Wet Weekend Ahead

September 30, 2016

9pm Friday…

Things have slowed down a bit at work this evening so time for a blog post.  I haven’t been posting as much lately for a few reasons.  The most obvious is that it’s a very slow time of the year weather-wise.  Not much to talk about.  I’ve also been busier the past two months since we were short a weather person.  Well, now we’ve hired a very nice Marja Martinez and she’s all up to speed this week.

By the way, if you aren’t following me on Facebook…

or Twitter…


then you ARE missing regular weather updates.

Why?  Because as you can see I often post quick images or links quickly to those two social media outlets that don’t make it onto the blog.  It’s much simpler than starting up a blog posting.  Yes, yes, I know social media can be extremely annoying and there are privacy issues as well.  But don’t worry, someone is probably tracking your every view of this blog posting too.  For convenience I’ve also added these feeds to the right sidebar over there >>>

For example, I posted this incredible timelapse from Mt. Hood last night:

September ends in just a few hours and it has been somewhat unremarkable.  Temperatures have been near average and so has rainfall (click for better view):


So now we head into October.  There is more change in October than in any other month in the Portland area.  Temperatures fall like a rock during the month.  At least it’s fast for the mild maritime climate we live in.


4 of the past 6 Octobers have been quite wet here.  The last two have been real soakers:


Of course you probably remember the urban flooding on Halloween last year, just about 2″ of that October total fell in the last day!

This weekend we have an upper-level low sliding by just offshore.  It’ll be sending impulses of rain showers up over mainly Western OR/WA this weekend.  Lifted indexes and CAPE values suggest thunder IS a possibility either day this weekend.  Tomorrow we get the usual southwesterly flow spring-type showers.  Sunday is a bit more interesting as the low slides in to the south.  We briefly get into a south-southeast flow before the showers finally end in the evening.  That setup can be good for convection/thunder as well.  So be on the lookout and keep a close eye on the radar this weekend.  Here is our RPM rain total forecast for the next few days.  Not exactly huge rain, but a nice soaking again to gradually ease us into the wetter time of year.


This plus the beginning of October means you can turn off your lawn sprinklers.  Keep an eye on hanging baskets or pots on your deck, but even they should be fine without water for at least the next week.

Enjoy the weekend!

Chief Meteorologist Mark Nelsen



Warmest in a Month Today

September 26, 2016

9pm Monday…

What a “scorcher” by late September standards…many of us in the western valleys hit 90 today; quite rare the 2nd half of the month.

Here in Portland the official high was 89 degrees:


Not quite a record, but close, and right on our forecast of 88-89 the past few days.  That always feels good.  Here are some other numbers around the west side of Oregon and Washington:


Models did very well with this one, both GFS and ECMWF kept pegging a high temperature in the western valleys around 90 degrees (or slightly below) for at least the last 4-5 days.  850mb temperatures peaked out at +22 over Salem this morning which was forecast as well.  Easterly flow was quite weak yesterday, but right on the 2-3 millibar forecast today.

Moving on, we have a nice marine push along with a weak cold front coming inland tonight.  That means a good 10-15 degree drop in high temps.  We’ll end up in the low-mid 70s.

The next 3 days look quite uneventful, then we go into a wetter pattern for the first week of October.  Take a look at the ECMWF ensemble rain forecast for the next 10 days:


Those green bars along the bottom show the ensemble average and the blue is the operational model.  Basically rain gradually accumulates starting sometime late Friday through at least the middle of next week.  The 18z GFS was similar with plenty of wet weather this weekend through early next week.  Snow levels will drop to around 5,000′ too so we may see at least a dusting of snow down to Timberline Lodge.

Finish up your outdoor projects by Friday morning!

Chief Meteorologist Mark Nelsen





Last Weekend of September: Looks Great!

September 23, 2016

7pm Friday…

Today was a cool & cloudy day, but at least our rain forecast was on the wet side.  In the end it rained very little with just light sprinkles/showers at times.

plot_rain_orwa_autoplot It wasn’t exactly a “windstorm”, but we did see the strongest gust in about 6 weeks here in Portland.  We saw a gust to 27 mph.  Coastal gusts were in the 30-50 mph range…a sign of the wind season to come!

The day started with one of those fantastic Mt. Hood shadows that extends UP onto the clouds.


I love that view! It comes from the sun below the horizon shining up through mainly clear skies east of the Cascades.  That first sunlight hits the top of the mountain only, projecting a shadow up on to the increasing high cloud cover spreading in west of the Cascades.  This pic was from Clifford Paguio (you probably figured that out already).

By the way, I was a bit lax this week in posting, partly because the weather was slow early in the week but also because we’ve been busy training a new employee Marja Martinez.  She comes to us from the Telemundo station in Houston.

Looking ahead, a strong upper-level ridge develops directly over the Pacific Northwest over the next 48 hours with 500mb heights up over 590 dm.  That’s a mid-summer quality ridge!  850mb temps soar from +5 tomorrow morning to +20 by Sunday afternoon!  We get about 3 millibars of easterly flow over the Cascades and through the Gorge Sunday afternoon through Monday morning.  Definitely not strong offshore flow, but with such a warm atmosphere overhead that should push our high temperatures into the 85-90 degree range both days.  Those will not be record-setting days since we’ve been as warm as 92-95 during this period.  I checked that 2003 record (95 on the 27th) and found it was +24 at 850mb over Salem with a good easterly flow.

Beyond Monday, we go back to onshore flow quickly and temps return to a more typical 68-75 degree range for the last few days of the month.  The GEFS ensembles and ECMWF both show a cool pattern for later next week and into the early part of October.  Check out those temps dropping off a cliff in the ECMWF 850mb ensemble chart as a cool upper-level trough comes out of Alaska and down over the Pacific Northwest the first few days of October!


Then the 16 day GEFS ensemble forecast temps for the surface here in Portland:


I’m pretty sure we’re done with the 80 degree weather after Monday!

Enjoy the last weekend of September…

Chief Meteorologist Mark Nelsen


XTREME Orographic Weekend

September 18, 2016

Yes, I know, I didn’t spell EXTREME right, but it’s a more dramatic headline that way isn’t it?

The past 36 hours has been a “textbook case” of what we call the “Orographic Effect” caused by “Orographic Lift”.  No, not orthopedic lift, like shoes, but OROGRAPHIC.  Orographic lift means lifting related to topography.

We happen to have a large mountain range oriented north/south through Oregon and Washington (Cascades), and a decent chunk of the year we get westerly wind flow between 2,000 and 10,000′.  When that air is forced to rise over a mountain range, it cools and has to drop its load of moisture in the form or rain or snow.  Then on the back side of the mountain range the opposite occurs.  The air warms and dries as it moves downhill.  Thus enhanced rain on the “up wind” side of the mountains and less rain on the “downwind” side.


You can see the strong westerly wind on the Troutdale wind profiler over the past 48 hours.  Time goes from right to left (most current is left side).  Sea level is the bottom, and the chart goes up over 15,000′.  I’ve highlighted the main elevations we care about for that lifting over the Cascades.  In winter it’ll be even strong than these 25-35 mph speeds for an even stronger effect.  On the flip side we don’t have such a warm/humid airmass in the winter.


When there is plenty of moisture, as there was this weekend, the difference in rain totals can be HUGE.  Take a look at the numbers from west of the Cascades



Yes, you are reading those numbers correctly! 6 TIMES AS MUCH RAIN fell on the west slopes of the Cascades compared to the west metro area.  Notice rain in this pattern picks up as you move east across the metro area.  The air stream is already “feeling” the lifting over the Cascades piling up in front of it as it passes over the metro area.

The heaviest totals are generally just west of the Cascade crest, which in this case is the Hood River/Multnomah/Clackamas county line.  That extends from Mt. Hood north to the Gorge.  Portland’s water supply (Bull Run Watershed) was wisely chosen to come from this area over and west of the crest.  It’s extremely rare that water is in short supply for a whole year in this area.  Even most dry winters will end up with a wetter spring for recharging the reservoirs/lakes.

Once that air moves east, the opposite occurs.  The air moves downhill and dries out.  Check out Parkdale and Hood River’s totals…yes, only a quarter inch or less!


There was about 10 times as much rain just 15 miles west of Parkdale!  Anywhere east of the Cascade crest is in what we call a RAIN SHADOW.  The mountains are “shadowing” those areas from the rain.  This explains the progression in tree types from fir to pine to oaks to no trees and just sagebrush as you drive from Cascade Locks to The Dalles through the Gorge.  The same thing happens when driving through the Cascades except you go up and down in that case.

I can anticipate a couple of questions:

  1.  If the wind blows from east to west (opposite direction) is it wetter EASTSIDE?  The answer is YES, if there is moisture available.  But that doesn’t happen often.  There would have to moisture coming from the east/northeast/southeast.  Not much of a moisture source out there.
  2. What if the Cascades were oriented east-west through Oregon instead of north-south?  The answer is that westerly flow wouldn’t cause the big change in rainfall.  In that case it would need to be northerly or southerly wind to make the big increase/decrease in rain.

There you go…now you know why it poured in the mountains but it was just a typical showery day west metro on Saturday.

Looking ahead, this upcoming week will be pretty slow with a weak upper-level low spinning nearby through Thursday.  Just a chance of a shower here and there.  Friday and Saturday it MAY be wetter, but I’m not sold on that for now.

Chief Meteorologist Mark Nelsen

Yes, The BLOB is Back

September 13, 2016

It’s been going on for a month or two, but news that THE BLOB IS BACK is suddenly circulating through the Internet world.  Let’s talk about it:

  1.  The BLOB was named by Nick Bond (WA State Climatologist) well after if formed in late 2013.
  2. It’s a huge area of much warmer than normal sea surface water in the Eastern Pacific (offshore to our west).  It’s not a physical object or hump of water, but appears as a circular “blob” when looking at sea surface temperature anomaly maps.
  3. The blob was caused by persistent high pressure and relatively calm conditions over that area.  An accounting of the event is in Geophysical Research Letters
  4. It persisted for almost 2 years; from late 2013 to mid/late 2015.  The cause was a change in atmospheric circulation, detailed in another paper by UW professor Dennis Hartmann

Take a look at the progression of the blog…first in late 2013:


Then a close-up of the peak in early 2014:


Then later in 2014 (September):


Early 2015, notice it was spreading out and the warmth moved into our coastal waters:


Then to May/June 2015…that huge mass of water was there all during the summer of 2015:


Mr. Blob then died and the leftover warmer than normal water thinned out from late 2015 through this spring.  Essentially the blob died and the leftovers moved around and didn’t have much effect on last winter’s weather that we know of.

Now it is most definitely back from the dead…

Look at the global sea surface temperature map…even a casual observer can see the blob.  It appears to be the most anomalous feature on all of our global oceans!


Here is a closer view…



Note that right along the coast itself temperatures have NOT been warmer than normal most of this summer and are near to below normal right now as well.  That, plus the upper-level pattern, may be what allowed us to have more reasonable nighttime temperatures this summer.  We sure don’t want 8 degree warmer than normal water hugging our coastline in summer!  At least if you don’t like warm and humid weather.

Of course the next few questions:

  1. Where do we go from here?  Will it stick around this winter?
  2. What effect will it have on our fall/winter weather?
  3. Have we switched back to a similar upper-level pattern that brought us those terrible winters 13-14′ & 14-15′ in the Cascades?

I don’t have any good answers to those questions, although I’m worried about #3.    I think this is a total wildcard in an approaching winter that has a very high level of uncertainty anyway.  NOAA cancelled their La Nina Watch last week so we will likely be in “neutral” territory this year.  Anything goes, no La Nina OR El Nino.

Take a look at how different this post-El Nino fall looks in the Pacific compared to the same time after the last huge El Nino (1998).  Right now:


and the same time in the fall of 1998:


Back then with La Nina getting going we have a very cool NE Pacific (except just along the coastline).  Now we have incredible warmth.   It’s disappointing because just a few months ago it was looking like we might have a nice moderate/strong La Nina winter on the way.  Typically we get tons of mountain snow those winters.  Now we’re back to an average winter.  Or will it be something totally different (much colder/warmer/wetter/drier) than what we’ve seen the past 5 years?  I’d hate to be one of those people who have to make a seasonal forecast for the upcoming winter!

Thanks to Cliff Mass and his excellent weather blog for a few pics of the blob I used above.  He has a more thorough explanation of what’s been going on as well on a posting earlier this week.

Chief Meteorologist Mark Nelsen

Cold Nights and Warm Days

September 12, 2016

8pm Monday…

A short post again since I’m doing all 6 shows this evening.  Not much time!

Last night was the coldest we’ve seen so far this early fall in the metro area.  All of us saw lows in the 40s, with some of us making it down into the upper 30s.  Poor Yacolt, all the way down to 36…brrr!


Tonight there is a Freeze Warning for Central Oregon…should be the first killing frost for most of those areas.  It IS time, since in most of Eastern Oregon you can expect your first fall frost in September:


Along the Columbia River and along the lower elevations that first frost holds off until October.  Remember these are AVERAGES, based on a 30 year period.  Some years it’ll happen earlier, some later.  West of the Cascades we tend to see our first frost at some point in October in the valleys between the Coast and Cascade Ranges:


Notice that it’s later at the coastline due to the mild influence of the Pacific Ocean.  You don’t get frost very often when you are right beside a 50 degree ocean!  For sure not anything the wind is coming from the northwest, west, or southwest.  One other spot that has a very late frost is right in the middle of the urban areas.  At PDX, although it is surrounded by lots of open land, that station has an average first frost in early November.  It’s not on the map, but downtown Portland is even later…in December.  Basically in the middle of all that concrete freezing conditions don’t show up often.  The KGW downtown COOP site only averages 16 days each winter below freezing!

Looking ahead, we are in what I would consider some of the best weather of the year.  Cool nights and warm & sunny days.  Yet it isn’t hot, but not cold either.  Goldilocks time I think.  Mainly highs around 80 or so through Saturday and then 60s and 70s beyond that.

For the first time in a couple of weeks models are suddenly in huge disagreement over what happens Sunday and beyond.  The ECMWF is pushing zonal flow (moist westerly wet pattern) over or much closer to us starting this weekend.  The GFS is keeping us dry.  Here’s the issue:  normally we can look at the respective ensembles from each model and that will give us a good idea which model is performing better.  For example if most of the ECMWF ensembles support the GFS solution then you go with that instead of the lone ECMWF operational model.  Yet in this case the 12z model ensembles supported their own models…not real helpful!

For example:

  • 28 of 51 ECMWF ensembles (54%) show at least 0.10″ of rain in Portland by Sunday afternoon.  Only 1/21 GFS ensembles show rain by Sunday afternoon
  • By Friday the 23rd, 28% of ECMWF ensemble members say we will have seen 0.50″ in Portland.
  • 84% of the ECMWF ensembles show rain at some point between Sunday and the following Friday.  ECMWF says SOME sort of rain showers are on the way.


  • Only 3 out of 21 GFS ensembles show that 0.50″ or more by Friday the 23rd.  GFS says mild and dry weather will continue.

So I did a 7 Day forecast based mainly on the ECMWF with a little GFS (not quite as wet and cool Sunday) thrown in.  The main point is that showers MAY show up on Sunday.

I used this graphic yesterday at 10pm, showing our string of warm Septembers.


So far this month we are running well below normal for the first September since 2007.  We’ll see how it looks a week from now.  We may end up erasing that cold anomaly.  How dare we let Portland end up with a COLDER THAN NORMAL month!  It seems to take an act of God for that to happen nowadays.  But eventually it will happen again, right?

Enjoy the sunshine!

Chief Meteorologist Mark Nelsen



Friday Night Quick Post

September 9, 2016

A real quick one because there is very little going on weatherwise this Friday evening!

It’s very obvious now that the 10 day period of cool weather we just went through will not be repeated for at least the next 2 weeks.  There is no sign of record-breaking hot weather, but we are entering a long period of very stable and warm days with comfortably cool nights.  Many would say the next week or so is perfection for September!

Upper-level ridging will be over us much of the next two weeks, or at least nearby.  Check out the ensemble 500mb heights NEXT Friday from both the ECMWF & GFS.  The colors are the anomaly…we have higher than normal heights (for mid-September) forecast over us:



Pretty high confidence when 2-3 models show the same thing.  Note the 12z ECMWF ensemble forecast 850mb temperatures.  Each line is one member of the ensemble and red is the average.  This goes out to slightly over 2 weeks:


Note it is above normal (green line) most of the time.   Quite a bit of spread beyond next Friday too.  The ECMWF ensemble rain outlook, each horizontal line showing one member of that ensemble:


The average is skewed high by a few very wet members.  I counted, and see 30 of the 50 forecast members have less than .10″ during the next 16 day period.  That’s dry!  The GEFS ensemble shows the mild temperatures continuing here at the surface with above normal through most of the period:


Even at days 15/16 that upper-level ridging is still nearby on the ECMWF/GFS/GEM models.  These maps are all for Saturday the 24th…




So to wrap things up, I’m feeling pretty confident that in general a mild & drier than normal regime will stick around for the next two weeks.

Enjoy the weekend!

Chief Meteorologist Mark Nelsen