Unusually Warm and Sunny Start to October

September 27, 2020

8pm Sunday…

Now that we’ve seen a nice soaking across most of the region, it’s time for some classic early fall weather. Cool nights and mornings plus briefly (very warm) afternoons. Fall in the Pacific Northwest is typically like this; rainy periods alternate with bright sunshine. The key messages…

  1. It’ll be all dry through at least next Saturday/Sunday
  2. Temperatures reach 80 degrees or warmer Monday through Friday
  3. A gusty east wind blowing out of the Gorge will arrive in the metro area tomorrow, then come and go through Friday.
  4. Fire smoke is unlikely to return in any significant fashion in the lowlands. But high-level smoke from California likely arrives Wednesday. Expect much hazier conditions Wednesday-Friday

Today was about as normal as it gets…we hit 51 last night and 75 today in the city. 1 and 3 degrees above the 30 year average. Strong high pressure is now in place overhead. Here’s the view for Tuesday…

The typical fall jet stream is diverted far to the north and then plunges south into the Great Lakes region. We go much above normal and they turn very chilly. It still looks similar NEXT Sunday, October 4th, although the ridge has “flattened” a bit. That could lead to onshore flow and areas of fog/clouds. We’ll see how that plays out.

Regardless, rain is not in the cards through at least next Sunday. Actually the GFS model ensembles (newly upgraded last week!) show the ridge popping up a bit again early-mid NEXT week. Here’s Wednesday the 7th (click for a better view). Warm colors indicate a positive (warm) upper-level height anomaly.

The ECMWF and Canadian models look the same. So confidence is relatively high that we have a dry (or mainly dry) 8-10 days ahead.

How warm? 850mb temps over Salem sit between 20-23 for the next six afternoons! This would be a major heat wave in summertime. But this time of year a “heat wave” is 80-90 degrees. We appear to have good offshore flow the next two days, then it backs off a bit Wednesday. A bit stronger again Thursday, weakening Friday. At no time do we have a strong east wind event. More of a typical “gusts 40-55 mph in the Gorge and breezes over the mountains” setup. That begins tomorrow. I’m going with these numbers…only Tuesday and Wednesday would be close to record highs.

If you don’t like warm/hot weather, at least this time of year long nights mean we’re back in the 60s soon after sunset. Lots of 40s/50s for overnight lows of course.

I just check past Portland weather stats to see how uncommon 5 days in the 80s is this time of year. Not unheard of, but somewhat unusual. So how many days have we made it to 80 AFTER this date? This will be the most since 2014-2015.

But you have to go all the way back to my first year in TV…1993 to find another early fall with this many 80 degree days. Definitely unusual. In 1987 we saw 8 days at/above 80 this late in the season, and 1991 was similar.

Everyone keeps asking me about smoke…will it come back? I think that’s a yes/no question.

  1. Little or no smoke was visible on the perfectly clear GOES-17 satellite image today. There’s no reason to believe any of our local fires will suddenly start raging out of control or even put up a big plume of smoke again. That’s due to wet forest, no strong wind forecast, and some good fire lines.
  2. But, communities close to those fires may be smelling smoke regularly again or we could even get a slight haze down here in the lowlands. That should be about it.
  3. MORE NOTICEABLE…As the upper-level high shifts slightly east of us late Tuesday, a southerly flow opens up overhead. This means Wednesday-Friday could see a lot of milky/hazy sky overhead with filtered sunshine. Hopefully that wouldn’t make it all the way down to the surface.

Here’s the GEOS-5 modelling that shows smoke about to arrive Tuesday evening. You can see the center of the upper-level high around La Pine at that time.

By the way, check out this 20 year span of Portland metro area PM2.5 pollution. Except for last year, our late summers have turned smokier; you aren’t crazy in thinking that’s the case. The poor air quality you regularly see in late fall and early winter is due to inversions; common due to weak sun angle and long nights. Data is from EPA

A Much Needed Soaking Continues Through Friday

September 23, 2020

9pm Wednesday…

Now that was a soaker during the evening commute. A strong Pacific frontal system moved onshore the 2nd half of today, bringing gusty wind to the coastline and heavy rain to many areas.

Peak wind gusts along the coast were generally 40-55mph in the cities. The usual highly exposed spots saw gusts over 70 mph. A 76 mph gust at Cape Foulweather and 75 mph at Barview Jetty just west of Garibaldi are the highest I’ve seen. Those southerly winds died down after the cold front passed. But just this hour a westerly wind gust of 69 mph was reported at a temporary IRAWS weather station on the Lionshead Fire southeast of Breitenbush Lake. Luckily it’s raining with high humidity and temps in the 40s too!

During the evening commute a few areas saw buckets of rain. Aurora airport picked up 0.52″ between 5-6pm. Troutdale saw .39″ at the same time. Here are metro totals as of 8pm

The 0.68″ in Portland so far today makes it the wettest day since mid-March! That’s only as of 8:30pm. It’s quite possible we go above the .74″ on March 14th and see our wettest day since late January. Spring was relatively dry. Similar to Friday’s thunderstorms, some spots have been a bit wetter today…

What’s Ahead?

  1. Expect two more wet days, then just a few sprinkles/showers Saturday
  2. A long dry spell begins Sunday
  3. September ends and October begins warm, sunny, & dry

Tonight’s cold front was the first of three organized system moving through the Pacific Northwest. The 2nd arrives Friday morning, then a very weak ripple in the jet stream comes through here late Friday night and Saturday morning. The upper-level pattern shows a cool trough offshore that will rotate by to our north the next two days; (click for a better view)

How much MORE rain can we expect? Quite a bit for late September. Here’s one model’s forecast…shows maybe another 0.50″ or so in the valleys and 2″ additional in the mountains. This is excellent for the leftover smoldering Riverside and Beachie Creek fires; there won’t be much left of them. East side of the Lionshead fire will not get as much rain so it’ll keep limping along.

By Saturday a weak upper-level ridge has begun to show up, but it’s slower to get its act together and that’s why we’ve kept a few showers in that forecast

But check out Monday! Huge and hot upper-level ridging returns over the West Coast. 500mb heights up above 594dm! One month ago we’d be going for mid-upper 90s. BUT, it’s the end of September and unlikely we’d hit 90 in this setup.

By Thursday October 1st, it is STILL there. This is the ECMWF ensemble average…the average of 51 ensemble members. West Coast ridging and cold fall weather across eastern USA.

The brand new GFS ensembles (should do better this winter) look the same for next Thursday, although slightly weaker

The main message is that we’re headed into an unusually warm and dry period for all of next week, starting Sunday. The extended WRF-GFS cross-section shows a (more typical) east wind episode begins Tuesday. I’ve circled the wind forecast up around 2,000-4,000’…dry and warm

At this point I’m not too concerned about another widespread fire episode since Cascade forests will have been doused with 2-5″ of rain over the previous 10 days. It’ll be early October too…long nights and inversions in the valleys = less time for a fire to burn actively each day.

Alright, that’s it for tonight. Enjoy the rain the next few days; you look forward to some beautiful blue skies and warm temperatures next week.

Chief Meteorologist Mark Nelsen

Thunderstorms Deliver; And Smoke is Gone!

September 18, 2020

7pm Friday…

It’s been an exciting 24 hours!

Thunderstorms showed up as expected last night, most of them west of I-5 until early morning. Then 2-5am a large cluster of storms moved from near Lebanon up into the metro area. I wasn’t watching closely, in fact I was asleep Midnight-9am except for an hour around 4am. That’s because way out on the eastside I only saw lots of flashing, some occasional distant rumbling, and a sad 0.20″ total rain! That’s okay since the May 30th event was spectacular way out here. For the central metro area down to Salem it was an epic nocturnal lightning event; and well predicted by models! It was nice to see both summertime events west of the Cascades forecast well.

Some of you witnessed the heaviest rain of your life! Or at least the heaviest in a few years. Some spots saw more than 1″ in an hour, or even 30 minutes. That’s serious tropical moisture. Check out the official totals:

As always with thunderstorms we’ve seen a HUGE variation in rainfall depending on location. Ignore Kelso, something is wrong with that rain gauge. The massive downpours missed some of the official stations. For example, when that cluster of storms started moving north around 1:30am, it just nailed the Stayton/Sublimity areas. Here’s an account from Denny, about 6 miles east of Sublimity… “Last night between 1:30am and 2am I had 1.6″ of rain (mostly in 20 minutes) and 2+ inches of 3/4″ hail with continuous lighting causing a mudslide from a tree farm across the road into my driveway and pasture. Two foot deep in places, what a mess…” This is a pic he sent us, notice all the hail still lying around at least 6 hours later.

Just looking at totals over 1.00″… mid Willamette Valley (click for a better view)

Then the metro area…just totals at 1.00″ or higher

And late this afternoon/evening some flooding rain up in Kelso/Longview area. Lots of flooding on streets and hearing that first floor of hospital was at least partially flooded.

Clearly this marks our turn to fall weather; the long summer dry spell that began around June 20th has ended. The long period of “dependable dry” is over. We ended up with less than 1.50″ rain in the past three months. Looking ahead, I see a few showers tomorrow and then again around Wednesday PM or Thursday next week. There’s no sign of a long dry spell ahead; time to start paying attention to the rain forecast again.

And how about that smoke??? It’s gone! A southwesterly push of clean marine air came into the metro area between 3-4pm; suddenly the air quality went from poor to excellent. Even the Gorge has cleared out. The only spots left with bad air are in Central Oregon. Our 8 day “smoke storm” has ended. It was 10-11 days from Salem south since you folks had 2-3 days of smoke from the Cascade fires while Portland metro area stayed relatively clear. Current readings from www.purpleair.com

All those beautiful green circles…Portland is at 18! That’s even better than most summer days. Another site I use is http://aqicn.org/city/usa/oregon/portland/ In general we stay with good air quality from here on out, that’s unless wind direction turns south or southeasterly again. That would bring smoke north from California, SW Oregon, or Cascade wildfires. But our own fires in the Cascades will be knocked down a bit due to cool weather, high humidity, and some rain from this point forward. Not out, but more of a “creeping fire” instead of torching quickly across the landscape.

That’s it for now, enjoy your smoke and “weather-free” weekend. I’ll be back at work Sunday afternoon and take a look ahead into the last week or so of September. October is right around the corner…

Chief Meteorologist Mark Nelsen

Thunderstorms Tonight Help Clear Out Some Of The Smoke

September 17, 2020

4pm Thursday…

I’ve been off work the last three days and will be through Saturday. But I want to update you on two important changes ahead. Tonight looks especially interesting.

First, I see almost nothing has changed with regard to smoke. We are in an unprecedented (at least for the past 40 years or so) smoke event over the region. This is the 8th consecutive day with VERY UNHEALTHY to HAZARDOUS air quality in the Portland metro area. I never saw that growing up here and sure haven’t in my career that started in 1991. We’ve been receiving a “double-whammy” of: light wind at sea level keeping surface conditions smoky, plus tons of high level smoke streaming north from Oregon and California. They have conspired to keep temperatures well below what they should be in the current weather pattern. The effect is that this fire/smoke event brought our “summer to an end” on the 10th this year, when under normal circumstances it would have continued through today. We don’t have any sort of spell of “summer weather” in sight. Fall is here weather-wise starting tomorrow.

My wife is tired of me saying “if it wasn’t for the smoke we’d be sunny and in the low 80s again today”. That would be the case today of course. If we didn’t have fires burning, this could have been a record warm first half of September. But you see starting a week ago the dense smoke kept us a solid 10-20 degrees cooler than we would have been otherwise.

Air quality numbers at 3pm:

Yesterday evening was interesting down in the south Willamette Valley. That’s because a weak westerly push of marine air briefly dropped Eugene and Albany down into the GOOD to MODERATE category. But then a light northerly wind today has allowed the pollution to slosh back into the southern valley.


This is the biggie. We haven’t seen this setup since the end of May; a nice nocturnal lightning event is on the way.

  • Anytime after 8pm then on through sunrise tomorrow, ANY of us west of and in the Cascades (including coastline) could see quite a light show.
  • In fact the Portland NWS has the recently burned areas under a Flash Flood Watch since any heavy rain on dry/burned soil will cause all sorts of trouble. Landslides, rock fall, trees drop, etc…

The Storm Prediction Center even has us under a MARGINAL to SLIGHT risk of severe thunderstorms. A severe thunderstorm in this case would be a damaging wind gust over 58mph or large hail. Yes, that could happen during the night. Rare, but I have seen it happen here. And no, no one knows why SPC still uses those categories. Does any normal person know the difference between MARGINAL, SLIGHT, & ENHANCED??? No.

What’s the reason? It’s the large upper-level low offshore that’s been spinning in circles all week. Tonight it makes the big move. Right now, notice the southerly flow in the atmosphere. Imagine how many fires are upwind this afternoon, thus the continuing dense smoke overcast:

Then tomorrow midday, it’s about to move right over Portland…

By Saturday midday it has moved to the east, and we have a west-northwest flow overhead. By this point all upper-level air will be coming in clean off the eastern Pacific!

There is a lot of moisture as this system moves in. HRRR says about 1.50″ precipitable water west of the Cascades…that’s juicy!

The way the low is moving in leads to tremendous lifting in the atmosphere the next 12 hours. Especially 8pm-2am. This IS the classic setup for thunderstorms west of the Cascades. Each model is slightly different with location and timing, but I think the NAM-NEST represents reality well. At 8pm storms are starting to pop just to our south.

But by 1am they are spreading north quickly

And by 6am it’s obvious SOME of us will have seen downpours, others relatively light rain

It’s important to not focus on specific spots; the point is that over and west of the Cascades we’ll see some heavy rain from thunderstorms during the overnight hours. Some areas could see up to an inch of rain, others just a brief wetting.

Beyond sunrise tomorrow, we’ll be into a more typical spring/fall showers & sunbreaks pattern. That continues the rest of Friday.


  1. A westerly breeze and thunderstorms should clear out the densest fire smoke by sunrise and we’ll just have a smoky smell/view instead of this hazardous stuff. That’s an improvement.
  2. Then much cooler air overhead with the upper-level low will finally break the inversion we’ve been under for 8 days; that should help quite a bit. Lots of the surface smoke should easily mix out after sunrise.
  3. Continuing westerly flow in the upper atmosphere starting late tomorrow through next week should keep California and Oregon fire smoke moving east and away from us.


Enjoy the weather “show” tonight and hopefully we avoid any significant flooding issues in those burned areas. This will be our first measurable rain in about a month; which means roads will be slick at first too. Stay safe!

Chief Meteorologist Mark Nelsen

Smoke Lingering as Inversion Won’t Go Away

September 14, 2020

Noon Monday…

A very brief post to let you know…it still looks like this outside. View from Dayton at our Stoller Family Estate Cam

Air quality is still terrible at all inland locations at midday. Keep in mind any number above 300 is considered HAZARDOUS. There has been a slight improvement in just a few spots (Tualatin Valley & Longview) compared to yesterday.



  1. The dense smoke layer is not part of the input for weather forecast models. Those models don’t know we’re staying chilly in the lowest elevations compared to how “we should be”. Typically we’d be in the lower 80s today under this weather pattern. In fact many areas way up in the mountains will be in 70s. But we’ve been stuck in the low-mid 60s; smoke is blocking a significant amount of solar radiation.
  2. Smoke modeling is BASED OFF THOSE NOW INACCURATE WEATHER FORECAST MODELS. For example the HRRR smoke modeling showed a surge of cleaner westerly wind coming inland last night. That was assuming we warmed up inland yesterday, that would give us the typical onshore flow in the evening. It didn’t happen and the smoke remained.
  3. These same weather forecast models keep trying to bring in a general southwesterly breeze this afternoon across the whole area. That would help “ventilate” some of the low level smoke up into the atmosphere. We have better conditions several thousand feet up with a breezy southwest wind. It’s just not happening down at ground level. But I have doubts that will really happen. Pressure gradients at 11am sure don’t show it’s about to happen.

I’ll be on the air for a bunch of this evening’s shows…starting at 4pm.

Cliff Mass has a much better write up about the current situation on his blog this morning. He’s a professor up at the UW, who I consider the “Godfather of PACNW Weather”. Actually he was my favorite when I was at UW back in 1991. I highly recommend reading his post today.

Chief Meteorologist Mark Nelsen

When Will The Smoke Go Away? Saturday Evening Fire Update

September 12, 2020

10pm Saturday…

These are sure strange days…dense fire smoke is covering most of the western USA right now, especially along the West Coast. Take a look at the afternoon image from GOES-WEST. Click on any of these images for a better view

The smoke has moved so far offshore that it’s wrapped up into an upper-level low. A closer view shows smoke covers almost all of Oregon and Washington. I’ve circled a large plume pushing above the smoke layer over the Lionshead Fire, just east of Olallie Lake in the Cascades. Another plume is over the Brattain Fire just south of Paisley.

Of course we all know what it looks like down in the smoke layer. A sickly and cool yellow/orange world.

THIS IS THE WORST AIR QUALITY FOR THE LONGEST PERIOD OF TIME I’VE SEEN IN OUR AREA. This is our third day in the very unhealthy to hazardous category. Look at the numbers, most of us in the HAZARDOUS level. I’ve rarely seen a city go above 300; but Portland is around 500! The problem is not only smoke coming from those fires, but a weak push of cooler marine air has put us in a strong inversion. Temperatures in the 60s in the lowlands but 70s higher up. If we didn’t have the smoke we would have been in the lower 80s today.

When will it improve? Maybe slightly better tomorrow afternoon, but I think Monday should be much better with a strong push of westerly wind. Look at the HRRR smoke modeling for midday Sunday, this is a bit better than today

Then midday Monday…MUCH better

Smoke will still come and go next week since a system offshore will keep sending smoke out of California, but hopefully this long episode of dangerous smoke will end Monday

What about the fires? More good news today. No significant growth towards Molalla, Colton, Estacada, Silverton etc… in the past 2.5 days. Once the east wind disappeared the fires really slowed down. 700+ square miles burned with the 3 north Cascade fires. Today more of the area around Olallie Lake was burning as well as Trout Lake on the Warm Springs Reservation. It appears the Lionshead joined the (now in mop-up phase) P515 fire today too. So there is a 60 mile long corridor from Lyons to west of Warm Springs that has burned. That’s amazing.

Farther south, the Holiday Farm fire and Archie Creek fire continue to burn

Those fires will all burn until heavy rain and/or snow flies later in the fall.

To summarize:

  1. Fire fighting conditions continue to be good through the foreseeable future. No sign of hot/dry easterly wind for at least the next week
  2. All the Cascade foothill towns that are in Level 3 or partially burned shouldn’t see any additional burning. Hopefully lots of you get to go home in the next few days!
  3. Dense smoke should turn into more reasonable smoke in the lower elevations after tomorrow.
  4. The big fires in the Cascades will be burning for quite awhile. Luckily we’re not far from October when wetting rains usually end the fire threat

Chief Meteorologist Mark Nelsen

Quick Thursday Evening Fire Weather Update

September 10, 2020

10pm Thursday…

It’s been another extremely busy day for fire crews over and west of the Cascades. These last two days have seen an unprecedented number of large fires west of the Cascade crest.

There is one bit of bad news, but much more good than bad weatherwise this evening.

First, evacuation zones have been expanded in Clackamas County; Level 3 (GO NOW) includes Marquam, Estacada, Colton, & Molalla. Even Oregon City, Canby, & Sandy are in a Level 2 (BE READY) zone now. You can find this map on the Clackamas County page Click for a better view…


ABSOLUTELY NOT AT THIS TIME! Authorities are being very careful and proactive. They are making sure people are not in danger in these towns. An “abundance of caution” might be the best phrasing here.

But there is very good news for evacuees weatherwise…the dry east wind is gone! The most dangerous “explosive fire growth” phase of this event has ended. As a state official said at a news conference earlier today, he felt today was the day “we’re turning the corner”. That’s good news.

At this moment wind is either calm or almost calm everywhere west of the Cascades. I can’t find a wind gust over 15 mph inland from the coastline! That includes the Cascade foothills as well. And that wind is coming from a westerly direction = more moisture from the Pacific Ocean. A fire sure won’t be racing westward out of the mountains and down into the lowlands in these conditions. Check out relative humidity, way up from the teens and 20s yesterday at this time in the valleys.

The two coastal fires are now under the influence of a chilly & humid marine airmass. They are done making any advance towards the beach towns (Lincoln City).

Where do we head from here? A brief summary…

We now enter a more “normal” forest fire situation in the mountains and foothills. Each afternoon through Sunday a westerly breeze develops, but this will push those fires mainly eastward, farther into the mountains. So if a town hasn’t burned yet, it seems very unlikely it will from this point forward. But fires WILL continue to grow; these are massive fires!

To summarize…in the lowlands of Northwest Oregon.

  1. There’s no reason to believe any of the large fires will suddenly advance farther down into lower elevations (westward) and into more towns/cities.
  2. Thick smoke will be with us through Saturday, possibly Sunday as well. Air quality is hazardous in much of the metro area right now, and down into the Willamette Valley.

Now that things are settling down a bit we can take a look at the acreage…the numbers are stunning. Here are the “mega fires” burning in and along the west slopes of the Cascades. Click for a closer view on each one

The 900 square miles of public/private forestland burned hits relatively close to home. I grew up in this area and know how important timber is for these towns. My wife grew up in Sweet Home with relatives in Mill City, Gates, & Blue River. Remember that private timberlands support families and communities too, not just national forests. For some people their future income just burned up, along with a home and/or town.

That’s it for now. I’ll be on tonight at 10/11pm and the evening shows again tomorrow.

Chief Meteorologist Mark Nelsen