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  • Updated

Sunday, August 1st, 4:15 A.M. 

Good morning!

It’s been tough forecasting over the past couple of days given the cloud cover and some smoke in the sky. On Saturday, the west side of the metro area reached the mid to upper 80s, while the east side was in the upper 70s and low 80s. Clouds & smoke will dictate how warm (or cool) we are over the next couple of afternoons. It doesn’t look like we’ll contend with as much cloud cover today, especially as we head into the afternoon. With increasing sunshine, temps should make a run at 90 degrees. Our atmosphere will warm up a bit between Monday and Tuesday. While we *are* anticipating some thin smoke to be in the sky, we should still manage to climb into the low to mid 90s. Tuesday should be the hottest day, unless if we get some surprise smoke from nearby wildfires. Let’s hope that doesn’t happen.

Between Wednesday and Thursday, high pressure will back off, opening the door to a trough of low pressure dropping out of the Gulf of Alaska. There’s high confidence that a significant cool down is coming, with highs sinking from about 90 to 80 degrees between Wednesday and Thursday. Sometime between Thursday and Friday, showers will likely make a return. This will include much of western Washington and northwest Oregon. As this trough swings through the Northwest, we’ll watch highs dip into the 70s Friday and Saturday. Most signs point to us drying out Saturday & Sunday.

How much rain is on the way? Computer model guidance suggests about a quarter of an inch or less at Portland International Airport. Given we are on a 46 day dry streak and will probably reach 50 days, any rain helps!

Have a great Sunday!

  • Posted

6pm Thursday...

If you haven't left the lowlands this winter, most likely you also haven't seen a single snowflake. February is less than 10 days away! That's unusual in our climate. Typically we have a close call or two, if not real sticking snow, by this point in the winter. Not this year, it's been very mild. But if you are up before 10am Sunday, it appears there's a decent chance you will at least SEE snowflakes in the air. Sledding in the lowlands? Unlikely.

For the short attention span (TLDR) folks...

Winter Weather Highlights

  • Between 4-8am Sunday, precipitation arrives across NW Oregon and SW Washington. Most likely it'll be a rain/snow mix in the lowest elevations (where most of us live)
  • There's a decent chance it falls as mainly snow for at least a few hours 7am-10am, even in the lowest elevations. It could get very exciting weather-wise for a few hours!
  • Temperatures remain ABOVE freezing Saturday night and Sunday = little or no sticking. If it falls heavily enough, it might briefly accumulate on cars/barkdust etc...
  • IF you live up around 1,000' and above, there's a better chance your neighborhood turns totally white for a few hours.
  • IF you live around 1,500' and above, expect 1-3" Sunday morning through midday. There are no spots in the metro area that low.
  • Highways/roads will remain snow-free Sunday in the metro area, except at/above 1,000' where they could briefly turn snow covered.

THIS SHOULD BE A "CONVERSATIONAL SNOW" EVENT FOR THE LOWEST ELEVATIONS. That means everyone will be talking about it; plus posting Instagram/Facebook pictures of their dog/cat/pig/chicken/duck running wildly about outside, but it won't affect our lives otherwise.


TECHNICAL DETAILS

A cool upper-level trough (the first of several) is sliding down north to south along the West Coast. This system is headed for California and far enough offshore that we're seeing almost no showers inland. A mainly dry and cool airmass settles over us Friday & Saturday. Drier air filtering in from Canada gives us LOTS of sunshine Saturday; enjoy that day after a cold start. We're not getting a "cold blast of air" by any means, just a bit colder.

By Saturday night another cold upper-level trough is sliding south along the BC coastline. A cold front then moves inland midday Sunday. Here's a loop from the ECMWF model showing the movement from 1am to 7pm Sunday. Not exactly a "storm" eh? All models have been showing this scenario for several days and all agree on the timing; pretty good for 3-5 days ahead of time.

Freezing levels Sunday morning will be up around 2,000' or so with this system, which typically means we might see snowflakes down to maybe 1,000' and just a rainy Sunday morning in the lowlands. But a few things are different Sunday morning which should bring those flakes lower:

  1. Overnight cooling, while minimal, means this system comes in at the coldest time of day
  2. No significant "warming" onshore wind. There's no cold/dry wind blowing out of the Gorge, but there's no push of warmer air before 10am either. It should be mainly calm Sunday morning, at least for a few hours.
  3. There are signs we get a burst of heavier precipitation between 7-10am. Heavier precip = better chance for flakes to survive a longer fall through the atmosphere

These all point to a setup where snowflakes may survive falling all the way down to the valley floors west of the Cascades (less likely along the coastline) for a few hours Sunday morning. The reliable WRF-GFS model from UW shows the above freezing temps through Saturday night. At 4am the forecast sounding shows it's in the mid-upper 30s in Portland. This isn't a setup where precipitation arrives at sunrise after a frozen night.

But as precipitation starts falling, look how surface temp drops to 33-36 degree range around 7am

Then 10am

That's pretty much a snow sounding; at/below freezing except for the lowest 500' or so. By 1pm Sunday, the cold front has passed, mixing (warming) the lowest layer of the atmosphere with a southwest or westerly wind. At that point we'll just see rain or mixed rain/snow showers. It appears we have .25 to .50" precipitation to work with, enough for 1-3" in higher elevations where this falls as snow and sticks.

Models ALWAYS struggle with predicting snow totals in these marginal events. This morning's ECMWF model continues the "little or no sticking snow" idea; you need to be up/above 1,000' (or 1,500') to make a snowman this time around

Note the coarse resolution here. I've purposely left it "unsmoothed" so you can see the model resolution. It doesn't see the West Hills or Chehalem Mtn. at this 9 kilometer resolution. It also doesn't "see" the Columbia River gap between Woodland and Longview, thus painting a bunch of snow for Kalama, Rainier, Longview, & St. Helens. It "thinks" the hills of Columbia county OR just merge into the hills above Kalama & Woodland. Higher resolution models (4km & lower) DO show those features, but we don't have those today. They run just 72 hours out in time and only cover to 4am Sunday.

Alright, so that's your first "big snow chance" for this season. That was a joke, it's not a big snow chance. We MIGHT be close again early next week (either Monday morning or Tuesday night), but we can discuss later.

I still want to be clear that this is the not the beginning of a cold/snowy weather pattern. Sure, we'll be getting more regular frost and overnight freezing. But no sign of an arctic blast through at least the first few days of February.

I probably won't post tomorrow considering how minor this event will be; time to get out and enjoy the wintry outdoors. I'll definitely be back with an update Saturday.

  • Posted

8:45pm Wednesday…

Today turned out pretty much as expected, with a few last minute twists & turns.

  1. We saw a rain/snow mix which changed to mainly rain as the cold front moved through during the evening commute
  2. Clark county warmed up to around 40 as our “mesoscale” models showed; no snow for most of you up there.
  3. No measurable snow for almost all of us.

What was different than expected?

  1. Cold Gorge wind was very persistent (surprise!).  Although quite a bit more reasonable compared to a few hours ago, it is still transporting cold continental air westward into the eastern edges of the metro area.  Temperatures are hovering just above freezing in a narrow area along the Columbia River east of I-205
  2. Due to that, plus the cooling air overhead, snow has been falling for several hours in the western Gorge, all the way into Camas and Washougal.  Just got a report that two inches have fallen in Bridal Veil, that’s where we should have only seen freezing rain.

Take a look at current temps, only the numbers below 34 degrees plotted below. (click for a better view)

Capture

Areas to the right of the yellow line are generally seeing snow.  Mainly or all rain to the left.  Yet in general the snow level west of the Cascades is around 1,500 to 2,000′ right now.  Then how is it snowing down to the Columbia River in Clark and Multnomah counties?  What would typically be about a 1,500′ snow level right near the Gorge and into Camas/Washougal has become “sea level snow” since the last 1,000′ or so are near/below freezing due to that east wind; snowflakes are coming down much lower than one would expect in this pattern.   Due to this, and more precipitation on the way, the NWS has upgraded the western & central Columbia River Gorge to a Winter Storm Warning.  3-6″ likely in these areas.  The pressure difference through the Gorge does continue to weaken and it’s possible at some point Camas/Washougal/Troutdale lose the easterly wind.  If so temps will rise a few degrees.  They sure won’t go down any lower through tomorrow morning.

Mark Gorge Wintry Weather

Through the rest of tonight we’ll see waves of showers moving onshore behind this evening’s cold front.  In general the snow level will remain above 1,000′ through tomorrow morning.  But anyone at/above that elevation in the metro area could see a skiff of snow on the lawn/barkdust/car.  Same setup again tomorrow night and Friday morning.  Beyond that time we’re headed back to a milder weather pattern for the last 1/3 of January.

Chief Meteorologist Mark Nelsen

  • Posted

8pm Sunday…

Here we are, finally at the end of Christmas Vacation for the kids.  It’s been a fun two weeks for many of us; full of family events, parties, and WAY too much eating and…drinks.  Time to get back to work and school.  First, a quick recap of where we stand meteorologically:

  • We are at the midpoint of our  “cold season/winter/storm season” (whatever you want to call it) west of the Cascades.  That’s November through February.  By March 1st we’re done with winter west of the Cascades unless we get a sloppy/wet brief snowfall.  Last year’s early March record cold & snow would be an extreme example of how winter can hang on very late here every few decades.
  • It’s been so boring for meteorologists with a lack of stormy weather, lowland snow/ice, etc… But great for you!  Weather has barely affected our lives so far, except for the brief snowy travel issues at Thanksgiving and lack of snow in Cascades.  Officially we have not seen measurable snow in Portland.

Now we seem to be turning a corner, at least for the next 10 days.  We’re now in a cooler & wetter weather pattern; back to normal!

Highlights

  1. Expect at least SOME rain each of the next 7 days as a series of relatively weak weather systems move off the Pacific and into the Northwest.
  2. None of these systems look particularly strong, windy, or cold.  But each will add to our January rain total in the lowlands and snowpack in the Cascades
  3. Snow levels vary between 1,500′ & 5,000′ through Saturday
  4. Models are hinting that snow could stick even lower at some point between next Sunday and the days following (12th-15th).  Some produce NO snow, others give us a big outbreak of cold arctic air and several inches.
  5. That period will likely feature the lowest snow levels since our brush with lowland snow Thanksgiving weekend.  I’ve put on my snow tires (finally) just in case…

Expect 2 to 5 feet of snow in the Cascades now through next Sunday. Here’s the ECMWF model (Euro).  Can’t wait to see that 25% of normal snowfall on Mt. Hood jump up big-time the next 10 days!

ECMWF Snow Accumulation

What I don’t see within the next week (through Sunday the 12th)

  • Sticking snow at lowest elevations west of the Cascades OR along I-84 in the Gorge
  • Freezing Rain
  • Flooding
  • A Windstorm
  • A Hard Freeze (below 28 degrees west of Cascades)

We’re in a wet westerly flow right now with a nice Pacific jet stream aimed at the West Coast.  Here’s the ECMWF ensemble forecast 500 millibar height map right now:

euro now

But by next Monday, ALL models agree we’re in a pattern with an upper-level high out around 150-160W longitude (south of Alaska) and a cold trough centered over the western USA.  This is the ECMWF for next Monday

euro ensemble monday 14th

The Canadian and GFS are similar.  Click on each for a larger view.

So that’s relatively simple…cooler (or colder) and still a bit wet 8 days from now.  But in our climate, with hundreds of miles of 50 degree water just to our west, everything has to work just right to get us real cold or snow all the way down to sea level.  So all models may agree on the general pattern by next Monday, but how we get to that point and exactly how all the weather features line up is critical.  Slight changes mean the difference between a hellish snowy commute at some point in Portland, or just 40 degree rainy weather.

Example A:  For several days the (new and improved) GFS model has been constantly trying to dig weather systems farther west out of Canada as they move southeast into the cool trough across the western USA.  That’s for this coming Saturday, Sunday, or Monday.  It has been most aggressive bringing cold arctic air south into the Pacific Northwest.  Today’s 18z model was very extreme, going all out for widespread snow in our area with a cold east wind Sunday night.  See the arctic boundary (snow to sea level) way down into Oregon on that model (yellow highlighting)

gfs18zSunday evening

The GEM at the same time has a surface low sliding into NW Washington, keeping cold air bottled up north.  On Sunday evening the GEM would say it’s 40 degrees with a gusty south wind blowing in Portland…totally different even though upper-level is similar.  It’s all about low/high pressure locations for us.

gem12zSunday evening

The ECMWF?  It says “mainly dry” with the arctic boundary up north and a weaker low heading farther south.  This says snow showers to 1,500′ and nothing interesting happening in Portland Sunday evening.

ecm12zSunday evening

To summarize:

  1. I think SOMETHING interesting is on the way NEXT week, but it’s too early to know what.  Too early to know if it involves lowland snow/ice/cold or just a brush with flurries again like Thanksgiving.
  2. Keep a close eye on forecasts, this blog, and on-air at FOX12 OREGON.
  3. As a nod to the GFS, I put one little lonely snowflake mixed in with the rain on our 7 Day Forecast (next Sunday)
  4. And, for the love of any sort of deity…stop staring at weather apps!  They are good for general weather forecasting during benign weather, but useless in situations like this.  Totally automated.  Plus, what does a snowflake for next Monday mean; a snowy day? a few flurries?

Weather App Snow Forecasts

Chief Meteorologist Mark Nelsen

  • Posted

It’s been another COLD day (for early March) across much of the Pacific Northwest. It’s not really all that cold west of the Cascades but eastside is a different story.  Check out those HIGH temperatures right around 20 in Central Oregon and Pendleton.

Todays Observed Highs OrWa 2017

The Dalles has never been this cold in March, reaching below 10 degrees this morning.

Cold Temps Record Eastern Oregon March

This morning in the metro area some of us made it down into the upper teens.  Not too unusual in December or January, but I’ve never seen it this cold in early March.  Still, it’s been 30 years since that cold March 1989 start so it was probably time to get a cold spell.

We have a VERY dry airmass over our region right now, dewpoints have been around 10 degrees here in Portland.  When you bring that dry air indoors and heat it up to 70, you get a relative humidity around 10%.  That explains a dry throat, skin, and possibly a blood nose too!

So you’ve probably noticed some snowflakes on your weather app again.  What’s up?

All models show moisture in the form of clouds and then precipitation moving north out of California Tuesday night and Wednesday morning.  This rides over the cold airmass already in place over us.  The result could look something like this during the Wednesday morning commute:

RPM Clouds Rain Snow

Light snow falling with temperatures right around freezing.  In early March everything has to be just right for snow to stick to lower elevations.  This appears to be a rare case when that could happen.  BUT, each model is different and some are too dry or too warm.

For example the ECMWF shows very little snow accumulation through Wednesday afternoon, but then tries to put down some light snow in the Portland area Wednesday evening/night.  Not sure if I buy that at this point.

ECMWF Snow Accumulation

The brand new evening GEM model wants to put an inch of snow over the metro area between 11am and 4pm Wednesday; extremely unlikely during the middle of the day plus its own temperatures are 35-38 during the time it’s generating sticking snow

GEM Snow Accumulation

 

SUMMARY

  • At this point I don’t see a snowy/hellish commute Wednesday morning.  But be aware it’s a POSSIBILITY that somewhere in the lower elevations there could be at least a dusting of snow on the ground (or roads) at that time.
  • Whatever happens Wednesday morning, most likely it’ll just transition to rain/snow mixed the rest of the day as slightly milder air moves in.
  • Wednesday night and Thursday morning snow levels remain low, but most likely we’re talking brief morning rain/snow mix and sticking mainly in hills.
  • The cold/dry weather and the gusty east wind will be gone after Wednesday morning.  We’re headed into a “cold showers with sloppy snow in the hills” sort of weather pattern Wednesday PM through Friday.

After the morning models come in tomorrow I’ll put up a more detailed blog post.