Colder & Drier Next 7-10 Days

November 18, 2015

11pm Wednesday…This first half of November has been extremely wet to the north and west of the Portland metro area.  Here in Portland precipitation has been about average and a bit below normal (so far) in southern Oregon.

MarkRain_NW_TotalsThose Washington and coastal rain totals have been amazing.  11″ at Olympia just a little past halfway through the month…

But things are about to change…I think splitting systems and upper-level ridging nearby will be the dominant theme for the next 10 days.

Next week (Thanksgiving Week!) ridging to our northwest will allow a surge of colder air to slip south.  That happens Tuesday and Wednesday.  Models earlier today were VERY cold, and I didn’t jump on that right away.  This evenings runs of the GEM, ECMWF, & GFS are a bit more reasonable with a very chilly, but mainly dry pattern most of next week.  You get the general picture here:


Is it cold enough that we could see snow?  Possible, but as of now I’d lean towards scattered showers Tuesday and/or early Wednesday and then just turning mainly sunny and cool heading into Thanksgiving.  That’s definitely subject to change since we’re talking about something 6-7 days away, thus the reason I’m not all excited about it yet.

By the way, the 15 day ensemble charts from the GEM/GFS/ECMWF all show the ridging developing early next week hangs around for the next two weeks, but flopping more right over us or just north.  Here are the 500mb height anomaly maps for around December 3rd…two weeks from now.  Click on each for a larger view:

The good news is that the weekend looks really nice with abundant sunshine, comfortable days, and chilly nights!  We should see the most widespread frost so far over the weekend.

Chief Meteorologist Mark Nelsen


Windstorm Wrap & Possible Gorge Snow Tonight

November 18, 2015

9am Wednesday…

I had two days off and flew back into PDX around 4pm yesterday…a bit bumpy!  A huge change to go from warm and sunny southern California to pouring/sideways rain on the way home.  Then 30 minutes after I got home the power went off for the next 5 hours.  My wife didn’t seem to appreciate it when I remarked something like “this great!  Better than coming home to boring 45 degrees and cloudy…”.  She just doesn’t share the weather geekery!


Tuesday’s windstorm was a rare event in the western/central Columbia River Gorge and then out into the Columbia Basin.  The 69 mph gust (near ground level) at Bonneville Dam was the strongest wind I’ve seen at that location.  In fact I can’t remember a damaging westerly wind event in the past 20 years in that area.  Even the sensor at Vista House, all of 18″ out from the stone wall, somehow recorded a gust to 48 mph (direction is broken) from the southwest.  Biddle Butte, at 1,400′ above Cape Horn, had a gust to 59 mph.  I haven’t seen that the past few years either.  Due to those strong winds lots of trees fell across or near I-84 so the freeway has been closed for about 12 hours eastbound.

In Eastern Washington it gusted to 71 mph at Spokane; more damage/outages in that metro area than the 1996 ice storm.  I also saw reference to that gust being the strongest non-thunderstorm wind gust on record for them.  Don’t know if that’s true or not.  But a huge windstorm for the Inland Northwest.

Of course for much of the Portland Metro area the wind wasn’t anything out of the ordinary for November, lots of gusts 30-40 mph, barely even worth of a wind advisory.  This was a Gorge and East of the Cascades event.

11_17_PeakMetroGustsPDX actually gusted to 43 mph; the 40 was a mistake.  Note the Troutdale profiler (in place for research this winter and next) shows 60-70 mph wind just 1,500-2000′ above the surface


The pressure gradients were amazing for this event.  17 millibars from Eugene to Olympia shows the potential was there for much stronger wind in the metro area.  A typical guess for south wind in our area is 3.2 X EUG-OLM gradient.  That gives gusts 50-60 mph in our area.  We underachieved a bit.  And 27 millibars from North Bend (OR) to Spokane!  About the highest I’ve seen.

Models showed a very tight gradient ahead of the cold front, maybe a little weaker than what actually showed up westside and definitely underdone a bit in Eastern Washington.  Here’s the 4pm forecast from yesterday morning’s WRF-GFS:


I checked the 4/3 km high-res run for the western/central Gorge and that didn’t capture the big surge of wind.  We still have some things to learn!



We have a weak system moving through the area tonight on a totally different track.  No dramatic rain/wind issues with this one, because it’s a weak surface low coming right across the central Willamette Valley.  The bulk of the rain/snow is headed south of the Columbia River…maybe .50-.75″ of rain overnight total in the metro area, then drying quickly Thursday.

There is one interesting part; with the surface low approaching wind turns easterly in the Gorge and light easterly in the metro area.  That means snow will fall to relatively low elevations in the central/eastern Gorge.  Note the morning WRF sounding for Hood River at 7am Thursday:


Expect 1-3″ snow up around 500-1,000′ in the central/eastern Gorge overnight.  Just rain at the west end.  It could even be white for the first time this season down in Hood River by sunrise.  Winter is getting closer!

Chief Meteorologist Mark Nelsen




A Weekend Break

November 13, 2015

I will be “offline” through Tuesday afternoon taking a long weekend, so no blog posts.  That said, I think I can summarize the forecast anyway:

Rainy, then cooler & showery, then rainy and warmer.  That covers the next 4 days pretty well.  Right now this is what I’m thinking for Cascade snow:


Unless the Monday snow fails to materialize, I think this could be enough to open the bunny slopes and maybe one more lift at Meadows and Timberline next weekend…we’ll see.

Chief Meteorologist Mark Nelsen

Saturday Forecast Looks Drier Here: But Heavy Rain Up North

November 12, 2015

9pm Thursday…

An interesting turn of events for this weekend; all models are keeping just about all rain out of the Willamette Valley and Clark County through Saturday afternoon.  I’m REALLY glad I didn’t make a big deal out of Saturday’s rain…whew!  It will eventually rain Saturday evening, but nothing too unusual.  Here’s the rain forecast for the next 48 hours from the evening UW-WRF model:


and the evening NAM-MM5 from the UW:


Not much rain through Saturday afternoon here…

Why the change?  It’s somewhat related to my weekend plans; I have a long weekend planned in Southern California.  Over the last few days I’ve been watching the maps for down there pretty closely and each day models have been digging our system farther and farther south.  At one point it looked like 80 degrees where I’m heading Monday and Tuesday.  Not it looks to be around 65.  The point is the southern part of this system is showing more and more energy and now we see that stalls the northern portion late Friday-Saturday.  The weak split can be seen in the 500mb chart for Saturday afternoon:


This may (or may not) be the beginning of a splitty winter pattern we would expect in a strong El Nino year.  We’ve seen this happen a few times in the past few weeks (the splitting) and it really shows up again on tonight’s GFS run.  That said, it IS the GFS…

A surface low even develops off the southern Oregon coast with this splitting.  As a result, rain totals by Sunday afternoon look very heavy from around the mouth of the Columbia River up into SW Washington north of Longview.  Watch out on the Chehalis River!  The Portland NWS has just issued a Flood Watch for that area in yellow.


Note nothing too excessive south of the Columbia inland…maybe an inch or so in Portland.

For skiers, the good news is the snow changing to rain right now will let up and it’ll be mainly dry up there through Saturday.  Then a decent dump Saturday night and Sunday.  I’m thinking 6-10″ is likely at Government Camp by Monday morning.  Higher up additional snow will fall Monday before snow levels take a huge jump Tuesday.

Looking farther ahead models are a bit of a mess.  ECMWF and earlier runs of the GFS were very wet Tuesday-Wednesday with a ton of snow in the Cascades Wednesday.  This evening’s GFS has much more ridging and casts doubt on that snow forecast…we’ll see.

And a sure sign winter is almost here!

The 18z GFS gave us the first model forecast of an arctic blast.  There will be many more teases like this through February.  It showed a massive plunge of cold air (some snow to sea level too) the day before Thanksgiving.  Temps probably 25 degrees in the metro area on Thanksgiving Day for a high.  But, the next run has nothing of the sort…easy come, easy go!  Time to get your tickets and board the WishCast Express…


Very Dramatic Weather Headlines This Week

November 11, 2015

For the 2nd time this week I’ve seen a very dramatic headline on the top banner of a well-known local newspaper website:


The first was


and, for the 2nd time this week I think it’s pretty unlikely.

By the way, the Mt. Hood area picked up around 1-6″ snow out of that system the past 24 hours.  Models at that time were showing maybe 6-10″ max around Mt. Hood when the first headline came out.  Not sure what’s going on and how these headlines are showing up, but it appears a newspaper can actually top a TV newscast for hype!  That’s a new one.

So what’s really going on?

For the next two days a steady stream of moisture, a firehose-like atmospheric river, will be running into mainly the northern half of Washington.  That leaves us with just a few light showers through Friday night here in most of northern Oregon.

Then late Friday night and Saturday a cold front with its heavy rain band moves down through Oregon.  We definitely get a soaking, but not insanely wet like Halloween.  We saw rainfall rates of 1-1.5″ in just 2-3 hours with that storm. This time we’re talking maybe 1″ in 6 hours…like our RPM shows below.  Note the highlighted total during the day Saturday.


An inch in 6 hours is a steady/heavy winter rain around here.  That’s wet!  But urban storm drains can handle .30″/hour just fine.

The latest GFS model is a bit less intense, about .70″ in those 6 hours ending at 4pm Sunday.


The latest ECMWF model was similar to this…a very wet day, but nothing we don’t typically see in November.  Each model is a bit different and I’ve seen two models in the past 24 hours are a bit heavier.  Our evening RPM model run shows 1-1.50″ in the metro area, and far less in the mountains compared to what fell 2 weeks ago:


So to recap, as of 8pm Wednesday evening:


Chief Meteorologist Mark Nelsen

Cascade Snow Update

November 10, 2015


Today was sure a chilly one across the area…the coldest day since February 1st in Portland.  In fact every other day in February was warmer than today; that shows you how freakishly warm February was!


There is a cold front just offshore that is approaching this evening.  We’ll see a quick burst of rain in the valleys and snow in the Cascades overnight and early Wednesday morning.  The weekend “snowy” system in the Cascades definitely underperformed and we hope that doesn’t happen again this time around.  Here’s a look at what I’m looking for in the upcoming week around Mt. Hood.  2-6″ range for tonight is from 4,000′ on up to 6,000′.  This should be the first time we actually see roads turn white around Government Camp this season…later than normal.


Beyond that Veteran’s Day looks more dry than wet to me and Thursday will be dry.  We have a warm and wet atmospheric-river type event coming up for Washington Friday and possibly part of Saturday.  We are on the southern edge of that so current rain forecasts through Friday evening are very light overhead…much like what we saw the Friday/Saturday around Halloween.


What I don’t expect (as of now) is a repeat of the huge downpours on Saturday.  The latest GFS is moving the cold front through here very quickly Saturday morning which would keep any flood issues in check.  The 18z had extremely heavy rain over us…maybe 2-3″ from 7am-7pm!  We’ll hope that solution doesn’t return.

Friday and Saturday we’ll see snow levels way too high for snow in the Cascades, but then much colder air arrives Sunday and Monday.  As you can see on the graphic above, that should mean more snow for the ski areas.

There are indications we go into a drier pattern about 10 days out on both the GFS and ECMWF.  With this upcoming snow ahead of that time MAYBE, just maybe, we’ll see some ski areas attempt an opening the weekend before Thanksgiving…that would be the 21st/22nd.

Chief Meteorologist Mark Nelsen

Looking Good For Snow In Cascades!

November 6, 2015

11pm Friday…

Every November we start the month wondering how the ski season will commence:

  • Will it be a series of cold storms that give us 3-4 feet of snow in a week that quickly opens a bunch of ski areas?


  • Will it be one of those starts that just sort of limps along with only a couple of ski areas open through early December?

Right not it appears we COULD be looking at something closer to the first option.  The pattern over the next 10-14 days looks pretty cool (most of the time) to me.  FIrst take a look at the next 7 Days…not any huge storms but maybe a foot on the ground above 5,000′ by Thursday morning:


It’s pretty obvious looking at models that the snow on the ground at/above 6,000′ isn’t going anywhere either.  Check out the 12z ECMWF ensemble chart…


I know, lots of lines.  This is temperature in celsius at the 5,000′ elevation.  The green line is average over the next 15 days.  The thick blue line is the operational run we all look at.  Each little black line is one member of the 51 member ensemble prediction system.  The red line is the average of all the ensembles.  Note that most of the next 10 days the temperature is below normal.  It’s briefly warm next Thursday/Friday, but then turns cold again NEXT weekend.  The GFS model shows a lot of precipitation starting next Wednesday.  2-3″ from that point through day 10 over Portland and much more over the mountains:


For snow, it shows maybe 20-25″ on Mt. Hood (around 5,000′ or so) in the next 10 days:


The brand new 00z ECMWF doesn’t have quite as much rain/snow but the pattern is the same.

So this MAY be the year we see some openings at least a week before Thanksgiving, at least just a few lifts to get things going.  The good news is that there is no sign of dry ridging like what we saw back in January/February last winter.

Chief Meteorologist Mark Nelsen


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