperature ensemble chart. It shows temperature (C) around the 4,000′ elevation for the next two weeks. Green line is the average of all 51 ensemble members. I’ve drawn the yellow highlight at 0 degrees.

Basically for pass elevation snow in the Cascades it needs to be at/below that yellow line. That’s the case most of the next two weeks…very good. Finally, we’re going to see a snow base develop in the mountains, and it’s not going anywhere this time.

Lowland Snow?

It’s that time of year! The next 2.5 months are primetime for snowfall in the lower elevations of NW Oregon and SW Washington. I’ve got a few thoughts on that. The pattern I’ve shown above CAN bring snow to the lowest elevations of the region, but right now it doesn’t appear to be quite cold enough to do that. Sure, late next week 850mb temps dip to around -6 or even -7 at 850mb. That means foothill snowfall for sure (1,500′ or higher). But it takes more than that to get any sort of widespread snow event to the valley floors. I’m not saying we won’t see snowflakes at some point in the next 10 days, but nothing really sticks out on the maps right now. Note there is almost no support for significant snowfall from ECMWF ensemble members in the next 10 days. This is for Aurora/Canby; I chose a spot in the middle of the valley to avoid low resolution modeling issues. Ignore anything beyond 10 days…it’s a crapshoot after that.


  1. There’s no sign of a cold “arctic blast” the next 7-10 days. My exposed chicken coop waterline will remain on for now. Beyond that, the 15th and after? Who knows!
  2. I don’t see any sort of widespread snow/ice in the lowlands in the next 7-10 days. I haven’t put my snow tires on yet and don’t plan to for now. However, I would not be surprised to see flakes mixed in with rain at some point during that period. Or even a brief snow on the hilltops…maybe.
  3. It’s quite possible we see at least some partial ski area openings NEXT weekend, the 11th/12th

That’s it for now. Have a great weekend!

  • Posted

Sunday, Jan. 16th, 5:20 A.M.

Good morning!
Today is starting very similar to yesterday. We have morning fog and low clouds in areas, mainly in the western metro. Another dense fog advisory is in effect until noon today for the I-5 corridor. By noon we should see much of the fog clearing out and seeing much clearer skies. Along with sunshine, we'll see some partly cloudy skies this afternoon. By late evening clouds will increase slightly. Highs today will be in the mid to upper 40s.
Tomorrow we'll see another potentially foggy start and a partly cloudy afternoon. Late tomorrow night, a system will start to bring light showers to the region, continuing into Tuesday. Wednesday and Thursday wet systems will be moving to the north of us, but both days, it looks like showers could impact our region as well. Models are varying a bit on just how much of this wet weather will actually impact us, but it doesn't look like any day would experience heavy precipitation.
By Friday we will dry out again and return to partly cloudy skies. 
Temperatures remain above normal for the next 10 days. 

  • Posted

In the past week we’ve seen warmer than normal temperatures persist west of the Cascades, although no real hot days in the metro area. Lots of 80s, before & after the marine push last Wednesday/Thursday. Yet just one day at 90 degrees.

Meanwhile Salem has seen 8 days at/above 90 so far this month. Why? We are in a classic “northwesterly flow” regime. The setup has been very stable for over a week. Wind is coming in off the Pacific each afternoon/evening to replace hot air rising over the interior of the Pacific Northwest. The Columbia River gap allows lots of that cooler marine air to come up through Longview, Kalama, Clark County, and into the Portland metro area. This morning’s satellite image (8am) shows enough cool air and moisture for low clouds in a good chunk of this area. Clouds tend to form central & eastern metro first because the marine air is bottled up against the the western Gorge. This is why west metro tends to be sunnier more often summer mornings than the east side.

Farther south, in the Willamette Valley, no morning clouds = warmer. The layer of cool air is thinner there. Look at the effect on high temperatures today. 77 at Longview to 90 at Salem.

Strong westerly wind through the Gorge keeps Hood River comfortable, but by the time you get to The Dalles the airmass has warmed. Way out in Hermiston, today is the 25th day at/above 90 degrees. They haven’t seen a cooler than average day since June 16th!

There are 4-5 significant fires burning across Oregon this evening. This is an amazing visible satellite image considering it’s only July 12th. You can see a new fire south of Detroit Lake (Bruler), Grandview fire NE of Sisters, Jack fire NW of Diamond Lake, and the massive Bootleg fire north of Bly

That Bootleg fire exploded in size Saturday, becoming a “mega-fire”. That’s a fire over 100,000 acres in size. It didn’t change much through this morning, then you can see it has exploded again this evening. I estimate a 25-30 mile long “fire-front” based on GOES-17 fire detection

Oregon has seen 22 megafires since 1980, most of them in the eastern half of the state. Of course 5 of those just occurred over/on the slopes of the Cascades last September. You can find a recap of that event here:

What’s Ahead?

  1. Dry weather continues across the region through at least the next 10-15 days.
  2. A cooldown arrives Wednesday and spreads east of the Cascades Thursday-Saturday
  3. Then we warm up again early next week
  4. There’s no sign of a heat wave west of the Cascades through at least the 20th

Check out the 500mb anomaly map (from the GEM model) for right now. In general we’ve got higher than normal (warm colors) heights overhead

By Friday, a cool trough is sitting just offshore. But notice heights have only come down to around normal for this time of year. The hot ridge has weakened and moved back to the “Four Corners” region. This pattern gives us widespread morning clouds west of the Cascades. High temperatures drop back into the 70s…a refreshing mid-summer weather pattern.

But by Monday the hot ridge is back, just to our east.

It’s still there NEXT Thursday, the 22nd, 10 days from now. This says above normal temps, but not extreme. Especially west of the Cascades.

You can probably guess there’s very little chance for rain in this pattern. No organized weather systems come close to us. Look at a bone-dry ECMWF model forecast the next two weeks: Just a spot of drizzle out of low clouds. Not a single one of 51 ensemble members produces even a tenth of an inch through the 27th!

Let’s hope for very little lightning and no human-caused fires. 3/4 of last year’s fires in the Pacific Northwest were started by people.

Enjoy the rest of the week! Chief Meteorologist Mark Nelsen

  • Posted

11pm Friday…

I’ve been a bit busy on TV this evening…7 shows!


The next three days bring an extraordinary and unprecedented surge of heat not seen during recorded history west of the Cascades. That’s a dramatic statement, but I’m quite confident it’s going to happen.


Our forecast hasn’t changed much, with a few caveats:

1) We should PROBABLY raise Sunday and Monday’s 110 degree forecast to 112-114. That’s because just about all models are pushing us into the 110-115 degree range both days. For tonight I left it the same. But does it really matter at this point? There’s always tomorrow to up things a couple degrees

2) Models just about all agree that the thermal low (hottest air) will still be over us 3-5pm Monday. That’s why we’ve upped Monday’s high temperature forecast to 110. It’s possible Salem, Albany, & Eugene are down closer to 100 that day

3) Excellent agreement that a major marine push drops us around 15 degrees Tuesday…which means that day will be similar to today, around 95.

4) Easterly wind might just touch the far northern Oregon and southern Washington coastline during the daytime Sunday. The result could be spots that spike well into the 90s. Anywhere between Tillamook and Long Beach. An example…it’s possible that at 3pm Sunday it’s 80 at the Tillamook Bay jetty, 85 at Garibaldi, 90 in Tillamook, and 100 at the eastern edge of the valley up against the Coast Range. Just an example.

4) This is a dangerous heat wave for those without air conditioning; we have never experienced these conditions in our area. You will not be able to cool down apartments/homes Saturday and Sunday nights. As mentioned in #1, it’s possible Sunday afternoon features temperatures 110-115 with a dry easterly wind. Add in low relative humidity in the metro area and you get absolutely unreal and hellish conditions for our area.

The 3 Day Forecast is crazy…

And the 7 Day…

For comparison, the hottest temperatures on record in our area

All records in the valleys are 107-109. We’re going to exceed at least some of these numbers

Eastern Oregon in general is hotter in summer so records are higher. Note Oregon’s all-time high is Pendleton at 119 degrees. We used to think Prineville shared that record (119), but it’s unlikely that ever happened. Washington’s all-time high is 118 at Ice Harbor Dam just east of the Tri-Cities.

Some of these records could be broken. Maybe Bend, The Dalles, or La Grande. We will see!

I’ll be working through the weekend and into next week. Stay tuned and make sure you are following me on Facebook: @marknelsenweather and Twitter: @marknelsenKPTV. I will be updating those much more frequently than this blog. 

  • Posted

9 p.m. Wednesday…

This is it folks!…for days our weather models have been insisting we have a major heatwave on the way. In fact, for the past three days they’ve been forecasting never-before-seen numbers (hot) for parts of the region. Typically as we approach an extreme event (cold, snow, wind) models clue in a bit more and get more reasonable. But in this case they’ve looked almost the same for days. The extreme numbers aren’t going away. So we’ve gradually been upping our forecast high temperatures for the weekend as confidence grows. After some consultation with the rest of the weather team today, we’ve decided to go with an all-time record high in Portland this weekend. That would be HOTTER than 107 degrees. Here are the all-time records for some of the I-5 corridor cities and the year it happened. Notice they are all between 105-110. Downtown Portland records have the same 107 degree record as PDX.

First, for those of you not wanting to get into the meteorological details…


  • What could be the hottest heatwave on record in the Portland area (and much of northern OR/southern WA) arrives Friday and continues through Monday. At the very least, this will be one of the top 3 heatwaves in our area. Very warm temperatures, 85-95 degree temps, continue through the rest of next week.
  • Expect three 100+ days in Portland, and they may all be 105+
  • I’m very confident we’ll hit 106-107, and think 110 is quite possible for the first time here. Records go back to the late 1800s.
  • Humidity will be reasonable at first, but humidity will be up Sunday & Monday…it won’t be a totally dry heat like we tend to get late in the season (September).
  • Overnight lows may be the warmest on record in Portland too. Low-mid 70s Sunday and Monday mornings. That means homes/apartments will remain dangerously warm with no chance to cool off. Typically we see reasonable overnight temps in our area.
  • The only place to cool off will be the coastline…more like 75-85 out there over the weekend. Most likely you won’t be alone if you want to play on the beaches
  • I do not expect any sort of strong wind anywhere in the Northwest. Wind will be relatively light Saturday through Monday

The forecast could still change a bit, but all this is based on what we’re seeing just 2-3 days ahead of the event.


When I was 12, we suffered through the great August 1981 heatwave. I was living near Mt. Angel at the time. We spent a few days mainly down in the basement. Almost no one had air conditioning back then. Then when my career began in 1991, just out of college, I wondered when we might break that all-time 107 degree record in Portland. It was only a matter of time, but I didn’t think it would take another 30 years! I’m feeling pretty confident this evening that it’s finally going to happen.

A large and very strong upper-level ridge will begin developing just to our west tomorrow

Then by Saturday the heights really soar.

At this time, most models are forecasting 500mb heights over 597dm over southern British Columbia. Meteorologist Ryan Maue had a great tweet last night, mentioning that this would be an all-time record up over that area. And having a closed “dome of heat” just to our north keeps us in easterly flow from high in the atmosphere just about all the way down to the surface. You can see the WRF-GFS cross-section for Saturday afternoon through next Wednesday shows that easterly flow from Saturday through Monday afternoon.

850mb temperatures soar to +21 (C) Friday over Portland, +25 Saturday, and right around +30 both Sunday and Monday on operational ECWMF/GFS models. Ensemble averages from the ECWMF keep Sunday and Monday around +27 to +29. Anything above +28 is an all-time record for our area. The 850mb ensemble chart from the 12z Euro run shows the massive heat spike with the ridge. Very high confidence of +27 or above Sunday PM.

Down at the surface, a textbook perfect thermal trough develops Saturday. This is the WRF-GFS. Weak easterly flow through the Gorge, weak onshore flow right along the beaches. Almost no wind in the valleys. This, along with totally sunny skies, plus very dry air overhead, should lead to a very hot day.

Then Sunday…the thermal trough is right over the western valleys with a (10-20 mph) easterly wind through the Gorge.

At that point 850mb temps are somewhere between +27 and +30. THIS should be the all-time record hot day. Then on Monday things change a bit. A southerly surge of cool marine air is moving up the coastline and beginning to pour into the southern Willamette Valley. This COULD be a day where Eugene is 10 degrees cooler than Portland.

Onshore flow picks up that evening and we drop at least 10 degrees Tuesday. This is all pretty straightforward. But what has been shocking meteorologists is the surface temperature forecast from all the models. The ECMWF operational model looks like this. Crazy hot, exceeding Portland’s all time high by 7 degrees Monday afternoon! Most shocking to me is that the Euro generally has cooler surface temps than expected during warm spells. For example we’re going 97 on the day it’s forecasting 92. It’s hard to believe that would hold with those extreme temps Sunday/Monday, it’s not going to be HOTTER than 110 or 114.

Much better nowadays is to use ensemble forecasting…in this case 51 different members of this Euro model. This is just about what we are forecasting, accounting for the typically low Euro readings by adding a couple of degrees to most days over the next week.

Hopefully I’ve given you some reasoning for my “hottest forecast ever” here. Buckle up for a crazy hot weather ride!

I’ll be working right through the weekend and next week. So make sure you are following me on Facebook: @marknelsenweather and Twitter: @marknelsenKPTV. I will be updating those much more frequently than this blog. Most likely I’ll get a fresh posting done again Friday morning, if not tomorrow evening.

Chief Meteorologist Mark Nelsen

  • Posted

8pm Monday…

We hit 97 degrees in Portland today, the hottest day so far this summer.

Recall that we hit 95 back on June 1st. Today was our 4th 90 degree day of the year.

Weak (and hot) easterly (offshore) flow continued through this morning, but now onshore flow (westerly wind) has arrived west of the Cascades. Temps are cooling nicely compared to yesterday, especially near the Coast Range where the cooler marine air is pouring through the low elevation gaps. This means our “mini-heatwave” has ended; tomorrow will be much more comfortable. In fact the next three days should be nice, just a little on the warm side

Keep in mind our typical high temperature this time of year is in the 70s, so we’re only “cooling” down to 8-12 degrees above normal this week. That’s because the hot ridge is weakening only temporarily…Here’s the Thursday map

Already a new ridge is popping up just to our west. But watch what happens by Saturday

A massive hot dome of air directly over the Pacific Northwest. For the geeks, 500mb heights are forecast to 594dm or higher. The 18z Euro ensemble average even paints a 597dm just north of us.

This is major heatwave territory

The big meteorological questions with 5-6 days to go:

  • How strong will the ridge be and where exactly will it be centered?
  • How high will 850mb temps go? Operational model runs are forecasting hottest ever recorded over Salem on Sunday (+30 to +31 on both GFS/ECMWF). Could that really happen? It’s never been above 28.3 there.
  • Will there be offshore flow…or weak onshore flow? That the difference between 102 and 108 (just an example)
  • How long will the hot ridge stick around?

For now, our 7 Day Forecast looks like this. Those numbers Saturday-Monday are a bit on the low side considering what we’re seeing on models:

I’ll get into more detail tomorrow as hopefully things become a bit more clear. For now…

  1. We have a heatwave coming next weekendIt’s TBD whether it’s a “typical” heatwave or something historic.
  2. Make your plans based on that information. If you don’t have AC…maybe head to the coast or Cascades?
  3. IF power goes out next weekend at your home, and you have a medical condition, what would you do? Start thinking about that.
  4. The all-time June temperature record (102) is in jeopardy at PDX
  5. This entire 2nd half of June is going to go into the history books as a scorcher, like 2015. Keep in mind today was the 6th day with a high temperature at/above 80 in Portland. There will be at least 7-8 more.

Chief Meteorologist Mark Nelsen