Heat Wave Update: Monday Evening

July 31, 2017

9pm Monday

Today was the beginning of our heat wave, but at least it was just a “regular” hot day.  Temperatures moved into the lower 90s in the Willamette Valley:

Todays Observed Highs OrWa 2017

Forecast-wise nothing has changed the past 24 hours.  In fact our 7 Day forecast looks just the same as it did 24 hours ago for the next 3 days.

7 Day Forecast Graphic 2017

One change is temperatures remaining near/above 90 degrees through the weekend.  Models are much slower weakening the upper-level ridge hanging along the coastline this week.  As a result the cooler marine air will only slowly leak into the western valleys of Oregon and Washington.  This means we are in a stretch of as many as 8 days at/above 90.

Hot Headlines2

Here is our current forecast vs. records for each of the next 3 days.  The record highs for the first few days of August are pretty low hanging fruit as they say.  Easy records to break!

Mark Hot 3 Day PDX Forecast

By the way, here is a list of Portland’s 5 hottest days, notice we’ll have to get to 106 to make it into that list.

Mark PDX Record Hottest Days Ever 100.png

So hang on, we’re in for a hot ride tomorrow.  Models are in good agreement giving us 5-9 degrees of warming, which should put us into the upper 90s by 5-6pm.

One other note; there is quite a bit of smoke to our south and north plus northeast from fires in the region.


At this moment I don’t expect enough smoke over NW Oregon to have an effect on high temperatures.  But even just a thin veil of smoke any of the next 3 days COULD be enough to keep temperatures 1-2 degrees lower than forecast.  We’ll be watching that closely.

Chief Meteorologist Mark Nelsen

Historic Heat Wave Begins Monday

July 30, 2017

7pm Sunday

The first few days of August will feature the hottest temperatures we’ve seen in at least 8 years west of the Cascades.  Just two years ago we had our longest heat wave on record here in Portland, but we didn’t hit 100 degrees.  This time the heat sure won’t last as long but it’s going to be hotter.

I’ve been forecasting in Portland for 26 years (and lived here most of 48), so I’ve seen lots of heat waves.  The forecast numbers from the models for this coming week, specifically Wednesday and Thursday, are right up with or even higher than anything I’ve seen!


PLEASE check in on your older friends the next few days, the heat is especially hard on elderly folks if they don’t have air-conditioning.

I expect 6 days of 90+ weather beginning Monday.  We’ve done that 12 times in Portland weather history.  It’s unusual, but not an extreme event.

We’ll get at least two, possibly up to 4, 100+ days.  I see Tuesday-Friday (4 days) having the possibility of reaching 100 degrees in the western valleys of Oregon and extreme SW Washington (including the metro area).  I’m VERY confident we’ll go way over 100 both Wednesday and Thursday, with Friday being the best bet for a 3rd 100 degree day.  Tuesday we might be a degree or two shy of triple digits.  It’s quite rare to get more than 3 days at/above 100 as you can see from the stats, we haven’t done that since 1981.


Overnight lows will be “reasonable” for this kind of heat.  We’re lucky that relative humidity will be near normal through the week and we won’t see any cloud cover.  That allows temperatures to cool down into the 60s for most of us.  During the 2015 heat wave humid weather and occasional cloud cover kept us very warm.

The all-time record of 107 degrees in Portland could be threatened either Wednesday, or more likely Thursday.  All through my career I’ve watched other cities reach new all-time highs (Seattle, Reno, Olympia) and wondered when PDX would finally hit 108.  It’s not like any of us WANT it to hit 108, but it’s a numbers game I suppose.  I have forecast 105 & 107 for Wednesday/Thursday here in Portland.  But to hit 107/108 everything would have to just right (or just wrong…right?).  During the 2009 heat wave we thought it might happen but there was a little too much easterly wind and that may have stolen a degree or two.

The Oregon Coast will have some hot weather too, but not as extreme.  Right now I’m thinking 80s Tuesday & Thursday, with a few lower 90s possible Wednesday only.


Why so hot?  A strong ridge of high pressure (a hot blob of air) develops right ON the West Coast this week.  You may recall earlier in the summer that hot ridge was to our east, over Utah.  Now it’ll be right over the top of us.  For the geeks, it appears to be a 594-595 decameter high center.  That strength of a ridge isn’t unusual at all centered farther to the east, but it’s almost right on top of us for this week.

This is the 3rd day models are showing 850mb temps (the temperature in celsius around 5,000′) in the +27 to +28 range Wednesday and Thursday afternoons.  They also did that during the July 2006 heat wave and we remained below 105 degrees.  When we get this extreme, forecasting an exact high is…a bit inexact sometimes.  Anything over +26 is quite rare.  In fact we’ve only hit +27 (over Salem on the balloon sounding) a few times in the past.  The all-time record is +28.3 on September 2nd, 1988.  We hit 105 that day, which was just amazing for early September!  We now have the possibility of seeing that during the hottest part of the summer with a higher sun angle.  If that +28 actually shows up, it’ll be unprecedented for early August, thus my forecast of 107 Thursday.  Note the excellent agreement among the ECMWF model and its ensembles through Thursday:


Also note the temperatures stay above average after our heat wave ends next weekend. It’s a bit of an understatement to say that at least the first 10 days of August will be warm!

As for records, just by chance the first 3 days of August have never been above 100 at the airport weather station.  That means it’ll be easy to beat those records:

Mark Hot 3 Day PDX Forecast

The National Weather Service is forecasting a high (114) warmer than anything in the past 25 years down in the Rogue Valley.  Wednesday (circled numbers are records for either day or all-time) forecast highs:


With more records to come around the region on Thursday:


I’ll keep you updated this week on the blog, but remember you can follow me on Facebook and follow on Twitter for more frequent updates.  You see those feeds on the right side >>>> over there >>>

Chief Meteorologist Mark Nelsen





Vacation Time

July 19, 2017

I will be on vacation most of the next 2 week, heading both north into Canada and south to Diamond Lake.  It’s the best weather of the year so time to get outside and the weather looks quite slow as well.   No posts until at least Sunday the 30th.

Another Perfect Day

July 17, 2017

11pm Monday

For many of us this summer season has been just perfect.  Pete Ferryman even mentioned it’s the best summer he can remember recently.  I think there are 3 reasons for that.

  1. NOT MANY GRAY MORNINGS  We have seen very few gloomy marine layer days in the past month.
  2. COOL NIGHTTIME TEMPS  Wow, what a change from the last 5-6 summers!  This morning was another chilly one with lows down into the 40s in many parts of the metro area. Homes cool off quickly in the evening and air-conditioning is hardly needed.
  3. LACK OF EXTREMES In past 11 days…every single day has been between the lower 70s and mid 80s.  No showery 67 degree days, but no 90+ days either.

Look at the lows last night…as cold as 40 out in Colton, but low-mid 50s in the city

PDX Observed Low Today

This continues our summer theme; a real lack of “very warm” nights.  I doubt many of us are complaining

60 Degree Nights Portland

Those numbers are up through July 18th…remember how unbearable Summer 2015 was?  For sleeping this summer has been the best since 2011.  Little or no air-conditioning needed!

And of course our daytime highs have been quite reasonable since that brief hot spell back in late June

High Temp Last 13 Days

But what I’ve really noticed is the sunshine.  It seems like almost every morning I’ve been waking up to sunshine (or at least partly cloudy skies) since the 3rd week of June.  I don’t care if highs only make it into the low-mid 70s; a sunny start to a day really raises my mood!

I expect more of the same for the next week or two.  Other than a brief passage of a disturbance this Thursday, I don’t see a setup for rain showers.  Even then, the chance of getting measurable rain Thursday is looking quite low.

Chief Meteorologist Mark Nelsen


Eclipse Weather: Hopefully Better Than Today!

July 13, 2017

11pm Thursday

There will be tremendous pressure on meteorologists in August to produce a sunny forecast on a certain day about 5 weeks from now.  Will it be sunny across the Pacific Northwest at 10am on Monday August 21st?  Of course that’s the date/time for the big solar eclipse.

We don’t know about the weather or cloud cover this far ahead of time of course;  we won’t start seeing glimpses of what might happen until at least 7-10 days ahead of time.

But we CAN go back in time and see what has happened historically.    Take a look at NOAA’s work on historical cloud cover over the region on that date:

Eclipse Cloud Climatology 3

The best place to be based on past weather is east of the Cascades.  The worst is along the coastline.

The WORST CASE SCENARIO for the eclipse would be a wet upper-level low sitting over the Pacific Northwest giving almost all of us mostly cloudy or cloudy skies.   The BEST CASE SCENARIO would be tomorrow’s weather…a thin marine layer that gives mostly or all sunny skies to the entire region, including the coastline.  Neither scenario is very likely.  More likely is some sort of cloud cover SOMEWHERE west of the Cascade crest.  Look at what happened today with a thick marine layer!  9am satellite pic:

Satellite GOES16 Vis Only

If the eclipse was today, almost no one west of the Cascades below 4,000′ would have seen it!  But everyone in the Cascades and east of the mountains would have had a cloud-free view.

It all depends on what kind of weather pattern we are in, but again, the best chance for clear sky is over and east of the Cascades.  I’ll be stationed both Sunday night and Monday morning/midday in Madras doing live reports on FOX12.

Keep your fingers crossed!

Chief Meteorologist Mark Nelsen

The Perfect Weather Pattern? July So Far

July 10, 2017

10pm Monday

The weather is extremely slow this week once again as we continue under an unusually stable summertime weather pattern.  Let’s be honest, it’s pretty boring in the weather center.  That’s fine though, summer is time for hiking, camping, bicycling, and all sorts of water sports.  Time for some vacation days!

Today is our 24th consecutive dry day in Portland; not unusual, but as mentioned in previous posts it started a bit earlier than normal.  In fact the rainfall anomaly (percent above/below average) for the past 2 months shows spring ended and summer started drier than normal; quite a turnaround from winter and early spring.


Temperatures have been running about 2 degrees above normal here in Portland, but anywhere east of the Cascades it has been a scorching hot first 1/3rd of July:

4 of the past 5 years we’ve seen these above normal temps in early July.

There is no sign that we’ll see a return to either cool and showery weather (unusual in mid to late July) or extreme heat in the next 10 days.  Take a look at the 500 millibar (18,000′) height anomaly for this coming Saturday.  It shows the western ridge strengthening once again, but far enough to our east to avoid a heat wave west of the Cascades:


Looking ahead to NEXT Wednesday, the 19th?  The ridge weakens a bit, but upper-level heights are right around normal.  Normal above = average tempratures down here where we all live.

Then out to Day 10…

The ridge might try to strengthen a bit again…maybe some warming.  But nothing extreme heat-wise.  Keep in mind this is from the ECMWF ensembles, which is a collection of many different runs as opposed to looking at just one run of the model.  Note the GEFS ensembles (from the somewhat inferior American equivalent GFS model)

show little or no rain in the next two weeks, which seems reasonable in the pattern shown by the Euro model above.  I think most of us would say we deserve this unusually stable summer weather pattern after the winter of nearly constant rain, freezing rain & snow.  So get out and enjoy what nature is providing you this Summer of 2017!

Chief Meteorologist Mark Nelsen

Happy Independence Day!

July 3, 2017

10pm Monday

The weather looks excellent for our nation’s big holiday!  A little on the warm side in the afternoon, then just right for fireworks

Independence Day Fireworks Forecast

I’ll be doing some emceeing out at the Corbett Fun 4th Festival after 5pm…look for the bright flag shirt!  Plus the only fireworks show east of I-205 in Multnomah County.  Let me tell you, conditions will be FAR better than 6 months ago in the same location!

Weaker onshore flow the next 3 days means warming temperatures as we stay in the “sweet spot” between a blazing hot upper-level ridge centered over Utah and a cool upper-level trough way offshore.

Jet Stream Forecast 2017

We will see just enough of nature’s air conditioning west of the Cascades (ocean air) to keep our high temperatures at or below 90 degrees…no heat wave for us.  But for you folks east of the Cascades?  This will be the hottest period so far this summer.

Looking farther ahead, we’re heading through our 3rd dry week with no rain in sight.  Relatively high heights (upper-level ridging) holds through the next 1-2 weeks.  So our stable summer weather pattern will continue as long as the strong ridge is sitting just to our east.  Notice the lack of rain on the European model ensemble forecasts for Salem.  Each horizontal line is one member.  Green says .10″ rain accumulation.  Only 2 of 51 members generate .10″ = most likely it’ll be dry or mainly dry for the next 2 weeks.


June just finished of course and it appears we’ve broken the string of 5 cool & wet months (December-April).  Both May and June were warmer than normal across most of the West, including Oregon.  Here’s the temperature anomaly for the past 60 days:


Precipitation has turned around dramatically since the very wet winter and 1st half of spring.


Only coastal Oregon and parts of Western Washington were around average, it’s been drier across the rest of our viewing area and Oregon.

That warm & dry pattern continues through early July…stay cool and keep watering your plants/lawns/trees!

Chief Meteorologist Mark Nelsen