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Friday, July 30th, 3:50 P.M. 

Happy Friday!

Clouds and a smoky haze kept today a bit cooler than expected, but it was still very warm with highs making it into the mid 90s around the metro area. We are seeing some showers on the radar, but most of the rain is very light and evaporating before it hits the ground. A chance of thunderstorms or light showers will linger tonight, especially over the Cascades.

Saturday brings more high clouds and a smoky haze above with highs in the low 90s. Expect that smoke to stick around on Sunday, but it should have little to no impact on our air quality.

After a couple more 90 degree days on Monday and Tuesday, things cool off midweek. Thursday and Friday bring our first decent chance of showers in over a month and a half!

  • Posted

7:30pm Sunday...

Well, well...here we are, heading into mid-February and suddenly my app is full of snow. Our FOX12 OREGON app looks like this on my phone

7 to 13" of snow late this week and below freezing temps for at least two days? That would shut the city down wouldn't it?

Notice our "official" 7 day forecast below which is also on the app. Cold temps here too, but no specific snow accumulation forecast. There's good reason for that. As I've mentioned in the past, weather app forecasts are just output from complicated numerical simulations of future weather (the models). No human is touching that app above, but of course we put much more thought into what you see below.

It seems increasingly likely that SOMETHING is in the works along the I-5 corridor for late this week.   Some sort of snow/ice/cold “event” is on the way for some part of the corridor between Seattle and Eugene. Maybe even out to portions of the coastline.

It’s still too far out (4 days) to know how things will play out in detail, but at this point it’s fair to make these statements:

  1. Some, or maybe a large, part of western Oregon and/or western Washington lowlands will get a significant snowfall (2-4″+) within the next 7 days.
  2. The chance for a widespread "arctic freeze" is low right now in our viewing area west of the Cascades. At this point widespread temps below 20 degrees appear unlikely.
  3. A snowstorm is very possible Thursday-Saturday in the Columbia River Gorge, possibly freezing rain too.
  4. Start planning aheadWhat if there is some sort of significant snow/ice event Thursday-Saturday?  How would you deal with it if that’s the case?  It's best to have a plan, even if it all stays up in Western Washington in the end.
  5. There is still plenty of time for this to "fall apart" and nothing happens since it's still 4+ days away. You may remember a year ago (January 2020), a similar "big event" like this was in the forecast. We pulled out of it (#SnowstormCancel) just 2-3 days ahead of time. Nothing happened.
  6. STAY TUNED THIS WEEK AS I'LL BE BLOGGING EACH DAY; AND OF COURSE ON TV EACH EVENING. Follow me on Facebook @marknelsenweather and Twitter @MarkNelsenKPTV for more frequent updates.

At this point, we can't make statements like this until we get closer to the event.

  •  I expect 6-10" snowfall over the Portland metro area Thursday through Saturday morning"
  • Portland will be a frozen hellish white mess Thursday through Sunday
  • 3" will fall over Sheridan but 12" in Molalla"

This graphic summarizes it well

TECHNICAL INFO

There is a lot of cold air just to our north. Most of Montana east of the Rockies is below zero. Very cold in central/northern British Columbia too.

Over the past few days, models have been grappling with how far south to bring that cold air into the Pacific Northwest the latter half of this week. The problem is that we've got two converging flows of air in the upper atmosphere to keep an eye on. Right now up around 18,000'...

Cold arctic air is bottled up generally along the northern arrow. Then a moist and mild flow cutting in to our south. Jump forward to Thursday morning. That southern stream is pushing a bit farther north. One would think it's not an issue right? A bit warmer high up in the atmosphere...mild.

Correct, mild weather likely through Wednesday night or early Thursday IS the forecast. But then look at what's happening down where we live near sea level. An approaching low pressure center from that "southern stream" pulls cold arctic air south through Washington, and through the Columbia River Gorge on Thursday. If this were to happen, temperatures would DROP on Thursday and rain changes over to widespread snow in the metro area and all other points north and east. Remember this is just one model of many.

That IS the perfect setup for a major snow or ice storm for the Portland area. This is the WRF-GFS model, which is based on the USA's GFS model but the ECMWF model is similar. You can see why it's such an issue to make a detailed forecast this far out! Wow, east wind + blowing snow and 20s in Portland, but mild south wind and 40s south of here in the Willamette Valley. Actually there would be an area on the boundary between the two that gets ice pellets and freezing rain. REMEMBER THIS IS ONLY ONE MODEL RUN FROM ONE MODEL. This isn't my forecast.

As always, placement of that surface low approaching the coastline will be critical in determining who gets snow Thursday and early Friday. East wind = cold, south wind = mild. We have lots more information nowadays that can be helpful. Check out this Thursday afternoon forecast from 51 different ECMWF ensemble members. It shows the low center (and depth) for each

  • If the low stays south of ~Tillamook, we get something frozen (snow or freezing rain) in the metro area.
  • If it goes farther north, Portland would only get some brief snow or nothing with a milder south wind. Snowstorm is up in Puget Sound and Chehalis in that case.
  • BUT, if it goes farther south, like several of those lows in the graphic down around Coos Bay? That's a snowstorm all the way from Longview to Eugene. Possibly out along the coastline too!

Hopefully you get the idea...there's far too much up in the air 4 days ahead of time to make an educated guess at this point. In the next two days models will come together and we'll have a better idea. Lots of twists and turns ahead! Plus we'll have to figure out late Friday through early Sunday when ANOTHER LOW approaches the coastline.

I've ignored the extremely cold GEM (Canadian model) for now. It's the only one thinking a lobe of the polar vortex in the upper atmosphere will rotate down over the Pacific Northwest! It would be an all-time cold spell for late winter in that case.

Chief Meteorologist Mark Nelsen

  • Posted

3pm Saturday…

Nothing is more relaxing than a day off work, sitting by the fire, perusing the latest maps/models and meteorological info.  What could be better???  Isn’t that what everyone does?

I’ll be back at work tomorrow, but nowadays everything we need to make forecasts is available online (free or behind a paywall) and can be done from home.  It wasn’t like that 29 years ago when I first began forecasting in Portland.

Today has been a great day for skiing in the mountains.  I see 15-21″ new snow has fallen since Friday morning on Mt. Hood, most of that since sunset Friday.  The problem is high winds.  At 1pm Mt. Hood Meadows closed down after putting lifts on standby for an hour or so.  It’s just too exposed up there in the middle of a storm.  This is a four day long storm folks.  Tomorrow’s wind could be similar as another wave of heavy snow arrives.  By the time the snow tapers off Tuesday morning, we can expect another 3 to 5 feet!  Here’s one snow forecast from a weather forecast model (WRF-GFS) through 4am Monday

wrf_snowthroughMondayAM

We’ve got very large waves on the coastline and some occasional downpours in the lower elevations, but neither is too noteworthy since we’re in the middle of the storm season.

What you really want to know about is lowland snow for next week right?  Now that we’re within 2-5 days of this lowland “snow chance episode”, we’re getting a clearer picture of what’s ahead.

I see two specific periods in which there is a decent chance at least parts of the lowlands west of the Cascades will see sticking snow.  

  1. Monday evening/night
  2. Wednesday (or possibly Wednesday into Thursday)

Notice I didn’t mention tomorrow, tomorrow night, Monday daytime, or Tuesday?  That’s because it’s too warm tomorrow (40s), slightly too warm with strong southwesterly wind Sunday night (snow unlikely to stick much below 1,000′ along I-5 corridor), and a bit too warm Monday (36-40 degree day).  Then Tuesday will likely be dry, or mainly dry and 35-40 degrees too.  That’s why I’m thinking your lives should continue as normal during those times.

MONDAY EVENING/NIGHT

Increasing rain/snow mix Monday afternoon may change to all snow from the metro area south to Eugene around sunset and beyond.  If temps drop down to 32-33 degrees that evening and moisture keeps coming down, this could be a setup for a sloppy 1-3″ snow somewhere between Portland and Eugene.  Everything has to work out just right for this to happen.  So it’s just a chance for now.  But you should be thinking there’s a possibility at least part of this area (including Portland/Salem/Albany) could get sloppy/snowy roads Monday evening/night.  It’s still over two days away so tomorrow we should have a much better idea.  If something fun/snowy is going to happen in the lowlands, this is the first chance.

WEDNESDAY NEXT WEEK

This is our classic setup for a real snow or snow/ice storm.  If enough cold air pours out of the Gorge and into the metro area (and north), we could be left with a snowy/windy/frozen day in Portland.  Of course that extends east into the Gorge as well.  One of those days where most/all schools shutdown and it’s tough to get around.  A real snow day is a possibility.   Models are forecasting a dusting to 6″ (at the high end).  This is why I don’t show snow forecast maps from models many days ahead of time; totally irresponsible and then they get passed around on social media.  Three days ago they were throwing around numbers like 10-20″.  There are strong hints that the cold air may not extend south of the metro area.  It’s quite possible Salem/Albany get little or no snow out of this second event.  And nothing at the coastline.

BEYOND WEDNESDAY

It’s very clear that this week’s flirtation with snow/ice/cold is a one shot deal.  All models swing us back into the mild “split jet stream” setup we’ve seen all winter by next weekend and beyond.   Two of our models have a mild south wind and end of freezing conditions by Thursday morning.

SUMMARY FOR WESTERN LOWLANDS: LONGVIEW TO SALEM INCLUDING PORTLAND

  • SUNDAY EVENING & NIGHT:  Rain showers change to rain/snow showers mixed overnight into Monday morning.  Little or no sticking at lowest elevations and no freezing.  Trace-1″ up around 1,000′.  Maybe a few inches up around 1,500′  Monday morning commute should be perfectly normal, except some snowy roads up around 1,000′ and above.
  • MONDAY DAYTIME: Scattered light rain showers turning to steady afternoon rain.  Mixing w/snow by sunset and possibly changing to all snow and sticking later…beyond 7pm.  Yes, I’ll keep a close eye on this so we can avoid a 2pm, 4pm, 6pm etc… jammed freeway surprise.   Zero to 3″ late Monday evening through the night.  Best chance south of Portland.  Yes, I also realize zero to 3″ sounds ridiculous.  I’ll narrow it down tomorrow afternoon.  Some models keeping all the snow from Salem south at this point.
  • TUESDAY:  Partly cloudy, a flurry or two.  Areas that have snow-covered roads from Monday night would be icy.  But where it doesn’t snow Monday night, both commutes Tuesday will be fine.

METEOROLOGY BEHIND THE FORECAST

This weather pattern is a lot of work, but for a weather geek like me it’s nice to have something interesting ahead.  That’s after 2.5 months of “meteorological melancholy” since Halloween.  I took one day away from the weather maps/models yesterday then jumped back online this morning.  One message sticks out:  The GFS has been terrible leading up to this event, constantly pushing in cold arctic air too fast plus too intense.  I had a feeling that was the case but looking back at maps 2-3 days ago that’s very clear.  Other models have turned a little milder but they were never crazy with the arctic air to start with.  In fact it’s now clear no arctic air moves into the Portland metro area until it gets pulled in through the Gorge Wednesday.  For the geeks this has gone from what could have been an epic event to a typical (somewhat) brief midwinter snow/ice episode with no arctic blast.

That surface low moving by to the north Sunday night gives us far too much onshore flow for lowland sticking snow, even with 850mb temps down around -7/-8, especially since showers appear to dwindle to almost nothing by Monday morning.  I think Monday morning will be a non-event for 95% of us; some grass on some lawns/barkdust here and there but any real snow (1/2″ or more) up around 1,000′ and above. Tuesday’s forecast is easy because the surface low passing through Oregon Monday night is gone.  We’re left with -8/-9 at 850mb and flat gradient.  That should allow us to climb up around 36-40 degrees (assuming ground is bare).  But about that Monday low…

The ECMWF came in this morning going gangbusters with precipitation Monday evening.  It sends the surface low from Florence to La Grande, throwing up around .60″ precipitation over south/east metro!  A light northerly breeze at the same time = possible sticking snow.  The 18z RPM gives us maybe an inch of snow.

RPM_72_SNOW_18z

ECMWF (snowiest) says 2-4″ at least.  This is 12 hour precipitation from 4pm Monday to 4pm Tuesday.  I guarantee this will shift north or south on future runs.

ecm_precipmonday4pm-tuesday4am

Reliable WRF-GFS says band of precip stays mainly south; hosing metro area with little or no snow, but 2-3″ Salem to Eugene.

wrfsnowmonday4pm-Tuesday4pm

As for the 2nd event, both GFS and ECMWF are bringing a very deep low close to the coast, far enough north to put Salem/Albany pretty much out of the running for snow/ice.  Check out the WRF-GFS pressure pattern midday Wednesday…a tad windy in the Gorge maybe?  Strong south wind on the central/south coastline the same time.

wrf_wednesdaypmpressure

That 2nd event is far out in time so I’m sure this will be changing as we get closer.

So remember, the first real chance of lowland snow (for some of us, not all) is Monday evening/night, other than that you’re in the clear.  That’s it for now.

Chief Meteorologist Mark Nelsen