September Ends Cool; Some Mountain Snow Too

September 23, 2019

9:30pm Monday…

With a week to go, September is running near average temperature-wise.  That comes from a very warm start followed by the last 9 days of cool temps.  Across other parts of Oregon it’s a bit below average.


Looking ahead, it’s clear September will end very cool this weekend and early next week.  In fact it’ll be about the coolest it can get this time of year.

Right now the very weak late September jet stream is just to our north, sending plenty of clouds and a few sprinkles.  That general setup continues through Thursday.

Mark Jet Stream

There won’t be any weather systems nearby Wednesday so that should be a spectacular day like we saw this past Saturday.  But Friday through the weekend that strong ridge of high pressure offshore pushes west and north.  That forces a cold dip in the upper atmosphere south over the western USA.  This IS the same setup that sends cold arctic air down into the Pacific Northwest during the winter.

Mark Jet Stream3

But of course it’s late September so snow won’t fall down to sea-level, or anywhere close.

For the weather geeks, 850mb temperature is forecast by both ECMWF and GFS to fall to at least +1, and possibly as low as -2 over Portland/Salem.  The coldest on record over Salem anytime before October 7th is between -2 and -3.  So it doesn’t get much colder than this in late September.  What does that mean?  It means snow COULD fall as low as Government Camp (3,500′).  Of course that means precipitation has to show up.  The earliest fall snowfall at Government Camp was September 23rd, 1984 when 3″ fell.

ECMWF Snow Level From 850mb Temps LONG TERM

This setup is typically not a big rain/snow producer; because the air is coming down from dry land up north, not from the Pacific Ocean.  Take a look at three rain forecasts for Friday through next Monday.  Generally not much rain in the lowlands

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This general pattern is likely to stick around for awhile.  Both 6-10 day and 8-14 day outlooks from CPC show the same “western trough/eastern ridge” pattern continuing through the first week of October.


Mark CPC 6-14 Day Outlook wKML

Mark CPC 6-14 Day Outlook2 wKML

Chief Meteorologist Mark Nelsen

An Early & Wet Fall Continues; Even Cooler Temps On The Way

September 19, 2019

7pm Thursday…

It was dry today!  No rain in Portland today, what a nice break after so many downpours the past week.   Don’t get used to the dry weather, it’ll be wet again after midnight, plus Sunday should be a soaker too.  Maybe more important, all our models are showing even cooler conditions to wrap up the last 10 days of September.

Summer “ended” on September 6th this year in our area; that was the end of reliably  warm & dry weather.  There’s no sign of anything above 75 in the next week either and our very wet September will continue…

The updated September numbers so far for Portland.

Rain PDX Last 10 Days

A rain total above 3″ in September has only occurred a few times the past 30 years.  In 2013, 2010, & 1996.

Take a look at some other spots around the region, some hefty totals in the Coast and Cascade Ranges

Rain Totals Metro Area

The entire region has been wet too.  The precipitation anomaly for the past 10 days


What’s ahead?

Real quiet tonight through Saturday, but a strong onshore flow and a dying weather system gives us light showers tonight through the morning commute Friday.  Saturday still looks great, at least compared to what we’ve seen lately.  Partly cloudy with temps making it into the lower 70s; at least a little more reasonable for late September.

Sunday = a soaker as an upper-level trough moves overhead accompanied by a cold front.  The entire first part of the day should be wet, then it’s on to showers the 2nd half.   Monday should be reasonable as showers end, but cool with 850mb temps only around +5.  Even with some sunshine the best we’ll do is mid-upper 60s.

Weather geeks will recognize the weather pattern the rest of next week; a classic arctic blast setup for wintertime Wednesday through Saturday.   Look at the ECMWF ensemble 500 millibar height chart for next Tuesday.  A strong ridge attempting to build over and just west of the West Coast.  Heights go up to around 580 or so which is typically warm fall weather.  Yet there is plenty of fast westerly flow overhead which keeps us from getting very warm with lots of cloud cover and maybe even showers making it as far south as northern Oregon.


But see what happens by Thursday a week from now?  The ridge is retrograding (moving farther to the west) and building over Alaska.  That forces a cold airmass to move south through Western Canada.  You can see a cold upper-level trough dropping south around Juneau.  At this point it’s showery over us (although not stormy) and snow levels are heading down toward the Cascade Passes for the first time this fall season.


Then two days later…Saturday the 28th.  This is the pattern we had in February with cold (cool in September) Canadian air pouring south into the western USA.  A strong ridge is…wait for it…parked right over Alaska and the eastern Pacific.   Hmmm, just like February and parts of this past summer.  Interesting.  This pattern is not very wet and could give us partly cloudy skies with daytime highs in 60s and lows in the 40s.


I’ve only shown you the ECMWF ensemble maps, but the Canadian and GFS are very similar.  September will likely end cool.  The previous run of the ECMWF showed this similar “dipole” of a chilly western USA and warm east continuing into at least the first few days of October (through the next two weeks).  Surface temp anomaly from September 29th through October 6th…


The effect is clear; the 15 day ensemble low/high temps for Portland are almost all well below average for late September and early October



  • We are done with “summer weather” and even any significant warm & dry spells.  At least through the end of this month.  We can have spells of warm & dry weather in October, but that comes with nights in the 40s and highs in 70s; definitely not “summer-like”.
  • It won’t be quite as wet the next 7-10 days, but we could easily see another inch of rain or more in the next week
  • A first frost is likely many areas east of the Cascades within the next 10 days, and possibly a few of the coldest areas in Western Oregon and Southwest Washington.
  • Timberline Lodge at 6,000′ will likely see its first snow of the season about a week from now.  Snow may get down close to the Cascade Passes (briefly) too.

Chief Meteorologist Mark Nelsen

A Wet September, And More Rain On The Way

September 15, 2019

11:30pm Sunday…

A busy day with 5 shows this evening, but I’ve been watching lightning offshore from our Seaside and Lincoln City cams.  That’s been fun.

What a soaker today with around one inch of rain in parts of the metro area as a slow moving system moved overhead.  It was one of Portland’s wettest days this year.

In the first half of the month we’ve picked up our typical September rain AND it’s been the wettest first half of September in 23 years!

Rain Record PDX

There were quite a few spots that picked up more than 1″ of rain.

Rain Metro Today Databound.png

Cool and unstable air is moving over the very “warm” ocean water offshore this evening.  Did you know it’s 65-66 degree water just offshore?  That’s much warmer than normal.  These temps in Celsius of course.


The “Blob” covers a huge part of the Eastern Pacific this fall.  Just above all areas are running much warmer than average.  But that’s a story for another day…


So if you live at the coastline, expect thunderstorms at times tonight, but they should die as they move inland.  Then from midday tomorrow through afternoon, the inland heating with sunbreaks should give us thunderstorms with the associated downpours and possibly hail.  That will be for anywhere west of the Cascades including the Portland Metro Area.

Lots more rain to come with an organized frontal system Tuesday.  More on that tomorrow as we plow through a wet September.

Summer seems a long way back now…

Chief Meteorologist Mark Nelsen

Summer 2019 Wrap; A Surprisingly Warm Summer

September 11, 2019

7pm Wednesday…

It feels like autumn outside and there’s no sign of a long warm & dry spell ahead.  Fall is here which has worked out just about right this year.

Officially fall arrives weather-wise on September 1st according to NOAA & the National Weather Service.  Traditionally of course we think of it starting with the Autumnal Equinox late next week.  Regardless, as meteorologists we consider summer to be June-July-August so let’s take a look back at Summer 2019.   The numbers might surprise you.

First, let’s get this out of the way…


That includes both urban and rural areas.  Even now I’ve seen people claim this was a “cool summer” or a “terrible summer” on social media.  That’s a ridiculous claim and not supported by facts.


In many areas west of the Cascades, this summer was WARMER than any summer before 1958.  A better way to state this?  In the 1930s-50s this would have been considered one of the the warmest summers on record!  That shows how our summer climate has warmed over time.    First image includes lowlands west of the Cascades between the Coast Range and Cascades.  Second image is coastal areas.  Data from NCEI.




Even though west of the Cascades it was in the top 1/3 of “warm summers”, this summer was COOLER than the past six.  The coolest since 2012.  That also tells you how crazy hot the past few summers have been.  This is likely the reason many of you think it was a “cool summer”.  But definitely not.  In fact check out the 80 degree days in Portland; a bit above average so far

80 Degree Days Yearly


Warm nights were the rule this summer.  Of course in the urban areas it’s hard to chart long-term climate trends for low temps since cities turn warmer as they grow.  I covered that in a post earlier this summer.  But even in rural areas there were plenty of warm nights.  Part of it was due to cloud cover, some likely due to the return of a warm “blob” of water in the Eastern Pacific, and some due to a warm airmass in general.  Here are the PDX numbers, of course heavily influenced by the urban heat island

60 Degree Nights Portland


It SEEMS like we had more partly cloudy or cloudy days right?  Especially in early-mid July.  I think that may be where the feeling of a “slow start to summer” began.  That said, if we take all of June through August, we saw FEWER totally cloudy days than average.  And a normal number of clear days.   Anecdotally I would say that’s true.  Many of our marine pushes off the Pacific Ocean were weak this entire warm season.  Fewer thick morning cloud cover days but maybe more partly cloudy days in the afternoons?  Just a guess.

Mark Cloudy Days Summer


No heatwaves!  This was a strange one.  We had two very hot days in early June, then two more at the end of August.  Otherwise no extended periods of hot weather.  Many times from late June onward the models tried to push a hot upper-level ridge in over us.  But it only happened twice. It was continuously mild to warm but no long stretches of 90+ days.  In fact as of today we’ve seen just 11 days at/above 90 degrees.  That’s FAR less than recent years.  That’s also a little below the 13-14 day average.

90 Degree Days Summer Heat


Remember those dramatic predictions of “another smoky summer ahead” by some in media and elsewhere?  I remember thinking at the time that it all depends on what happens DURING the summer, not leading up to summer (a dry late spring).  Sure enough, we had occasional cooldowns and even some showers here and there to keep things in check.  It shows you how important the heatwaves are (plus lightning) in getting the big fires started and growing.  As of right now, this fire season is pretty much dead.  Fuel moisture on the western side of the Mt. Hood National Forecast is at a record high for this time of year too.  So far, less than 200,000 acres have burned in Oregon and Washington; the lowest number since at least 2010.  I have a feeling that isn’t going to change much over the next three weeks.

Fire NW Summer Stats

Chief Meteorologist Mark Nelsen

Weather Calms Down After Three Wet & Stormy Days

September 10, 2019

7pm Tuesday…

For the first time since Saturday we’re seeing a mellow evening in the metro area with respect to weather.  A chance for meteorologists to enjoy their dinner without a tornado warning showing up (twice).

It’s been a fun or crazy or annoying three days; depending on your viewpoint.

First, on Sunday we saw thunderstorms pop up quite late in the day.  One produced a tornado near Cornelius Pass, then as it passed through Vancouver a funnel cloud was seen by many;  but no touchdown in this case.  The NWS issued two separate tornado warnings for that storm

Tornado Today Stats

That tornado was the 2nd we’ve seen in our viewing area for 2019.  Remember the other was in NE Portland on July 1st.  Once again it was a very weak tornado.

Tornado How Many Each Category

The stats include all counties west of the Cascades from Centralia/Chehalis down to Lane county (Eugene).  Notice this tornado comes right during the autumn “tornado season” in our area.  Very loosely defined, but you get the idea.  There’s one other “season” in our area…May and June.  Still, twisters are rare in the Pacific Northwest.

Tornado Season Stats

That was Sunday, then yesterday lots more showers popped up in the afternoon.  There were two spots with unusually heavy downpours; east side of Hillsboro and Salmon Creek area in Clark County.  Check out these totals!  Most of these stations picked up all that rain within 2 hours (or less!).  I checked one home weather station near Westview High School: 1.88″ in one hour.  Amazing.

Rain Totals Metro Area.png

You might be wondering about the timing of the big downpours;  why not in the wet season?  It’s because warmer air can hold far more moisture than a chilly winter airmass.  So when it rains around here in the warm season it CAN really dump if the weather pattern is right.   In fact when I think of our big street flooding issues the past 20 years, typically it has been between May and October.

Today was day #3 with thunderstorms.  It did get quite intense during the early afternoon.  I see Lake Oswego picked up .80″ around 2pm.  As showers died down after 4pm in the metro area, the main lifting seemed to move south.  There were dozens of lightning strikes in the mid Willamette Valley.  Salem you had quite a storm during the evening commute.  In just a 30 minute period ending around 5pm, lightning detection picked up 44 cloud-ground strikes around Salem

KPTV 2017 Default Earth

The airport at Salem picked up .96″ in about 90 minutes.  Finally at 6:45pm I see most of the thunderstorms have dissipated.  It appears the official Portland observing location at the airport has avoided the big storms/downpours through these three days.  Still, we’re above average for rain this month.

Rain PDX Last 10 Days

A very brief look ahead says fall weather is here to stay.  There’s no sign of a significant warm & dry spell through at least the middle of NEXT week.  Here are the ECMWF ensemble hi/low temps for Portland the next two weeks (ignore the last day)


and ensemble rain forecast.  Good chance we get into the downpours/thunder action again this coming Sunday/Monday.  Maybe a bit drier around 20th or so, but then we’ll be deeper into the fall season.

ecmwf-KPDX-indiv_qpf_24-8116800 (1)

It’s quite possible that “summer ended” on September 6th this year.  We may not see any long stretches of upper 70s and 80s again.

High Temp Last 13 Days

By the way, a quick glimpse of Mt. Hood this evening shows snow stuck down to around 9,000′ on the mountain during our cool/wet spell

Cam Skibowl

Chief Meteorologist Mark Nelsen

That Tornado Warning in Portland Metro Area This Evening? UPDATED WITH 2ND WARNING

September 8, 2019

7:30pm Sunday…

Updated at 10pm Sunday…

Immediately after I published this post at 7:40 pm a 2nd tornado warning was issued for parts of Vancouver from the same strong cell.    Here’s a quick summary of the entire evening:

  • A heavy shower/thundershower moved from about Hillsboro to east Vancouver from 6:45 to 8:15pm
  • It prompted two separate tornado warnings (around Cornelius Pass and then central/east Vancouver)
  • It’s likely a tornado touched down around Cornelius Pass at a Pumpkin Patch (christened a “Gourd-Nado” by Brian MacMillan)

This pic from Jim Kessinger


  • As of this moment there are no reports a tornado actually touched down in Vancouver.  Apparently the “confirmed tornado on the ground” wording in the 2nd warning was because the funnel cloud appeared to just about touch the treetops.  So in reality a tornado was never observed on the ground, but very close.


Well that was exciting…for about 10 minutes.  If you have a weather app, or the FOX12 app, you probably noticed a TORNADO WARNING appeared for a small part of the metro area around 6:50pm this evening.  That’ll get your attention!

As far as we are aware, there wasn’t a tornado on the ground.  If it happened, it would have been right around Cornelius Pass & Skyline Road in extreme NW Multnomah County.

Here’s the sequence of events:

  1. Weather spotter (and local weather geek) sent pic and called in funnel cloud report.  It was seen north of Hillsboro Stadium over the West Hills.
  2. At the same time radar did indicate very weak rotation, although that alone typically wouldn’t lead to the Portland office of The National Weather Service issuing a tornado warning in my experience.
  3. So Portland NWS issued a tornado warning for about 13 minutes from 6:47pm-7pm.  Then the warning expired.
  4. No tornado was seen on the ground and no funnel cloud was seen over NW Portland as it moved off the West Hills and into the flatlands as far as I’m aware.

Radar looked like this when the warning was issued.  Nothing out of the ordinary


But checking out the Storm Relative Velocity shows there was some weak rotation almost right over Cornelius Pass at 6:45pm.  We get a real clear view since it’s only about 5 miles from the Dixie Mtn. radar site.

KPTV 2017 Default Earth

Green colors indicated movement TOWARD the radar site and red is movement AWAY from the radar.  So you’ve got some counter-clockwise rotation going on in that spot.  I’ve seen weaker rotation than this produce a weak tornado in our region.

Within a few minutes most of that “wind shear” or weak rotation disappeared.

That wraps up your funnel cloud story for this evening kids!  Here’s a pic of the funnel cloud from Mitch Etter, taken from Hwy 26 on the west side of the metro area

photo mitch etter

Chief Meteorologist Mark Nelsen

Summer 2019 Is Over; Should Feel Like Early October Next Three Days

September 7, 2019

7pm Saturday…

What a change today! A thick marine layer kept us cloudy & gloomy west of the Cascades and then a cold front has passed over the top of that marine layer.  Instead of the 81 we saw Friday, today we only hit 69 in Portland.  A nearly two week period of very warm weather ended today.

High Temp Last 13 Days


Taking a look at the weather maps today it’s obvious that “summer is over”.

What does that statement mean?

  1. The seemingly endless & dependable days of (mainly) dry weather and warm sunshine are finished for this season.  That’s perfectly normal for early-mid September.
  2. The chance of hitting 85-90 again is slim, but still possible
  3. The very warm nights we’ve seen much of this summer will soon be coming to an end.
  4. Expect at least 1″ rain for most of us in the lowlands by the time we get to Tuesday evening, with up to 3″ in some Cascade and Coast Range spots.  Fire Season 2019 will continue to limp along on life support; good news!
  5. Temperatures at pass elevations and Cascade mountain lakes go from 70s yesterday/today to 50s the next few days…that’s chilly camping!

What could we still see?

  1. A briefly hot afternoon.  We can hit 90 even in early October, although it’s rare
  2. Several nice periods of sunny & warm weather; remember those two weeks of sunshine the middle of last October?  Lows in the 40s and highs in 70s were wonderful.

By the way, officially summer ends August 31st according to NOAA; meteorologists consider summer the three month period June-August.  Traditionally of course summer ends at the equinox the third week of September.

The next three days will feature a cool upper-level trough moving over the Pacific Northwest.  This is a classic setup for showers, downpours, thunderstorms, and maybe a funnel cloud or two as well.  All models are showing an unstable atmosphere each of the next three afternoons as the “warm” air bubbles up into the colder airmass overhead.  Ready for some lightning numbers?  Here’s a neat chart showing lightning strike frequency in the metro area for each hour of the day and each week of the year.  You can see two maximums in frequency; late spring & early summer and again in September or very early October (now).  In this situation it’s rare to see it anytime other than afternoons/evenings.  I think it’s interesting that for fall lightning it has a quicker cutoff in the evening, likely due to much earlier sunset than May/June.


That upper-level low is right over us Tuesday on the ECMWF ensemble 500mb height chart:


Then east of here Thursday; that may be the best day of the week weatherwise.


Next weekend another upper-level low moves by, but may stay just far enough north to spare us a wet weekend; tough call at this point.


There are strong hints that we return to drier/warmer weather next week.  See the ridging over the western USA in 10 days?


As for rain, check out the ECMWF ensembles again for Salem.  Just about every member puts down 1″ of rain, with most of that in the next few days.


So hopefully everything you want to stay dry is now indoors or under cover.  Your yard/garden and our woods will get a much-needed soaking!  This growing season has been drier than average across the NW corner of Oregon and SW Washington.  The six month precipitation anomaly:


Chief Meteorologist Mark Nelsen