A 100 Degree Day For Some, More Ahead

August 18, 2016

9:30pm Thursday…

What a scorcher today!  Even without east wind showing up much yet in the western Gorge (at least more than a light breeze) we saw high temperatures poke into the low 100s in parts of the northern Willamette Valley.

Here in Portland we officially made it to 99 at PDX, breaking the record of 96 set just last year on this date…


Check out the 100 Degree Club!


Even Astoria briefly got in on the act…a day early, with an 88 degree high.  That gives you an idea of what is possible tomorrow with a downslope easterly wind out there.  Forks, Washington made it to 96 as the easterlies arrived mid-afternoon.

Tonight rising pressure east of the Cascades means the east wind kicks in through the Gorge and maybe a little over the Cascades as well.  That means we will totally mix down the dry and hot air mass overhead.  I haven’t changed our forecast this evening since everything still appears on track for another record-breaking day tomorrow.  But there are a few minor tweaks…


  • Two more days of record-breaking hot weather ahead.
  • Areas AWAY from the Gorge will likely see another 1-3 degree rise in high temperatures.  That means high temps could be up around 104 degrees in a few spots like Hillsboro, Salem, or Battle Ground.
  • Areas that get the gusty east wind NEAR and IN the Gorge will actually be slightly cooler.  Troutdale likely stays below 100 degrees Friday.
  • The official high temperature forecast at PDX is problematic because too much wind could keep it below 100 again, or if the wind stays light enough it could be 104!  We went in the middle and have a 102 degree forecast.
  • Exact numbers don’t matter because it’s going to be baking hot tomorrow and the heat will begin earlier in the day.  Today it was 81 at noon in Portland. Tomorrow it’ll be 85-90 in those windy locations already at noon.


For the weather geeks out there, the 850mb temperature ended up just as forecast this afternoon over Salem.  It was 24.2 degrees.  The atmosphere overhead will be about the same tomorrow, but offshore flow really kicks in, thus the thoughts above in the highlights.

Looking further ahead, we DO get some quick cooling Sunday with a major marine push.  That should drop us a good 15 degrees, then another 5-10 degrees cooling Monday.  Much better!

That said, it appears there will be one more warmup the 2nd half of NEXT week.  This time temperatures will remain below 95 degrees, hopefully only up around 90.  No rain in sight!

Chief Meteorologist Mark Nelsen





The Big Heat Wave Begins

August 18, 2016

9:30am Thursday…

Hunker down (or find a cool river/lake to enjoy), it’s going to get really hot!  The NWS has a plethora of excessive heat warnings, advisories, and red flag warnings for most areas WEST of the Cascades from this afternoon through Saturday.


  • High temperatures the next 3 afternoons will be somewhere between 98-104 degrees in the lowlands of western Oregon and SW Washington.
  • We have never seen 3 consecutive 100 degree days (or even two) after the 15th of August, so if we get two or three that will be unprecedented.  That said, we’ve been quite close a few times in the past.
  • Breezy north wind today turns to a gusty easterly wind coming down off the Cascades and through the Gorge Friday.  That wind continues through Saturday morning, then it goes just about calm (hot!) Saturday afternoon.
  • Much more reasonable Sunday with highs at best around 90 degrees as a strong marine push begins
  • At the Oregon Coast, today will be much warmer with a few 80s possibly showing up, but FRIDAY is the scorcher with east wind pushing high temps well into the 90s for many towns.


Everything is on track this morning for a very late season heat wave.  Once we get past mid-August it’s very rare to hit 100 degrees.

A hot atmosphere has developed overhead.  850mb temps during the balloon sounding over Salem showed a +21.8 degrees, just what models have been forecasting.  They also say it’ll peak out around +24  to +25 for the next 3 afternoons with the trusty ECMWF forecasting those numbers.  That’s crazy hot, especially for 3 consecutive days with offshore flow.  I think the all-time highest August temp at 850mb is +27 during the 1977 heat wave.  It hit 105 in Portland that day.  So I’m pretty confident that we’ll get at least one day above 100 and we might possibly do all 3.  This is what we’re forecasting right now for highs at PDX and the records we should break:


Friday or Saturday will likely be hottest since 1) Friday has the best offshore flow and we start “pre-warmed” from today, but not so crazy windy that it holds the temp down a few degrees AT Portland airport and, 2) Saturday we start with offshore flow and then the wind goes calm in the afternoon, yet we don’t start to get a cooling northwest wind up the Columbia River.  Those are just about perfect heating conditions for PDX.

Offshore flow has already begun this morning, even at the surface there is a very light easterly gradient through the Gorge.  In the Cascades an easterly wind has begun with gusts to 30 mph at Three Corner Rock north of Bonneville and 30-40 mph gusts at the top of Upper Bowl Chair at Skibowl.

I expect temps to slowly rise through noon, then really take off.  During a heat wave in 2008 the temperature rose from 82 to 102 from noon to 5pm, proving that the warm air above can surface quickly!

As mentioned earlier, hitting 100 this late in the season is tough to do…in fact the last time we got above 100 in the 2nd half of August (or early September) was way back on September 2nd, 1988!  I remember shoveling corn and carrot slop on that day working at National Frozen Foods in Chehalis (my job for 6 summers in high school and college) inside the plant.  Geez it was hot!  Obviously no air conditioning in a place like that.  There’s nothing like warm carrot “goo” at 100 degrees.  Yet, it did allow me to get out of college almost debt free!


Stay cool…

Chief Meteorologist Mark Nelsen


Heat Wave Update: Hottest of Summer & 90s at Coast

August 16, 2016

9pm Tuesday…

It’s gonna get hot!  Okay, that’s a bit of a cliché but it’s true, I see a real scorcher coming up the 2nd half of the week.


  • Thursday-Saturday highs will be somewhere between 95-103 in the Willamette Valley and Portland Metro area.  That’ll be the hottest 3 day stretch of summer
  • Strong east wind arrives Friday not only in the Gorge but also west slopes of the Cascades and down into the valleys.  That means extreme fire danger and maybe some downed corn stalks too!
  • Fire danger will be extremely high west of the Cascades Friday and Saturday with the dry east wind.  Any fire that starts could spread very quickly.  Historically the largest fires west of the Cascades have spread in just these conditions here in western Oregon.
  • Friday may be the warmest (hottest) day in almost two years at the Oregon Coast.  For one day (Friday) and possibly part of Saturday, east wind will make it to the Oregon Coast.  Assuming that occurs, high temperatures will be in the 90s (yes, 90s!) in many spots out there.

Things have changed a bit in the last 36 hours.  First, a hot upper-level ridge is going to develop just to our west Thursday-Saturday, in the offshore waters of the Pacific Northwest.  No change there, but now models show a small but potent disturbance dropping down the east side of the ridge, bringing a taste of fall into Montana.  The next question is “what does that have to do with us?”.  That cool air is high pressure, so now all models are in agreement we get a strong easterly flow over the Cascades and through the Gorge.   Here’s the Friday 5am surface pressure map from the ECMWF.  The yellow line is the lowest pressure, air will flow toward that “thermal trough” as we call it.  Notice it’s on or even off the coastline at that time = east wind all the way to the beaches.


That easterly flow is the “icing on the cake” for a “perfect” heat wave.  850mb (5,000′) temperatures are forecast to remain near +22 to +24 (celsius) from Thursday through Sunday morning.  Such hot temperatures would typically push us well up into the 90s or even about 100 degrees this time of year.  Add in the extra heating as the dry wind races downhill off the Cascades and you can add another 3-5 degrees.  As a result there is no reason we can’t get to 100 degrees or above at some point between Thursday/Friday/Saturday.


On Thursday the offshore flow is just getting going in the afternoon, so I kept the high temperature down to “only” 98 degrees.  It’s sure possible we hit 100 degrees though.  Friday is the trickier forecast because we may have so much east wind blow here in the metro area that it might keep our high temperature “down” a few degrees.  As a result I’ve gone with a 95 for PDX.

Saturday (at this point) looks like the hottest day to me; hot airmass in place, easterly wind to start then it goes mainly calm in the afternoon, and full sunshine.  I put a 100 for Portland that day due to those factors.  Sunday we lose the offshore flow so even though it’ll be hot it should be well below 100 degrees.

Hitting 100 past August 15th is tough to do in Portland due to decreasing sun angle and about 2 hours less daylight than late June.  But check out 3 past episodes including Portland high temps and 850mb temp measured over Salem.  Notice how the atmosphere was overhead in 1977!

August 16th/17th 1977

102 deg / 850mb temp +24.6
105 deg / 850mb temp +27.0

August 14/15th 2008

102 / +24.6
100 / +26.6

August 18th/19th 2015

96 / +23.4
97 / 20.6

The coast is always a very tough forecast during hot weather episodes but this is what I’m thinking right now:


Saturday is the tough forecast day as we get a flow reversal and its southwesterly surge of fog and cool air pushing up the coast.  Friday will likely be the hottest day we’ve seen at most locations along the Coast since September 2014.  That month we saw a day with high temperatures in the low-mid 90s out there!

This whole episode is a bit extreme, but definitely not something “unprecedented” or unheard of in mid-August.  It just doesn’t happen that often.  In fact there have only been 5 days in Portland’s history where the temperature has made it to 100 degrees from the 18th of August through early September.  Interesting that 4 of those happened in 1986, 87, & 88 isn’t it?

Chief Meteorologist Mark Nelsen


Heat Wave #2 Later This Week

August 14, 2016

11pm Sunday…

It has been a hot and sometimes sweaty 4 days!   Check out the PDX numbers:



At McMinnville, Troutdale, and pretty much all of the Willamette Valley it has been 4 days at/above 90.  Whew…time for a cooldown.  Sure enough, we are finally getting drier air/lower dewpoints along with a weak marine push this evening.  That should drop the valley temperatures a good 8-10 degrees tomorrow keeping high temperatures below 90.

The bad news is that we have another heat wave on the way later this week.  This one is a little different because it’s brought on by a bit more of a “fall pattern”.  A cool shot of air drops into Montana; that’s high pressure to our east Thursday and Friday.  Then we get easterly wind over the Cascades and through the Gorge.  Not a strong wind like mid-fall but enough to push our temperatures way up.  Right now it looks to me that we’ll see high temps in the 95-100 degree range both Thursday/Friday.

So much for a “cool” summer (which wasn’t cool anyway); it appears August is going to end up very warm.  As of now we’ve seen 8 days at/above 90 in Portland, and we have at least 3-4 more.


Chief Meteorologist Mark Nelsen


Warmest Stretch Of Summer Ahead

August 10, 2016

6pm Wednesday…

This summer has sure been different.  A perception I keep hearing is that it’s been a “cool and cloudy summer”.  The cloudy part might be partly right, but it definitely has not been cool here in Western Oregon and Washington.  June was above normal and July was near or 1-2 degrees below normal:

I think what sticks out this year is a lack of very hot days; and I don’t think any of us are complaining!  That said, it IS a bit strange to go from early June to early August and only see 2 days above 90 degrees.  Note the 5 warmest days so far:


How does this summer compare to the well-known “green tomato” summers?  Not even close.

July average high temperatures at PDX and rain:

1954   72.6  1.24″
1955   72.2    .89″
1983   75.2  2.68″
1993   72.8  2.41″
2011   76.9    .96″  <– Not really a green tomato year but close
2016   79.1    .66″  <– Rainfall exactly normal

Yeah, this past July was definitely not “wet” or “cool” west of the Cascades…just NORMAL.  And it’s obvious why 1983 and 1993 stick in our minds…cool and very wet!  I wasn’t around for 1954-55 but those must have felt about the same.

Where do we go from here?  Models say we’re headed for the longest/warmest period of the summer between now and the third week of August.

Check out the 850mb ensemble chart from the ECMWF.  The thick line is the average temperature this time of year over Salem (in celsius).  Note that just about all of the next two weeks the forecast temps are ABOVE that line:


There is a huge amount of spread after about day #8, but most of those 51 ensemble members are above average.  The actual forecast highs for Portland look like this:


That’s the most consistent warm to hot weather we’ve seen so far this summer.  And considering we’re moving through mid-August, that’s likely to end up the warmest as well.  Once we get to late August temperatures typically are cooling off a bit.

The GEFS ensembles are similar:


so confidence is high that a prolonged spell of warm to hot weather is on the way.  No rain in sight either of course.

By the way, the all-time high temperature at PDX was set on this date 35 years ago.  During the big 1981 heatwave we hit 107 not once but twice!  That was a huge scorcher.  As I recall I was 12 years old and watching a Planet of the Apes marathon right here on Portland TV from the cool family room in the basement.  It may have been on KPTV as well!  Full circle right?


We’ve actually hit that 107 mark THREE times…one day in July 1965 as well.

Chief Meteorologist Mark Nelsen



Cool Next Few Days, Then Warmer, Then Cooler

August 5, 2016

11pm Friday…

Quite a bit cooler out there this evening, I see it’s already down to 60 here at the FOX12 Studios.  A major marine push means some low clouds Saturday morning, but I think we’ll see tons of midday/afternoon sunshine.

Sunday through Tuesday a weak upper-level low drifts across Washington giving us June-like (or is it September-like?) weather for a few days.  Due to this we might see showers on the coast Sunday, especially up north:


Enjoy the cooler weather because the heat is on again late next week.  There is good model agreement on a warm-up Wednesday-Friday next week.  Ensemble model numbers from both GFS and ECMWF show 90 is likely again in P-Town for a day or two.  There is pretty good agreement not only on the warm-up but a rapid cooldown again around the 15th.  Check out the GFS ensembles…this shows temperature at around 5,000′ over Portland for the next 16 days:


Quite a roller-coaster look isn’t it?  At least no one can complain that we’ve been stuck in just one pattern this summer!  The ECMWF ensembles are similar, so my 12 Day Trend graphic looked like this tonight:


I use this most nights at 10:45pm to give a general look beyond the 7 Day forecast.

Enjoy your weekend!

Chief Meteorologist Mark Nelsen

Warmest Day of the Week

August 4, 2016

9am Thursday…

Today looks like a hot one.  I think most of the metro area will end up between 88-92 degrees.  For the first time in a few weeks we have very light EASTERLY flow over the Cascades and through the Gorge; that’s when air is flowing from land toward the sea.  I see the pressure gradient is about 0.5 millibar from Portland to The Dalles.  You can see the (light) easterly flow on the Troutdale profiler nicely this morning.


Current time is on the left side of the image, 48 hours back in time is on the right side.  Two things show up; note the easterly flow from about 1,200′ up to at least 5,000′.  But what really sticks out is the dramatic warming overhead since yesterday morning.  At 3,000′ yesterday it was around 50 degrees at 7am.  Yet at 7am today it was in the low-mid 60s at the same elevation.  Combine that with the offshore flow and we’ll see quite a jump in the temps today.  At least 8-10 degrees.  So I think it’s quite likely we hit 90 at PDX, maybe a few notches warmer in a spot or two.

Cooler weather returns Friday and beyond.  In fact the ECMWF says below normal temps Saturday through at least next Tuesday as another upper-level trough moves down into the Pacific Northwest.  You can see the below average 850mb temps (temp in celsius at 5,000′) through the 9th…pretty good agreement on that on the ensemble chart here:


Check out that trough on Monday morning.  500vty_f108_bg_NA  This says SHOWERS to me just looking at the pattern only.  Yet it is early August (not June or September) so models want to keep most/all of the showers north of the Columbia River in the lowlands and in the northern half of Oregon in the mountains.  Take a look at the ECMWF rain total ending Tuesday:


The GFS is slightly wetter with 0.10″ extending down into the Northern Willamette Valley.


The rain showing up south and east of the highlighted area is thunderstorm action east of the mountains not directly related to the cool showers coming in with the trough.  For those of you planning on camping in the northern Oregon Cascades or Washington (me) Sunday-Tuesday, it appears to be another cool and possibly showery early August period.

Chief Meteorologist Mark Nelsen