October 26, 2018
Hey folks,
It’s time again for the annual Winter Weather Forecast Conference at OMSI.  It’s coming up tomorrow at OMSI.  I’ll be presenting my usual recap of the past winter.
Mark OMSI Forecast Meeting Promo
All the details are on this media release from Oregon Chapter AMS:

26th Annual Winter Weather Forecast Conference

The Oregon Chapter of the American Meteorological Society (AMS) will host the 26th annual “Winter Weather Forecast Conference” on Saturday, October 27th @ 10 AM @ OMSI in Portland. Meteorologists from across the Pacific Northwest will once again converge on Portland to give their annual forecasts for the upcoming winter to a capacity crowd of nearly 300 attendeesWhat lies ahead this winter with the likely return of El Nino? Come hear the latest details. The Oregon AMS chapter will also be raffling off a $200 voucher to the Tolovana Inn Resort in Cannon Beach, along with a $300 Davis home weather station. This meeting is free and open to all ages of the general public.   

What: 26th Annual Winter Weather Forecast Conference
When: Saturday, October 27th 2018 @ 10 AM.
Where: Oregon Museum of Science and Industry (OMSI) main auditorium, 1945 S.E. Water Ave. in Portland.  
Meeting and parking cost: This meeting is free and open to all ages of the general public. Free parking in all OMSI parking lots.
Agenda: Meteorologists from across the Pacific Northwest will once again give their weather forecasts for the upcoming winter

Who is the Oregon AMS? The Oregon chapter of the American Meteorological Society (AMS) was founded in 1947 and is the single largest local chapter of the American Meteorological Society (AMS) in the country, with approx. 180 members. The Oregon AMS chapter normally hosts meetings from September to May that are free and open to all ages of the general public. The Oregon AMS welcomes the public to become chapter members for just $10 per year. The Oregon AMS chapter mission statement reads, “The purpose of this society shall be to advance professional ideals in the science of meteorology and to promote the development, exchange, and application of meteorological knowledge.” Our meetings are always found on our web site: http://www.ametsoc.org/chapters/oregon

Wet Season Arriving

October 25, 2018

6pm Thursday…

When I think of typical October weather, today would pretty much cover it.  Not a real soaker, but gray and rainy at times.  We’ve picked up about a quarter-inch of rain so far in much of the metro area:

Rain Metro Today Databound

I’ve been expecting a decent amount of rain during the next week, but models are a bit wetter today.  Check out the 7 Day precipitation forecast from the ECMWF, that’s through next Thursday

ECMWF Precipitation Accumulation

Pretty wet!  If this occurs, October will go down as a wet one even though we had two weeks of sunshine in the middle of the month.  This points out how things can change quickly in late October as the wet season arrives.  Notice a few spots in the Coast and Cascade ranges with 6-8″ of rain; this will provide the final soaking to finish off what was left of this fire season.

Sunday could be a particularly active weather day with frequent showers, downpours, and thunder/hail.  It’s a cool and unstable airmass moving overhead that day.  By Monday morning we’re back to that chilly airmass we saw in early October; expect snow down below Timberline Lodge but not quite sticking to the passes.  You see the dip in snow level here:

ECMWF Snow Level From 850mb Temps LONG TERM

By the middle of next week strong high pressure offshore will somewhat shut down the rainfall, or at least slow it to a trickle as we enter November.  One weak system will slide over the ridge on Halloween and that COULD give us a rare wet Halloween evening, we’ll see.  Most of the past 15 years we’ve seen dry conditions during that critical Trick-or-Treat time 5-8pm.

Halloween Weather History

Looking farther ahead, the weather pattern still looks mild and slow later next week and that first weekend of November.  You see the upper-level ridging and mild conditions on the ECMWF ensemble 500mb heights on Saturday the 3rd


There are hints of a cooler pattern just beyond that, maybe 12-14 days from now.  We’ll see, that’s a long way off.  For now I’m still confident that we don’t see a stormy pattern through the first week of November.

Chief Meteorologist Mark Nelsen

Ski Season Update, El Nino, & The Blob Returns

October 24, 2018

8pm Wednesday…

We have an easy week here at FOX12.  That’s not just due to the slow weather, but 5 nights with no early shows due to the World Series and Thursday Night Football. So what else would a weather geek do except plug some numbers into a spreadsheet and make some graphs?

2 weeks ago I posted my thoughts about this upcoming “El Nino” winter, that’s up above on the tab titled WINTER 2018-19 THOUGHTS.   Nothing has changed since that time, except that it seems to be even more a likelihood that we’re entering this kind of winter.  Note the increasing sea surface temperatures the past few weeks (right side graphs)



There is a section in there about ski area conditions during this type of winter that includes this chart


The key points?

  1. El Nino winters are rarely “ski disasters”
  4. El Nino winters are often more reasonable up above 5,000′ or so.

But tonight I wondered what happens EARLY in the ski season.

We’re talking November and December.  My conventional thinking in the past has been that many El Nino winters “begin with a bang”, like Nov/Dec 2006.  Then they often peter out to mild/dry or mild/wet after the New Year.  Apparently that’s not the case much of the time.

Let’s take the last 16 El Nino seasons.  That is my entire lifetime, back to 1969 (getting old).  I totalled November & December snow totals at Government Camp (~4,000′).

The long-term average for these two months is 87″ (35″ in November & 52″ in December)

But during El Nino seasons the average is significantly lower…just 57″, that’s the lower dashed line.  The key message is that in 10 out of 16 years, snowfall was well below average during the first two months of the wet season.

ElNino_November-December Govt Camp Snow

By the way, here’s November 19th snow depth on Mt. Hood near the bottom of Timberline’s Pucci Chairlift for the past 9 winters.  Last year was great…until a pineapple express melted much of that 34″ just before Thanksgiving.  That delayed ski area openings a bit.

Mark Mt Hood Snowpack November

On that chart above you might be wondering what the “M” refers to on some of those years?  Those were “El Nino Modoki” years, where the warm pool of water in the tropical Pacific was centered farther west.  It has been documented that these Modoki events produce different effects over the mid-latitudes than a “typical” El Nino.  Here’s a nice visual showing the difference between the two “flavors” of El Nino:

ElNino_Modoki_SST Look

And here is what we have right now


It sure looks more like a Modoki flavor of El Nino doesn’t it?  That said, I don’t see much real correlation between the early part of Modoki ski seasons and low snow totals.

Of course what really sticks out on that sea surface temp chart is the return of “THE BLOB”.  Take a look at all the “warm” water in the Eastern Pacific!  The past two months have seen a rapid development of “The Blob v2”.  You may remember that for about 18 months in 2014-15 we had a large blob of warm water offshore.  This is what it looked like in March 2015


a closer look at what we have right now…


This time the blob is slightly farther to the west, although it has moved closer to us recently…here’s one month ago


What does an El Nino winter plus tons of “warm” water to our west mean?  I don’t think anyone really knows the answer.  But I don’t think it’s good if you want a cold/wet winter with lots of mountain snowfall.  It COULD be a difficult winter ahead for the ski resorts.  Regardless, I’m going for a season pass for one family member anyway.  Except in the very few bad years, EVERY winter has decent ski conditions off/on through the season.  We’ll see how it goes.

Chief Meteorologist Mark Nelsen

Last of the Warm & Dry Weather

October 22, 2018

6:30pm Monday…

It’s been glorious hasn’t it?  Day after day of sunny skies, cool mornings followed by warm afternoons.  If you’ve lived west of the Cascades most/all of your life (like me), now you know what it’s like east of the mountains in a typical October.  Eastside sees a wider diurnal temperature range and more sunshine in mid-Autumn.

Today is our 14th day without measurable precipitation in Portland.  It just has to be a record right?  Not even close!

Dry Spells October

I remember October 1987; my first year in college up in Centralia.  It didn’t rain until Halloween; poor timing for the little kids.  And of course none of us were around in 1895 when no measurable rain fell the entire month!  So we can have long dry spells in October, but most years just see occasional shorter dry periods.

What’s ahead?  BACK TO NORMAL is what I’m seeing.  Not a sudden plunge into the storm season by any means, but we’ll be “easing in” to cloudier/wetter/cooler weather through the end of the month.  A very weak system moves inland tomorrow and pretty much falls apart, then a little wetter one for Thursday will wet the ground nicely.  Most likely a nice soaker is on the way for Sunday/Monday too.  That’s because our big ridge of high pressure breaks down and is replaced by southwesterly flow in the upper atmosphere.  I figure we could see 1.00-2.00″ in the next 7 days…it’s a start at least.  As of today the past 6 months (mid-April to mid-October) have been the 2nd driest on record in Portland after 2015.

What about mountain snow?  Not yet, this southwest flow isn’t good for mountain snow, especially so early in the season.

ECMWF Snow Level From 850mb Temps LONG TERM

Is this the beginning of a stormy period?  That’s somewhat common to see the last week of October.  But I don’t think that’s the case.  Take a look at the 10 day forecast 500 millibar height/anomaly from the GFS/ECMWF/GEM models.  Red indicates higher than average heights.  All 3 are for November 1st, a week from Thursday

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That’s the same pattern we had earlier this month with a big ridge somewhere in the far eastern Pacific.  This is a drier than average setup for us this time of year.  Whether it’s warmer or cooler than average will be determined by the location.  Regardless, it appears a stormy start to November is unlikely even though October will go out wet.

Keep in mind we are entering an El Nino winter/wet season.  It has been quite a delayed start but today’s weekly ENSO update shows the important Nino 3.4 region is up to 0.9, approaching moderate El Nino status.  You can see the warming on the right-side chart


So what has happened in November in El Nino years in Portland?  I just took at look at the last 10.

LAST 10 EL NINO WINTERS:  1987-88, 1991-92, 1994-95, 1997-98, 2002-03, 2004-05, 2006-07, 2009-10, 2014-15, 2015-16

NOVEMBER TEMPERATURE:  6 of 10 milder/warmer than average, 2 near average, 2 cool

NOVEMBER PRECIPITATION:  6 of 10 drier than average, 2 near average, 2 wetter

NOVEMBER SNOW:  It’s always rare in November of course, and we’ve only seen snow one of those 10 years.  That snow/freezing rain mix in mid-November 2014.  Just a trace officially.   East metro and hills had freezing rain with that very early season freeze.

By the way, I crunched the February El Nino winter numbers too.  I was thinking of a vacation and wondered what the threat of snowy/icy weather could be.

TEMP:  7 of 10 milder/warmer than average, 3 average, None colder than average

PRECIP: 4 of 10 drier than average, 4 average, 2 wetter

SNOW:  Only 1 in 10 had any snow, the February 1995 snowstorm.  Apparently snow in an El Nino winter is very rare!  Booking tickets soon…

Chief Meteorologist Mark Nelsen

A Spectacular Period of October Sunshine

October 17, 2018

8pm Wednesday…

It’s been just about perfect once again today; a cool start then a warm afternoon for most of us.  There was just enough offshore flow today to keep the coastline up in the 70s.  Tillamook even hit 80 once again

Todays Observed Highs OrWa 2017

The weather might seem extra nice because temperatures have done the REVERSE of what we typically see in October.  We started out cool and then warmed up mid-month.  In a typical year temps bump up and down through the month but we head downhill in general.

High Temp Last 13 Days

We were just 4 degrees from a record high today and just 3 degrees away from one yesterday.  Today is also our 9th consecutive dry day; quite unusual in October.  But it has happened in the past!  In October 1987 no rain fell until Halloween.  And way back in 1895 (downtown Portland records) no measurable rain fell all month!

Dry Spells October

Easterly wind has been blowing since Sunday in the Gorge, and has been pretty strong for October the past 3 days.  But the pressure gradient across the Cascades is dying down this evening and it’ll just be a “whisper” of east wind tomorrow and Friday.  At least it’s still a “warm” wind.  I’m quite confident that next time it appears it’ll be cooler.  In fact east wind is always cool/cold from Halloween to early March.

Models have been doing a very good job with the big picture and nothing has really changed in the long-range forecast since my last post Sunday evening.  Strong upper-level high pressure is over the West Coast; it flattens a bit tomorrow, then pops back up over the Intermountain region Saturday through Monday.    This means we still have 5 more days of warm and (mainly) sunny skies.  A weak push of marine air could give us areas of fog or low clouds Friday and/or Saturday morning.  Same thing is possible Monday morning.

Rain is on the way for Tuesday.  Check out the ECMWF ensemble prediction system 24-hr precipitation


That’s a pretty clear signal for rain arriving Tuesday isn’t it?  Every single ensemble member says we turn wet, although not excessively so.  The reason?  The upper-level high that’s over us this weekend:


is replace by a cool trough and a fast westerly jet over the east Pacific.  Here’s next Wednesday.  Quite a bit different isn’t it?


That said, this may not be the big start to the rainy season.  I see all three main model ensembles point to renewed ridging (of some sort) about a week later, on November the 1st.

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So get all your dry-weather activities finished up by Monday afternoon/evening, and enjoy the sunshine this weekend.

Chief Meteorologist Mark Nelsen

A Week of Warm Afternoons & Chilly Nights

October 14, 2018

7pm Sunday…

Weather forecasting is VERY simple this next week.  A strong upper-level ridge of high pressure has moved over the West Coast and should remain in this general position through NEXT weekend.  This is what it looks like today overhead:

Jet Stream Forecast 2017 and next Saturday, not much change is there?

Jet Stream Forecast 2017_a

This is a very stable pattern, especially when I see the same thing on just about all the models and good agreement on the model ensembles themselves.

The east wind showed up, but far weaker than what models were showing Thursday night, the last night I was at work.  They were indicating 6-7 millibars easterly flow through the Gorge or at least from the Columbia Basin to Portland.  Instead it peaked at a paltry 4 mb. this morning.   Crown Point had a gust to 52 mph, weak sauce even for October

Wind Peak Gust Gorge Crown Point

We DID get the downsloping wind today though, dropping dewpoints well down into the 20s for many areas west of the Cascades.  There is one good way you can tell the difference between a regular “Gorge gap wind” and a more unusual downslope wind.  The wind direction with a typical easterly wind event in the cool season is ESE or even SE at PDX.  A downsloping-type wind is E or NE at that location; something I noticed early in my career here.  To summarize the weather pattern the next week?  We’re living in “Central Oregon” right now weatherwise; warm sunny days and cold nights.

This general setup continues through next weekend.  The result will be light frost in spots away from the wind tonight.  The Olympia to Eugene pressure gradient (northerly) is still around 5 millibars this evening which leads me to believe there will be areas of northerly wind at times all night in the Willamette Valley.  That also makes me think frost will be patchy.  We’re going to see some spots (in the breeze) stay in the 40s tonight and calm areas drop to around 30.

Forecast Tonight Metro FOX12PLUS

How much longer will we remain dry?  Models seem to want to break the ridge down early next week (around Tuesday the 23rd), bringing in more typical late October rains at that time.  Check out the rain on most of the ECMWF ensembles suddenly showing up at that time


The top chart shows each of the 51 ensemble members as a horizontal line with accumulating rainfall.  Notice almost all of them produce 1″ or more total rainfall by the 29th.  The average is 2.30″ or so, seen on the bottom chart.  So this EPS shows a very wet pattern for NEXT week.  I noticed the GFS doesn’t seem to want the ridge to disappear through the next two weeks; showing just a bit of a breakdown next week but it doesn’t totally go away.  I’m pretty confident we can forget any chance of a cool & wet pattern through the end of the month, but we may have a mild & wet pattern ahead!

Short-term, offshore (easterly) flow continues through Wednesday, then turns weakly onshore Thursday.  That upper-level ridge rebounding late Friday through Sunday gives us another round of gusty east wind.  Temperatures warm a few degrees tomorrow through Wednesday.  Back off Thursday/Friday with onshore flow, then models are pushing us up to +18 to +19 850mb temps Saturday…that would put us into the upper 70s!

Enjoy the sunshine!

1st East Wind “Event” Of the Season This Weekend

October 11, 2018

9pm Thursday…

You’ve probably noticed; we have entered a remarkable period of mid-October sunshine!  Today was totally sunny except for some spots of brief low clouds and/or fog.  The next 6 days should be mainly cloud-free, or just plain sunny as you can see in our 7 Day Forecast (which you can always find here)

7 Day Forecast Graphic 2017

The reason is a strong upper-level ridge shifting from the eastern Pacific directly over the Pacific Northwest.  It’s going to stick around for quite a long time.  Here’s the forecast from GEFS (GFS ensemble system) for Monday.  Lines are upper-level heights, colors are the anomaly (red = above normal, blue = below).


Then next Wednesday from the EPS (ECMWF ensemble prediction system)


The ridge appears to be strongest at that time.  Looking farther ahead is stretching the limits of weather forecast models, but most interesting is that they all show a similar setup through Day 10…NEXT weekend from the EPS.  Not quite as extreme, but warmer and drier than normal.


So it appears that we are in a long (7-10 day) stretch of unusually dry and warm weather in the Pacific Northwest.

But there is a wrinkle to this forecast…not all of you will be able to enjoy the sunny & warm weather as much because of…the wind.

We’re quickly approaching the cool season (November-March) and that means “East Wind Season” too.  Fall and Spring feature the seasonal oscillation from westerly Gorge wind to easterly wind.  In this case surface high pressure drops down the back side of the upper-level high Saturday through the middle of next week.  Strong high pressure east of the Cascades will give us quite a strong pressure difference across the Cascades.  You can see it on the WRF-GFS surface map for Sunday morning.


That’s 7 millibars easterly gradient from the lower Columbia Basin (near The Dalles) to Portland both Sunday and Monday mornings.  That’s a very strong east wind for October.   Plus, from Saturday afternoon through early Monday it will also be a “downslope” wind.  The layer of easterly flow is deep enough to move right over the Cascades and down into the valleys.

What does that mean for us?

Much of the metro area will be very windy Saturday afternoon through early Monday.  Expect gusts 20-35 mph in the windier spots with gusts at the west end of the Gorge in the 40-55 mph range.  Probably a few scattered power outages as well…under sunny & blue skies.

Of course Crown Point will be a bit stronger…maybe gusts 60-65 mph for the first time this season.  Those highs in the upper 60s will feel quite a bit cooler out there in that wind!

You can see this on the WRF-GFS time/height cross-section over Portland.  Time goes from right to left.  Starting at 5am today (right side) and ending 5pm Sunday on the left.  You see a few 50 kt speeds around 2,500′ over Portland Saturday night and Sunday AM.  That’s impressive even for winter!


The pressure gradient will drop off a bit Tuesday & Wednesday confining wind to the Gorge.  At that point temperatures will likely peak here in Portland as the wind backs off.  We should reach mid-upper 70s on those days.

Enjoy the sunshine Friday and into the weekend, but be ready for things to blow around a bit too!

Chief Meteorologist Mark Nelsen