Weekend Outlook & ECMWF Weekly Maps

May 15, 2015

11:30pm Friday…

A thick marine layer west of the Cascades sticks around tomorrow, giving us another gloomy day with a few sprinkles.  If you want sun head east of the Cascades.

Sunday the onshore flow weakens dramatically.

7 Day

Monday is an interesting day as a weak thermal (warm) surface trough develops right over us.  Not really an east wind situation, but the effect on temperature should be dramatic regardless.  We might end up around 80 degrees Monday.  The other reason Monday is interesting is because some models show a lot of CAPE and below zero lifted index along with the thermal trough.  A very unstable atmosphere.  That plus easterly upper-level flow and increasing precipitable water screams “THUNDER POSSIBLE” to me.  We’ll see how models develop the situation as we get closer.

These maps are actually from the ECMWF 32 day run two nights ago…sorry, a little slow.





They show upper-level heights rising to a bit above normal over the Pacific Northwest over the next month.  Supposedly the pattern of cool troughs moving in to our south will end; which has been very unusual for May.  This tells me we still don’t have any long cold/wet period coming up, at least west of the Cascades.  Rainfall is still a bit below normal here in Portland at mid-month.  We could end up with a drier than normal May.

Chief Meteorologist Mark Nelsen

Much-Needed Rain In Eastern Oregon & Washington

May 13, 2015

In the drier parts of Oregon and Washington, rain is almost always a welcome sight and last night was no exception.  Take a look at radar estimates of the downpour as the upper-level low passed overhead.


Many areas received more than 1″ of rain and some areas up around 2″.  West of the Cascades this would just be another annoying and wet day.  But in a desert or near-desert environment?  A soaking at the beginning of the growing season is pure gold!  I once had a dryland wheat farmer in Sherman County tell me that he refers to a May soaking as gold falling from the sky.  Or something like that…I forget the exact quote.

Unfortunately north-central Oregon didn’t get in on the action this time around.  Doesn’t look like much fell in Maupin, Sherman County, or Condon.

But there is hope for more because the overall pattern remains about the same for another 7-10 days.  A large upper-level trough lingers along the West Coast and disturbances will rotate through it at times.  That brings a flow of moisture from the south across much of the east side of our states…Idaho too.  We never know exactly where the soaking rains end up until a day or two ahead of time in this pattern but in general it’s a good thing.  Take a look at forecast rainfall the next 8 days from the 00z GFS:


and the 12z ECMWF


Looks good for you folks eastside.  Another inch or two of rain could fall!  Just what you need before June heat sets in.

Westside we have strong onshore flow Friday and Saturday so I see lots of cloud cover but not much rain (if any).  Models this evening are downplaying the thunder threat Thursday afternoon for us now too.  Most of them are keeping us mainly dry tomorrow.  Enjoy the warmer and (mainly) dry day.

Chief Meteorologist Mark Nelsen

A Big Soaking For Some Tonight

May 11, 2015

Monday 5pm…

I was out working in the yard/garden this weekend and it’s pretty obvious we could use a soaking.  Here comes a night with some good downpours, but only for some of us.  The issue is that we don’t know exactly who is getting the soaking tonight; although we have a general idea it’ll be in the far northern part of Oregon and SW Washington.

An “upper-level low” will track from just off the central Oregon coastline at this moment to around Burns by tomorrow afternoon. The combination of moist southeasterly flow ahead of and to the north of it running into the northwest flow behind it will likely form what we call a “deformation zone”.  It’s a solid area of rain that develops in that location, generally north-northwest of an upper-level low.  Here’s the WRF-GFS rain forecast for the next 24 hours:


It’s soaking the Portland metro area with around an inch of rain, possibly even higher.  The pink area indicates 1.28″ or more.  The band of heavy rain appears to be centered from the central Oregon coastline across to Mt. Hood.

Our RPM forecast has similar, or slightly higher totals, but has the main action farther north.


Notice just south of the metro area the totals are significantly lighter.

The HRRR model, which only goes out to 15 hours, has the soaking rains even farther north.


Note only a few sprinkles south of the Columbia River by sunrise…seems too far north to me based on what we’re seeing on radar so far.

So the big picture is that a large area somewhere between Eugene and Olympia should get a soaking within the next 24 hours.  Regardless of the totals, Tuesday appears to be a rainy and cool day for most of us.  In fact I don’t see a good chance for dry weather activities (that need many hours of dry weather) until the 2nd half of the week.


We have two more upper-level lows that move inland over the West Coast, one on Thursday and one Sunday.  Both of those are moving into California, which means not a lot of rain here.  We could still see showers after Wednesday, but they should be far more spotty.

Chief Meteorologist Mark Nelsen

Low, But “Warm” Rivers This Weekend

May 8, 2015

There is one benefit to the lowest winter snowpack in decades…rivers are running warmer than normal.


The Columbia River is 4 degrees warmer than last year on this date.



The Willamette and Clackamas rivers are also warmer than one year ago.  If you regular walk, drive, or fish from a local river you’ve probably noticed how low they are running too.


In fact many west of the Cascades are near their lowest ever recorded for early May; many of our rivers look like they typically do in late summer.  Several rivers draining the west slopes of the Cascades are in the lowest 10 percentile of years.  Very unusual conditions for early May indeed.  Rainfall the past month has been less than 50% of average for most of Oregon.  Add that to the already low snowmelt feeding into rivers and this is what we get.

Enjoy the sunshine this weekend.  It’ll be our warmest weekend of 2015 so far…

Today we made it to 80 degrees (possibly slightly higher) in Portland and tomorrow should be a notch or two warmer.

Chief Meteorologist Mark Nelsen

May Begins Mild & (Mainly) Dry

May 5, 2015

9:30pm Tuesday…

It’s been awhile since I last blogged; but I’ve got a few random notes tonight:

1.  Mt. Bachelor is closing.  They are the last ski area to throw in the towel on the horrid ski season.  They typically stay open daily through Memorial Day since USUALLY there is plenty of snow left on the ground.  Not this year!  You can read all about it on their web page.  This coming Sunday will be the last day.  http://www.mtbachelor.com/site/winter/ski/update


2.  Detroit Lake has stopped filling.  I noticed the level hasn’t changed in a week; it appears the very low flows on the streams feeding into the lake aren’t keeping up with the discharge.  That’s due to little rain and hardly any snow to melt.  A neat graphic here shows the leveling off.


Rainfall has only been around 50% of normal for much of Oregon in the past 30 days.


This is exactly what you DON’T want after the worst snowpack on record.  Forecasts of decent stream flow across parts of the state have been based on NORMAL precipitation in April and May, before the dry season really kicks in.  If May continues dry, we’re probably even going to see some issues on the westside of the state too.

3.  Split-Flow and/or Ridging seems to want to hang around.  Here is the forecast for next Monday from tonight’s GFS:


A pattern of systems cutting off and dying as the approach the West Coast has been causing problems with models in the 5-10 day range.  The warm stretch we just had late last week and over the weekend was forecast very well way out in time.  Over the past couple of weeks models have repeatedly shown cool/wet conditions in the long-range only to have the splitty pattern reappear.  That seems to be happening again for this coming weekend and early next week.  Some of that is not unusual in the spring season, but it IS strange to see upper-level lows diving down towards California in May.

The 12z ECMWF Ensemble 500mb height anomaly for NEXT Wednesday shows the troughing to the south…


But ridging returns to our north again mid-month, note Monday the 18th…


I have a feeling May is going to return us back into “Above Average Temperature” territory.

4.  Short term we have a chance for thunderstorms tomorrow afternoon/evening, although most action appears to be over the mountains.  There’s always a chance that we get something to drift out over the valleys though so maybe we’ll get lucky.  Today was sure underwhelming with many spots getting very little rain.   Then it’s back to 70s and maybe even touching 80 for Friday and Saturday.  It appears we have ANOTHER very nice weekend ahead.  Moms will be happy with that.

Chief Meteorologist Mark Nelsen

Siberian Smoke Likely Back For Bright Orange Sunrises & Sunsets

April 29, 2015

10pm Wednesday…

Did you see the sunset tonight? Some areas were clear enough that we could see a very orange sun as it sank to the horizon. It appears another “cloud” of smoke/haze is back…most likely from fires in Siberia. Here’s the 6pm smoke discussion from NESDIS:

…A large area of unknown aerosols is moving in from the Pacific Ocean over the US Pacific Northwest and southwestern Canada. Models suggest this area may contain blowing dust from Asia as well as smoke from Siberian fires…

And a blog from NASA says the smoke is moving across the Pacific on the east-flowing jet stream.  Here’s a quick screen capture:


So enjoy the bright sunsets we’ll probably see the next few days.

Chief Meteorologist Mark Nelsen

82 Degrees Monday: Warmest This Year

April 27, 2015

Quite an April “scorcher” out there today:


The 82 degree high at PDX was above our forecast of 80 degrees.  Not quite a record (86 in 1987), but 18 degrees above average!  The Salem sounding at 5pm showed an 850mb temp of +14.6 degrees.  In non-meteorological jargon: The temperature around 5,000′ elevation over Salem was about 58 degrees.  It could have been even warmer;  my chart for April shows easterly flow, solid sunshine, and a +14 has seen a Portland high temp as high as 85!  Models had shown +12 or +13, thus the forecast of 80.

Maybe more amazing is the jump from yesterday.  The high temp jumped 21 degrees in one day, which I haven’t seen happen in the spring.  Of course we’ve seen it drop 20 degrees in one day (tomorrow?) due to a major marine push and/or a cold front passage.

The easterly pressure gradient has increased this afternoon and evening, giving a peak gust over 50 mph at Crown Point and 40 mph at Corbett.  It’ll back off dramatically by sunrise as low marine clouds flood into the valley.

We’ve got a weak cold front moving inland tomorrow so expect some showers but not a big soaking.  In fact I don’t see any other decent chance for rain in the next 7-8 days.  This might be a year in which we start watering in May unless a trough materializes the middle of next week with a nice soaking (.50″ or more).  Both the 18z GFS meteogram and 12z ECMWF meteogram showed less than 1/2″ in the next 7-10 days.



It does looks like a very mild and “settled” weather pattern over the next week.  By that I mean that after tomorrow’s disturbance moves past we see the action lift north.  This is typically what we see later in May and June.  So temperatures warm to above average over the next week.  This may be a re-emergence of the ridging we’ve seen so often over the past year or so.  Take a look at last night’s ECMWF monthly run.  One map representing the average height anomalies for each week.





Same sort of splitty pattern we’ve seen recently with lower than normal heights to our south and higher than normal to our north and northwest.

Chief Meteorologist Mark Nelsen


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