Soaking Rains Likely: After An Incredibly Dry Summer

August 25, 2015

11pm Tuesday…

There’s good news…it’s looking more likely that we actually have a soaking coming this weekend.  Check out the latest numbers from several different models.


Looks wet doesn’t it?  We need it.  There is a very good chance this will be our wettest period since back in April & May. Check out the rain totals IN THE PAST 12 WEEKS!


Hard to believe we’ve seen less than 1/2 inch of rain in some parts of the metro area in the past 3 months!  May was unusually dry too of course and that’s why our trees/shrubs are suffering.

Confidence has gone up now with a good soaking late Friday through the weekend.  Very high precipitable water content, around 1.00-1.50″ will ensure plenty of moisture to work with as a cold front moves across the area Friday night.  Then several more waves of rain & showers continue through Sunday.  The WRF-GFS is especially wet, showing widespread 1.20″ and above over western Oregon with some areas getting more than 2.00″,


Seems unlikely, but history tells us it CAN happen in August.  Late August 1977, 1983, 2004, etc… those were all big soakers.

It’s nice to be able to leave things outside for weeks at a time and not worry about them getting wet, but that will end early Friday…showers may show up as early as commute time Friday evening.

Chief Meteorologist Mark Nelsen

Big Fires: Oregon Fire History

August 24, 2015

11pm Monday…

The Okanogan Complex in Washington is now the state’s largest fire in history.  256,000 acres and still growing.  You may remember that last year’s Carlton Complex was the largest in the state’s history since the Yacolt Burn in 1902.

So how big have they been in Oregon?

The Silverton Fire in 1865 is the largest on record at just shy of one million acres!


By the way, for those of you not inclined to acres…it takes 640 acres to make one square mile.  So that fire burned about a 40 by 40 mile square!  Wow.

That was during a time of extremely large fires…from 1850 to around 1900 there were repeated huge burns in the Coast Range.  I didn’t even bother to put two more huge fires in the Coast Range from the late 1800s on the chart.  I had forgotten about the huge fire in SE Oregon 3 years ago…of course that was mainly rangeland, but a lot of acreage in just a few days!   The first big Tillamook Burn charred just over a quarter million acres in 1933 too.

After a huge firestorm in Idaho and western Montana in 1910, the USFS went to a “put out all fires” mentality for a long time so massive fires mostly disappeared in the Coast Range and Cascades.  Whether that has increased fire problems nowadays is well beyond my area of expertise (weather).  Someone else can tackle that subject.

The cooler and hopefully wetter weather coming up this weekend and early next week MAY really dampen the current fires.  We’ll see.  I see a bit of a drier trend in models the past 18 hours.  We’ll see.

Chief Meteorologist Mark Nelsen

Open The Windows! Air Quality Good in Portland This Evening

August 23, 2015

10:40pm Sunday…

Whew…good news!  Things are changing quickly this evening in air quality news.  Just as models were showing, the onshore flow this evening is shoving the smoke to the east and air quality is rapidly returning to normal.  Take a look at the current values of Air Quality Index which have all been dropping through the evening.  In fact just as I was typing this up at 10:30pm, it suddenly went to GOOD category in Portland…very nice.


Note many locations are already back to normal but some spots are taking longer to clear out, mainly eastern sections of the western valleys and Cascade foothills.

Enjoy the fresh air, the sun should look a LOT brighter tomorrow!

Chief Meteorologist Mark Nelsen

Yuck! Thick Smoke Over Metro Area Today

August 22, 2015

I mentioned last night that smoke from Washington fires would move in on east wind today but this is the thickest I’ve ever seen in the metro area.  It’s nothing new this time of the year in other parts of the Northwest; but it just happened to be directed right at us today instead of east of the mountains.  This is normal at times in Bend and other eastside cities in late summer.  This is what it looked like at midday overhead:


Overnight and tomorrow the smoke will thin some, but it’ll still be hazy like we’ve seen a few times over the past several weeks.  Then a westerly wind will push just about all the smoke out of here starting about 24 hours from now.  By tomorrow evening skies should be much improved.

 Air quality was just about the worst I have seen in the metro area in summer too; you can see the sudden increase in pollutants after 11am:


This is the first time I’ve busted a forecast because of smoke…we didn’t get hot weather today because too much sunlight was blocked.  Only reaching the mid-upper 80s.  Less smoke tomorrow should mean warmer temps.

Chief Meteorologist Mark Nelsen

Hot & Smoky Weekend Ahead & Much Warmer 7 Day Forecast

August 21, 2015

6pm Friday…

The lack of fire smoke west of the Cascades has been nice the past two days, but it’ll be back this weekend.  Take a look at the latest U.S. Forest Service BlueSky smoke dispersion model:

A couple of still images show smoke from big fires in northern Washington and the Cougar Creek fire on Mt. Adams heading to the east-southeast right now:


Then as our wind switches to northeast and easterly the next 24 hours the smoke is carried right into Western Oregon and SW Washington during the day Saturday.


That smoke will be pushed back out of our area again late Sunday and Monday as the flow turns weakly onshore again so at that point haze should diminish again.

So how warm will it get this weekend?  It’s obvious we have a pretty decent easterly wind flow through the Gorge tomorrow…maybe 3 millibars.  You can see the solid offshore flow during the daylight hours Saturday on the 4km WRF-GFS cross-section.  Note time goes from right to left.  This morning is on the far right side, Monday afternoon on the far left side:

Winds will probably be gusting around 40-45 mph at the Vista House wind gauge tomorrow morning-midday.  Gusts 15-25 mph on the east side of the metro area midday as well.  850mb temps climb to around +18 or +19, which according to my chart means a high temp 90-95 degrees.  I figure we need to knock off a couple degrees for loss of sunlight due to the smoke, so I have gone with a high temp of 92 at PDX.  Sunday maybe just a notch or two cooler, but still we probably will add 1 or 2 more days to the 90+ count for this year when the weekend is finished.

The big change to the forecast is for next week.  Models are definitely struggling with what’s going on in the Pacific, and the Ridiculously Resilient Ridge.  They HAD been advertising a cool trough coming down and hanging around for an extended visit along the West Coast.  But in the past 24 hours they have steadily been pushing the low farther and farther offshore with each run.   The 18z GFS has now gone as far as suggesting we stay very warm with maybe another 90 or two returning the latter part of next week!  Take a look at NEXT Saturday, the 29th from last night’s GFS run vs. the latest.  See the difference?



The unprecedented dry weather will continue; we’ve only seen .12″ rain so far this month.  I am starting to see young trees dying (fir trees turning brown) on the sides of the freeways on my daily commute…water your trees!

Chief Meteorologist Mark Nelsen

It’s The Hottest Summer Ever In Portland…Less than 2 Weeks to September!

August 20, 2015

You are living through what will likely be the hottest summer ever recorded in Portland.


Meteorological summer only has 10 days left (June-August).  As of now we’re running almost 3 degrees WARMER than the next closest contender (2009)!  In fact we would need to have an average high around 72 and low each night around 50 for the next 10 days to cool our average temperature down to 2009 levels. So…

2015 is going to end up as the hottest summer we’ve ever seen


Airport records go back to 1940; and downtown numbers go back to the late 1800s.  But the downtown observation was moved around quite a bit, including up high on roofs (not a good idea), so I don’t put a lot of faith in those earlier numbers in the summertime.  You can get a general idea if any other summers have been close by looking at the entire Climate Zone #2 here in Oregon; that’s all lower elevation locations between the Coast Range and Cascades.  Check out the NCDC data back over 100 years…the June-August average temperature:


Several things stick out:

  1. Before 1958 there are no obvious contenders for really hot summers like we have now.
  2. 1958 is a close call but likely cooler than this year.  Here in Portland, Summer 1958 was hot but nothing like this year.
  3. As I mentioned in a blog post last September, our summers are definitely turning warmer.  Just since my teenage years (1980s), our summer weather has been warming about 0.5 degree per decade.  That’s 5 degrees/century IF that pace were to keep up! Obviously 35 years is a relatively short time period so you have to be careful.

Now before you get too excited about some sort of cataclysmic oven about to descend on the Pacific Northwest in the next few summers, take a look backward first.  Remember these 3 warm, then hot, summers follow 3 very cool and cloudy summers.  Remember how many of us (including me) wondered if this was some sort of change in our climate?  I even constructed a (small) greenhouse for growing tomatoes at my home since the garden was a part failure for two of those years.  Now it’s payback time.

We’ve seen a highly anomalous (unusual) pattern of high pressure lingering near/offshore the West Coast.  As regular readers of this blog know, this has been going on for 2+ years.  That includes the warm blob of ocean water offshore.  There is no reason to believe this is a “new normal” and no current research to suggest that.

So no, this is not the beginning of a sudden change caused by global warming and one should not make a (big) leap to a conclusion that all our future summers will be just like this one.    That said, there is a clear upward trend in that chart above.  With more warming anticipated globally over the next few decades, most likely there fewer very low dips in that chart and more high spots.  We’d better learn to adapt!

Chief Meteorologist Mark Nelsen

ECMWF Weekly Maps

August 20, 2015

I had the last 3 days off, but back just in time for some new weekly 500mb height anomaly maps from last night’s ECMWF:

Week 1


Week 2


Week 3


Week 4


This would imply the next two weeks will be cooler than average with troughing nearby.  The 12z also shows the same thing through the next 2 weeks.  Summer might “end” a bit early.  By that I mean we might see an extended period of normal to below normal temps…maybe.  Either way it’s obvious that the real heat of summer is behind us.

Chief Meteorologist Mark Nelsen


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