First Cool Month Since March; Feels Like October!

September 16, 2018

9pm Sunday…

It’s been a very quick switch to not just early Autumn weather the past week, but it feels more like October with highs struggling to reach 70 some days.

Month Climate Temps Calendar

We’re running slightly below average for the month with no sign of warmer weather over the next 10 days.  That tells me we could actually end up with a cooler-than-average month.  That hasn’t happened since March.  And the rain is starting to (slowly) add up; we picked up another .35″ in the city today for a monthly total of 1.55″

Rainfall so far this month_compared to normal

That puts us above our typical September rain of 1.47″.

There were people worried in mid-summer that “Summer would continue into November” or it “would never rain again”.  Always keep in mind with weather that we have short-term memory.  The rain ALWAYS comes back.  And temperatures ALWAYS cool in the fall.  Even after the hottest summers we cool off.

We had a few heavy showers around the metro area earlier this afternoon but they are gone now.  I think we’ll be dry through Thursday, although a weak system might give us a sprinkle Wednesday night.  Otherwise our next wet system appears Friday.

It’s been much cooler this month due to an upper-level “dip” or trough in the jet stream.  You can see it’s still there on the GFS ensembles showing upper-level heights on Wednesday


The cool colors represent below average 500 millibar heights.  Then the same model for next Sunday shows the continuing cool pattern.


The ECMWF is similar and doesn’t show the upper-level trough dissipating until at least 10 days from now.  See the ECMWF ensembles showing the trough just starting to leave.


Very interesting since we were dominated by higher than average upper-level heights from late April through mid August.  I’ve always found it fascinating how a “switch can flip” and we go from one weather regime to another.  Typically it’s that late spring wet-to-dry switch.  But sometimes it goes the other way too and that appears to be the case for Autumn 2018.

Enjoy the 3-4 days of dry weather this week!

Chief Meteorologist Mark Nelsen

Fire Season 2018 Winds Down…A Lucky Year in NW Oregon & SW Washington

September 13, 2018

5pm Thursday…

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This has been a tough fire season again across the West.  Although some spots have been spared in our region.

In Oregon there have been two “hot spots”through the fire season.  That’s the numerous lightning-caused fires across SW Oregon that have burned for two months.  And then several very large fires (some from lightning, some human-caused) across north-central Oregon.

Assuming some huge new fire doesn’t break out in the next few weeks, (unlikely looking ahead weatherwise) I think we are well past the big danger period for this season.

Who got lucky in our area?

There were no major fires across most of NE Oregon, the northern Oregon Cascades, all of NW Oregon, and all of SW Washington.  As of this moment total acreage burned across the Pacific Northwest is significantly DOWN from last year as well…around 700,000 acres vs 1,100,000 or so last year.

Considering late spring and early summer was the driest or 2nd driest on record in our area I think we were very lucky.  It’s most likely due to lack of lightning.  For a second season it seems we had very little thunderstorm action both in the mountains and down here in the lowlands.  I don’t have the stats to back that up (yet), but I’ll find them eventually.

Fire Fuel Moisture Oregon2

The showers and cooler weather most of the time since late August has helped tremendously in the Cascades.  Check out the Log Creek “1000 hr fuel” moisture level this summer:  the black line is this year, yellow is last summer.   Blue is the average…you notice the woods in that area are typically driest in late August and then moisture increases in September.

Fire Fuel Moisture Oregon

This year we were running exceptionally dry through the third week of August, but then some showers brought us back up to average for that time of year.  Then you see showers the past few days have brought fuel moisture back ABOVE average for early September.  With more showers through the weekend and again later next week I have no reason to believe those fuels will dry out again.  Notice that huge dump of rain last September that put an end to the fire season.

To summarize:

  1. Much of Oregon remains dry, but cooler temperatures have lowered fire danger even in those spots
  2. Fire Season 2018 is winding down quickly west of and on the west slopes of the Cascades.  It’s not over yet, but the chance of large fires developing is going downhill.
  3. For the 2nd consecutive year fire season is ending a bit early; I doubt anyone is complaining!

As for weather…looking ahead I see a continuation of below-average temperatures through next week but Monday through Thursday should be dry.  Note the ECMWF ensemble high temperature forecast looks like early October


I love this graphic…the 24 hr accumulated precipitation product from the ECMWF ensembles.   You can glean lots of information quickly.  First the bottom section.  That’s the ensemble “average”.  You clearly see the best chance for significant rain is centered right on Sunday.  Looks like every single ensemble member (each is a horizontal line above) shows a tenth of an inch or more.  Maybe 20% give PDX more than 0.50″.  Then there is good agreement on a dry spell Monday through at least Wednesday and likely into Thursday as well.  We’ll dry out a bit.  But some decent hints also that late next week and the following weekend could be showery.  Good meteorological stuff!


Enjoy the mainly dry weather Friday, I think there will just be a few light showers popping up late in the day…many of us stay dry.

Chief Meteorologist Mark Nelsen

Wettest Day Since Early April In Portland

September 12, 2018

11pm Wednesday…

What a soaker for the central part of the metro area this evening!  Here’s the radar image from 6:20pm as thunderstorms were dumping huge amounts of water on inner NE and SE Portland.

KPTV 2017 Default Earth

Officially at PDX it’s the wettest day since April 7th and we also broke a record for the day

Rain Record PDX

Of course this time of year the record daily rainfall isn’t that hard to break…the old record was only 0.23″.  But wait, apparently even heavier rain fell between the official gauges.  There were several stations in inner east Portland that showed more than 1″ of rain; that would include the early morning rain too.

Rain Portland HYDRA Gauges.png

Tomorrow’s showers should be much more tame with most action over the Coast and Coast Range.

Chief Meteorologist Mark Nelsen


Downpours & Sunbreaks Tuesday Afternoon

September 11, 2018

3pm Tuesday

Thanks for all the helpful emails/tweets you’ve been sending about our website & app issues.  Since changing providers a few days ago, our IT/Web folks have been working hard to get things fixed.  Please be patient as they are trying to get all the links working again…Mark

There are lots of showers roaming around the region as expected this afternoon.  A cool and unstable airmass is overhead; dumping small areas of very heavy rain and leaving others with just a few sprinkles.

KPTV 2017 Default Earth

Here are the totals as of 3pm in the northern Willamette Valley & metro area


But in between those official stations some spots have been under a deluge at times. Tillamook and Yamhill counties have been very wet, along with Pacific and Cowlitz counties up in Washington

Rain Portland HYDRA Gauges

This showers & sunbreaks pattern continues Wednesday then the showers back off Thursday and Friday.  The bad news is that the weekend appears to be showery as well, especially Saturday.

If you have an outdoor event that can’t get wet Saturday?  Get a tent or find a covered area.  Sorry, but that happens sometimes in September.

Chief Meteorologist Mark Nelsen

Cool Showers Ahead & Low River Levels

September 9, 2018

9:45pm Sunday

Today was a spectacular late summer/early fall day with temps in the upper 70s in the metro area after starting out around 50.  We officially hit 80 here in Portland.  It COULD be the last 80 of the season, but I think it’s unlikely.  We can easily hit 80 in the last half of September and sometimes even early October (more rare).  I’m quite confident we won’t hit 80 in the next 6 days as we’re entering our coolest week since back in early June.

The well-advertised upper-level trough of low pressure that will sit over us most of the week is approaching.  That means a first band of showers tonight, then off/on showers Tuesday through at least Thursday…maybe into Friday as well.

Jet Stream Forecast 2017

As for rain, we could use a HUGE soaking.  At this point it appears we’ll get some decent showers both Tuesday and Wednesday.  Add a few light showers in Thursday and Friday and we COULD get up to 1/2″ rain in some lowland locations west of the Cascades.  Here’s the ECMWF forecast for the next week.  Not encouraging east of the Cascades but this will put Fire Season 2018 on life support west of the mountains.

ECMWF 7 Day Rain Total wGauge Mark

It’s hard to believe, but Salem is STILL breaking an all-time dry weather record. Today was the 90th day without rain down in the Cherry City

Dry Spells Salem

That should finally change this week; I think it’s unlikely you folks make it to 100 days.

Is this the beginning of a long wet period?  I don’t think so…at least at this point it seems that we back off the showers after Friday.  Note the 24 hour rainfall from the ECMWF ensembles shows most ensemble members turn drier after the 14th/15th.  Nothing like the dependable dry weather of summer but more of a typical September on/off again shower chances:


As for temperatures, you see the ECMWF ensemble temps hold us near or below normal most of the next two weeks


On another note, we ran a story here on FOX12 both last night and today about low water levels on the Columbia River are leaving some boats stranded.  This pic was taken Friday or Saturday by Katie Watts


I’ve been driving by/along the Columbia River on my daily commute for most of the past 25 years and see the level every day. Some years it goes REALLY low in September/October and other years it just goes a bit low (like this year).  But this time of year always features the lowest water of the year.  See the 365 day plot of river level at Vancouver shows it’s at the same level as last September/October and right around normal.


Looking at that you wouldn’t think there would be any boating issues…every early fall boaters need to watch for exposed sandbars.  But then take a look at the two week graph


A more interesting phenomenon shows up…the twice daily rise/fall of the river with the tide.  Even this far upstream the Columbia is affected by the ocean tides.  And I’ll admit it’s a greater range than I expected.  A 2-4 foot rise/fall every 6 hours appears to be the story this time of year.  On Sunday it fell over 4 feet in just 6 hours!  That means a boat you dock up against an island in 3 feet of water is suddenly stranded on dry ground the next morning.  Luckily the water WILL rise again…if you have 6-18 hours to wait…

Chief Meteorologist Mark Nelsen

Last 90 Degree Day Today? Big Changes Ahead

September 5, 2018

pm Wednesday

It was briefly hot out there this afternoon, with PDX reaching 90+ (91) for the 31st time this summer.

90 Degree Days Summer Heat

Easterly flow topped out between 20-35 mph at the west end of the Gorge this morning.  Pressure gradients turn back to light westerly on Thursday which should keep us below 90 degrees.

Was it the last 90 degree temperature in Portland this year?

It COULD be, especially considering we see no real warm/hot weather in the next 10 days.  That would take us to mid-September.  It’s interesting to note that in the past 6 years we haven’t reached 90 beyond September 20th.  The AVERAGE date for the last 90 is today…the 5th.  So there’s no reason this couldn’t be our last 90 of the season.

Mark Last 90 Degree Day Heatwave

It’s pretty obvious that we’re headed into a cooler pattern after Friday.   The warm upper-level ridge over us

Jet Stream Forecast 2017_1

gives way to a cool upper-level trough much of next week.

Jet Stream Forecast 2017_2

This means much cooler and cloudier weather is on the way; check out the ECMWF ensemble temperature forecast for the next two weeks in Portland.  Pretty good agreement with the operational model here.  Notice it shows coolest temps (relative to average for this time of year) appear to be early next week:


But the million dollar question…HOW MUCH RAIN?

If we’re going to be cool and cloudier, let’s get a good inch or two of rain.  But as of now that doesn’t look likely based on the GFS and ECMWF models

Both show at least 0.25″ in the lowlands, maybe even 0.50″ if we get lucky through next Thursday.  As expected they do hint at heavier rain in the Coast and Cascade Ranges.  Regardless, it’s obvious this will put a big dent in the fire season.  Even a little moisture this time of the year (with its low sun angle) can do a lot of good.  Check out an interesting fuel moisture graph that covers stations on the west side of Mt. Hood National Forest

RAWS_MtHoodWest A “1000 hour fuel” refers to large fuels (8″ diameter or larger).  First look at an “average” year…the gray line.  In the north Cascades of Oregon fuels in a “typical year” are driest just after mid-August and then gradually moisten up through September and October.  The red line is the driest the fuel has ever been (on any one date) through the period of record.The yellow line is last year; see how that dry east wind period around Labor Day kept fire danger extremely high until the 16th of September?  The Eagle Creek Fire blew up during this time and there were other huge fires burning across the Willamette/Umpqua National Forests.  You can see the season-ending rain event the following week as many inches of rain fell in the forest; a somewhat miraculous event for this time of year.  Also note the record minimum fuel moisture was set a few times last year, including much of early September.  This year we seem to have “bottomed-out” around the 20th of August, setting a few new “record dry” days just ahead of that time.  Showers and cool weather moistened things up the last week of August and earlier this week so right now we’re running just slightly drier than average for early September.  Hopefully it all makes sense, of course you can click on the image for a larger view.

To summarize:

  1. We have two more warm days and then we see a sustained period of cooler than average temps.
  2. Put anything away that can’t get rain on it Friday, or for sure Sunday
  3. If you have an above-ground pool like me, it’s likely it’ll be too cool to use after Friday.
  4. Fire Season 2018 should quiet way down next week, maybe not the end of the season but we will have passed beyond the threat for major fires.

Chief Meteorologist Mark Nelsen



Summer 2018: 2nd Hottest On Record In Portland

September 3, 2018

8pm Labor Day (Monday)

September has arrived and meteorological summer (June-August) has ended.  Sure, there will still be some very warm days and maybe even a 90 or two, but in general we’re done with the hot stuff.

Before summer began I think some of us were hoping it would just be an “average” summer after a series of hot summers.  That sure didn’t happen…it was a scorcher!


  • Weather was consistently warm to hot with few big swings toward extreme heat or cool.
  • But we didn’t break a single daily record high temperature in Portland!  Just one tie (95 on June 20th).  We only hit 100 once (July 15th), which is amazing considering it was the 2nd hottest summer on record.
  • Warm nights:  2 new record warm lows (June 12 & Aug 10) plus 3 tied record warm lows
  • Less morning cloud cover (marine air) than normal.  Seems like late July to mid August we hardly woke up to low clouds.
  • Summer “ended” somewhat abruptly after the 22nd of August.  Of course it didn’t really end but the heat suddenly disappeared.
  • Nelsen Pool Index: My above-ground pool peaked out at 85 degrees in late July and again during the hot spell in early August (same temp as last year).  But it has been very chilly and not really usable since that sudden change the last week of August.  Last year we were able to use it until the fire ashfall finished things off around September 4th.  Again, summer seems to have more abruptly “ended” this year.
  • We were dry, but nothing too unusual.  The very unusual part is the 1.5 month dry spell BEFORE SUMMER EVEN STARTED on June 1st!  That’s what has put us into a drought situation and is extremely stressful to vegetation/bushes/trees.
  • Where was the lightning?  I saw nighttime lightning once in late June  The next morning many of us woke up to a couple loud thunderstorms.  That was it!  What a boring summer, but that saved us from seeing lots more fire starts in the Cascades and possibly Coast Range.  We lucked out in the northern Oregon Cascades this year.

Here are the numbers,

MarkSummer WrapUp

Here’s how other cities around the region rank based on preliminary data:

Seattle:  2nd hottest
Olympia: 8th
Troutdale: 3rd
Salem:  4th
Roseburg: 6th
Medford: 8th
Astoria: 13th
Redmond: 6th
Pendleton: 24th

Note that for a bunch of these cities the top record-holding years are quite recent; we are living through a very warm period!  This has been the 5th consecutive warm/hot summer in the Portland metro area.

MarkSummer RecentYears

I can’t find a similar period within western Oregon in at least the past 100 years.  In the past there have always been cooler summers mixed in with the warm/hot summers, even during the warmer periods like late 1950s through mid 1960s.  Take a look at the past 100 years of Oregon climate zone #2, that includes most of the lowlands north of Eugene.  This is average summer temperature of all the weather stations combined, not including 2018.

download I’m not a climate scientist by any means of course.  But I wonder…

  1. Is the subtropical high that typically moves north in summer in the western USA wanting to build farther north lately, keeping us regularly warmer?  The western USA has warmed far more than east of the Rockies.  Many areas of the Midwest have seen little or no warming the past 100 years during summertime.
  2. If even without AGW (human-caused warming) we would have been in a warm period right now following that cool period around 2008-2011?  Basically is AGW piling extra heat on top of what was already a warm part of the climate cycle?
  3. If we don’t get much warmer the next 10 summers or so due to the Pacific ocean  remaining at almost the same temp.  There should be a limit to how much we can continue to warm with the same cold ocean sitting there giving us summertime marine pushes.
  4. Will we cool the next few years before heating up even more?  Or just stay the same before getting even hotter summers at some point in the future.

As for rain, of course it was dry, as it always is in summer.  But this year we saw less than 1/2 of our typical rainfall

Mark Summer Wrap Rain

It sure wasn’t a record dry June-August, but that follows an extremely dry 2nd half of spring.  The combo of May-August rainfall is the driest on record here.  We need a big soaking soon!

There you go…your Summer 2018 wrap up.  Hope you enjoyed the read and hopefully next year can be a bit more reasonable!

Chief Meteorologist Mark Nelsen