New Year Brings Big Gorge Wind

December 30, 2015

11pm Wednesday…

The sunshine has returned but so has the chilly Gorge wind.  Today the wind was just “average breezy”, but the next few days it’ll be a totally different story.


Strong high pressure develops east of the Cascades Thursday-Sunday.  That means the pressure difference from eastside to westside dramatically ramps up the next 24 hours.  East wind increases as well.  That wind rushes through the one near sea-level gap in the Cascades; the Columbia River Gorge.  That’s why it’s called a “gap wind”.  The peak of the wind seems to be centered on New Year’s Day.  How windy?


Those 65-80 mph gusts are for the usual windy places in the Gorge, not Crown Point.  Friday-Sunday should be 100+ mph days at Vista House.  It’ll be about 10 degrees colder than we typically see on these big wind days so you geeks headed out there better bundle up like you are in the Arctic!  In the metro area gusts 35-50 mph are likely Friday-Sunday from I-205 east.  Elsewhere, as always with a gap wind, the wind will be mainly light easterly, or at least less than 10 mph.

The WRF-GFS cross-section shows 50-60kt. wind just off the surface.  That’s just about the highest you ever see on these cross-sections:

The chart was slightly “windier” for the Veteran’s Day Windstorm in November 2014.

I missed today’s high temp forecast by 4 degrees…it was 44 instead of 40.  I should have known better, the first east wind day when cooler air arrives is usually warmer than expected.  Then things settle down and the inversion settles in.  Temperatures drop a few degrees on following days.  Sure enough I notice areas in the wind tonight are running 2-3 degrees cooler than last night at this time.  So not only will be it windier tomorrow in much of the metro area, but it’ll be cooler as well.  Brrr!

I’m taking tomorrow off, so stay warm and have a safe and happy New Year’s Eve!

Chief Meteorologist Mark Nelsen

Northern Lights Possible Tonight

December 30, 2015

Very late tonight and again tomorrow night there is a chance you could see the aurora borealis or northern lights.  Note I wrote CHANCE.  I have still never seen them even after telling viewers multiple times that a CHANCE is on the way “tonight”.  Why?  Often they just appear for a few minutes or dozens of minutes at a time and then disappear.  Sometimes they don’t appear at all in our skies even though a geomagnetic storm is in progress.  Just to throw a number out there, if you were to go outside late tonight and stare up at the sky for 5 minutes out in the country…you probably have a 5% chance of seeing the northern lights.  Out of the ENTIRE night NOAA guesses we have about a 50% chance of seeing them at some point during the night.  Seems like aurora forecasting is about where weather forecasting was 100 years ago.


As of 5pm the storm has not yet arrived.  So don’t even bother in the next few hours.  Keep an eye on to see what’s going on elsewhere across the Northern Hemisphere.

You can find the latest planetary “K” index at this website:

It’s a measure of geomagnetic storm activity.  When the level jumps to 6 & 7 that’s a big storm.  As of 5:30pm it’s all quiet and the storm has not arrived. Keep in mind that the times are in UTC…which is 8 hours ahead of us.  So we’re actually 1 hour 30 minutes into December 31st in UTC time…got it?


Chief Meteorologist Mark Nelsen

The Wettest Month Ever in Portland

December 29, 2015

It has finally stopped raining!  Here are (what should be) the final numbers for December 2015.  Wow…

BMAC Rain Two Day Total

The only 3 days without measurable rain will be the 26th, 30th, and 31st.

This blows away the previous wettest month of all-time at PDX, which was 13.35″ in December 1996.  The records go back to around 1940 at PDX.  That’s a 75 year period.

Now over the past few weeks I’ve had several people email (one called…yep, old style communication!) that I was missing the older records and it sure isn’t the wettest of “all-time”.

  1. It is at the airport.
  2. It’s quite possible it’s the wettest month downtown since the 1882.  Most likely it’s the 2nd wettest of all time downtown!

Here’s the problem:

  • Records HAVE been taken at various downtown locations since the early 1870s
  • Downtown over time has shown to be about 15-20% wetter than the PDX location.
  • As a result you can’t compare both locations directly.
  • Rainfall observations are tougher to screw up than temperature, so I do feel pretty good about using those numbers, even though I think downtown temperature records are a bit more suspect in the past.

What does Downtown show?  Here are the 3 wettest months:


So how much this month?  Short answer is…we don’t know.  The official observations are sent in once per month and this month hasn’t been sent in yet of course.  One more reason I rarely mention downtown weather stats…quite a time lag.

Preliminary data IS available, but in the case of this month there are lots of days missing:


There are 10 days missing in this data for downtown.

So let’s do some guessing at what the total might be.  The total WITH the 10 days missing is 14.42″.  If you take just PDX numbers for those missing days and plug them in, the total would rise to 17.86!  Remember that’s using the “drier” PDX numbers.  If you increase those missing days by 15% (because downtown is typically 15-20% wetter), then the monthly total would end up at 18.38″.

As a result, I think most likely this month was the 2nd wettest on record in downtown Portland and the wettest since 1882.  

That’s the wettest in 133 years!

Chief Meteorologist Mark Nelsen


More Precipitation = Lower Snow Level

December 29, 2015

10:15am Tuesday…

It’s rare, but I was actually surprised by a dumping of snow out the window when I woke up this morning.  About 1.5″ new so far.  Now I live at 1,000′ just east of Corbett, but I see snow is falling (not sticking) even into the east metro area near the Gorge.  That’s due to slightly drier/cooler air out there.

Models didn’t show this much moisture making it north, and as of now I don’t see the precip suddenly changing over to snow for most of us.  BUT, the snow level near the Gorge at least is right at 1,000′ at this hour.  Notice it’s been dropping from 1800′ to 1100′ the past few hours on the Troutdale profiler:


I don’t think the snow level will get much lower since we don’t have a cold/dry source of air flowing through the Gorge.  That said, offshore flow increases through the afternoon/evening as the low pressure offshore slides to the south.  I’ll be watching closely!

Showers will taper off this afternoon/evening and then we go dry/cold the rest of the week as mentioned in the previous post.

Chief Meteorologist Mark Nelsen

Best Christmas Vacation Skiing in 3 Years!

December 28, 2015

9:30pm Monday…

What a run of snow in the Cascades the past 2 weeks or so!  The result has been the best snowpack for late December we’ve seen since December 2012.  Note the snow depth at 5,400′ (Mt Hood SNOTEL site) the past few years on yesterday’s date:


And that means the snowpack is ABOVE normal across the entire state of Oregon!  The best news is across the southern half of the state: almost double the typical late December snowpack right where we need it.  This will ease the drought quite a bit, especially if we get normal or better snow down there the rest of the winter.


A dramatic change has occurred though, models are showing a very dry pattern for the next 10-14 days…well into the 2nd week of January at least.  A weak system just misses us tomorrow, we’ll get a few showers but that will be it.  Otherwise upper-level ridging will develop later this week over and north of our area.  That will divide storms and/or send them to the north.


The result will be warmer than normal temps in the mountains over and west of the Cascade crest.  In the lower elevations and east of the Cascade crest…well, it’s mid-winter and that means big-time inversions developing later this week.

We do have a situation in which we’ll see stronger and colder than “typical” east wind through the west end of the Gorge and metro area too.  That’s because the vast majority of the Pacific Northwest is covered in snow.  Take a look at the snow cover map today, which obviously isn’t perfectly accurate since we know there is no snow on the ground in the Tualatin Valley!


It’s probably fair to assume the areas that show less than 2″ on the ground don’t actually have any on the ground.  But the point is that most areas east of the Cascades are cold and snow-covered.  With strong high pressure developing Wednesday and beyond, we’re going to see 10-14 millibar easterly gradients through the Gorge.  Probably Thursday-Saturday will be 100+ mph days at Crown Point, with temperatures only around 30!  Too cold for me , heck, I was freezing up there when it was in the low 40s.  Lots of ice on Gorge waterfalls by this weekend as well.  Gentlemen…start your cameras!

Here in the metro area the combo of the wind and chilly air will give us the coldest weather so far this season.  In fact if we don’t have an arctic blast in the next 6 weeks, this may quite possibly be the coldest weather of the winter.  Calm areas should drop into the 15-20 degree range Thursday and beyond.  This should be mainly a “gap” wind event with strong wind confined to the usual east wind spots.

I am very confident we do have lots of sunshine ahead Wednesday through at least this coming Sunday.  It’ll just be cold!

Chief Meteorologist Mark Nelsen

ECMWF Monthly Run

December 28, 2015

Looks like ridging or split flow is here for the next 2 weeks.  Definitely an “El Nino” look.  We’ll see about the 2nd half of January.  These are ECMWF weekly 500mb height average maps from last night’s 45 day run.  Warmer colors are heights higher than normal (ridging), cooler colors heights lower than normal (troughing).  This is an average of all 51 ensemble members:

That Was Fun: Metro Area Snow

December 27, 2015

4pm Sunday…

  • It was a bit late getting going, but things turned out almost exactly as forecast (a nice change).
  • Accumulation on roads was only in higher elevations closer to 1,000’ and above…West Hills, Mt. Scott etc…  I saw a report of 2” around 1,000’ in Forest Heights area (thanks Mikayla)
  • Accumulation is pretty much done since showers will be on the decrease now through the evening
  • Lower elevations (in cities) was a rain/snow mix depending on where you were. West/northwest suburbs (Hillsboro/Scappoose/Banks) did get some light accumulation and the coldest temps.

ROADS IN THE WEST HILLS ARE SNOW-COVERED RIGHT NOW ABOVE 700’ OR SO.   Pic from Andrew Mork in Forest Heights area:



METRO AREA TONIGHT:  Mixed showers mostly end by 10pm.  Temps hold steady above freezing, might even rise a degree or two in the hills where it is right at 32 degrees,  so FREEZING OF ROADS IS UNLIKELY DUE TO CLOUDY SKIES, but I’ll keep an eye on it.  Any clearing would bring icy spots since roads are wet.

Driving to work between 2-2:45pm was real interesting…totally dry until about Fairview, then flakes got bigger and bigger through Gateway area.  As I got closer to downtown some rain mixed in, but mainly snow.  Going through the tunnel on US26 I entered into a nice winter wonderland of frosted Douglas Firs on both sides of the highway on the climb up to 700′ at Sylvan.  At that point you could see some snow on the exit ramp. But MOST INTERESTING was that within 1/2 mile coming down past the cemetery, all snow on trees and most on the ground disappeared!  Even though it was a higher elevation than down around the zoo to the east and below where there was plenty of snow.  Most likely that was caused by easterly wind piling up colder air against the east side of the West Hills, allowing snowflakes to make it farther down in the atmosphere without melting east of Sylvan.  That’s my guess.  It would only be noticeable in these real marginal rain/snow conditions.  After that it was just a rain/snow mix the rest of the way to the Cornell Exit where FOX12 is located.  Good geeky stuff

More later…

Chief Meteorologist Mark Nelsen