Strong Wind Spreading Into Willamette Valley

December 14, 2018

1:25pm Friday…

We’ve been expecting gusty wind today and it has been late to arrive.  But in the past hour it has moved from the coastline into the southern Willamette Valley.  Definitely stronger than expected from Corvallis south so far.  Peak gust 44 mph there, 46 at Eugene, and 49 mph at Roseburg.  That’s unusually strong at Roseburg.

A line of showers is spreading into the valley (a cold front) and that will bring those 35-45 mph gusts into Salem and the Portland metro area by 2pm.  Along with that, it’s a warm airmass so we could get up to around 60 degrees briefly right when the wind first arrives.

Of course none of us have “hatches to batten down”, but that saying seems appropriate for the next few hours:  BATTEN DOWN THE HATCHES!

There will of course be some power outages and a tree down here/there.  It’s about time!  A very slow storm season so far.  Here’s the latest view from GOES-17 showing the main frontal cloud band moving onshore.

Capture

Chief Meteorologist Mark Nelsen


Christmas Two Weeks Away…Any Sign of Snow or Ice?

December 11, 2018

7:00pm Tuesday…

A cold front is passing through the eastern side of the Portland metro area at this hour.  That’s a dividing line between a mild airmass and cooler showers beginning to move onshore.  It’s been raining in the Cascades today but that’ll switch to snow by 8pm even in the passes.  I expect 6″ there and up to 12″ by morning up at 6,000′.

MarkWarningsWinterWeather

So tomorrow is your day to head up to the slopes!  It warms up again Thursday and Friday.

Now on to the big question.  Typically I hear a lot of this in mid-December:

“Do you see any snow in our future?”

This is the time of year if you want snow in the lowlands.  Mid-December to early February is “prime-time” in our marginal snow climate.  It’s tough enough to get snow here, but an extra feat to get snow before early December or after Valentine’s Day.  So do we see anything ahead?

At this time there are no signals from any of our models that a cold (or cold/wet) pattern is on the way through at least the next 7-10 days

Snow Portland Preview

Now we can only see details maybe 5-7 days out; beyond time we look for general patterns on our models.  You can find a list of those winter weather patterns on a “tab” above WINTER PATTERNS.  Drew Jackson put these together about 10 years ago.  He’s now in management down at Mt. Bachelor; probably still watching the weather maps closely!

We’ve been in “Pattern B” quite a bit the past few weeks; a splitting jet stream which is common during El Nino winters.  Over the next two weeks I see a bunch of Pattern C (weak Pineapple Express) and D (mild westerly flow) thrown in as well.  If you want lots of snow in the Cascades 2 out of 3 of these are not good.  In fact the ECMWF only gives Government Camp maybe a foot of snow in the next week!  Half of that would be tonight.

ECMWF Snow Accumulation

Now if you want to see heavier Cascade snowfall or snow/cold down into the lowlands you’re going to want to see Pattern “E” or “F”.  There’s absolutely no sign of “E” in the next 8 days or so (cold Gulf of Alaska flow).  And at this point I don’t see the “F” pattern, the one where a big ridge of high pressure develops offshore.  This allows cold arctic air to plunge south into the Pacific Northwest on the back side of that ridge.  Again, no sign of that pattern either.

Let’s take a look at the ECMWF model forecast temps/rain for Portland.

KPDX_2018121112_dx_240

There is no long dry period in the next 10 days, but the only really wet systems pass through right now and again early next week.  Check out those temps!  It’s going to get mild the next 8 days.  Other than Friday morning, we don’t even get close to freezing.  Then you see the drop off in temps around Friday the 21st.  Why the mild temps and lots of rain early/mid next week?  It’s a weak version of a pineapple express as a flat upper-level ridge builds along the West Coast.  It isn’t strong enough to push the rain north of us, but brings very warm air overhead. Here’s the Tuesday forecast.  Strong westerly flow overhead = wet and possibly stormy.

ecm_tues_18th

By late next week we should cool back to normal and that can be seen in the ECMWF meteogram for the next 15 days.  Between the 10-15 day period there is even a hint of a return to a cool & dry pattern like we experienced last week.

KPDX_2018121112_eps_min_max_15

The GEM and GFS models agree with the ECMWF that some sort of upper-level ridging builds again over the Eastern Pacific, relatively close to the West Coast.  See all three forecasts for Christmas Day

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The weather patterns we have experienced these 6 weeks since Halloween have sure screamed El Nino to me.  Splitting, ridging, and a real lack of lower Cascade snow or storminess along the Pacific Northwest coastline…but more on that in a future post.

Chief Meteorologist Mark Nelsen


Gorge Ice/Snow Ending, A Mild Week Ahead

December 9, 2018

8:00pm Sunday

Consider today a “practice run” for a real snow/ice event at some point later this winter.  Thanks to Tracy Hinson for that analogy!

We had a milder/drier version of a Columbia River Gorge Snow/Ice Storm today.

  • Moisture from a cold front moved over the top of a layer of sub-freezing air
  • Strongest wind of the week arrived at the west end of the Gorge.  Strongest wind of the event is usually just before it ends.  Peak gust around 90 mph at Vista House and over 70 at Corbett earlier today.
  • Freezing rain fell at the western end of the Gorge, down to about the 600′ elevation, and that transitioned into ice pellets and then snow farther east in the deeper/colder air.
  • The rain-cooled easterly flow gave Portland its coldest day of the winter so far.  It has been 37 degrees the past 7 hours at PDX!  Brrr…
  • Even the Willamette Valley with the cool northerly flow stayed around 40 or just below most of the day.

This same sequence of events happens time after time, year after year.  What changes is the intensity of the precipitation and the temperature of the airmass flowing from eastern Oregon into western Oregon.  Cold+wetter = ice spreads farther west into the metro area.

This evening the chilly airmass is VERY thin over the metro area and western Gorge.  Troutdale profiler shows “warm” air is only a little over 1,000′ overhead.

Capture

The current view is on the left side; two days ago to the right.  You see the yellow colors (warmer air) working their way down.  Wind is southerly up around 1,800′.

The PDX-DLS pressure gradient has gone from 10 millibars this morning to only 4.2 this hour.  Meanwhile the EUG-OLM (Eugene to Olympia) gradient has gone southerly, about 2.4 millibars.  The weak southerly flow will dominate by sunrise, so NO FREEZING TONIGHT west of the Cascades.

In the Gorge it looks like this:

Gorge Wintry Weather Text 1

After the steady precipitation from the cold front moves east later tonight, there may be areas of clearing from Hood River east; enough to refreeze some wet roads.

Gorge Wintry Weather Text 2

The next 7 days look quite uneventful.  Wet at times, but no cold systems, no storms, but occasional mountain snowfall.  Notice the up and down freezing level.  Avoid skiing Tuesday or Thursday; both those days could be rainy or at least rain/snow mix depending on your elevation.

ECMWF Snow Level From 850mb Temps LONG TERM

The combo of rain, rain/snow, then snow will slowly build up a sorely needed base.  ECMWF says maybe 15-20″ by the time we get to next Sunday.

ECMWF Snow Accumulation

So we don’t have FEET OF SNOW on the way for the Cascades (that’ll be up north in Washington).  Now that all ski areas have at least a few runs open, they should be able to open up a bit more terrain.  There are hints that NEXT week we could see more significant mountain snow; that’s around Sunday the 16th-Wednesday the 19th.

But in this El Nino winter I wouldn’t be surprised to see split-flow return within a couple of weeks.  Regardless, your life can continue as normal for at least the next week, unimpeded by any sort of damaging/crazy weather.

Chief Meteorologist Mark Nelsen


Close to Freezing Rain in Some Valley Spots; But No Icy Roads

December 7, 2018

9:30pm Friday…

A band of rain is moving through the Willamette Valley at this hour, and temperatures are in the 30s for most of us.

web_temperature_ORWA

I see about 3 locations where temperatures are right at freezing; Monroe, Sweet Home, and Eugene areas.  The good news is that dewpoints (measure of moisture in the air) are rising everywhere outside of the Portland “east wind zone”.  The atmosphere is moistening up over the valley and there won’t be any additional cooling (evaporative cooling) tonight.

All the previous points on this morning’s blog post are valid plus:

  1. In the next 2-3 hours trees, decks, tops of cars could get a little ice on them in these coldest spots.
  2. Same thing may happen in the West Hills and other areas above 500′ in the Portland metro area.
  3. NO ROADWAY ICING IS LIKELY ANYWHERE WEST OF THE CASCADES.  IT’S TOO “WARM” IN THE METRO AREA FOR FREEZING RAIN

Temps hold steady or rise a few degrees by morning as we see a bit more rain.

Chief Meteorologist Mark Nelsen

 


Light Freezing Rain/Snow Tonight in Gorge

December 7, 2018

11:00am Friday…

What a chilly night again with temperatures way down in the 20s for most of us.  A strong east wind continues to push cold air westward from east of the Cascades and out into the metro area.  We’ve finally lost the “downslope” wind coming off the Cascades;  that’s why it is much calmer for most of us compared to yesterday morning.  The wind is confined closer to the Gorge.  In the Gorge itself wind will turn quite a bit stronger through late tonight then back off a bit Saturday & Sunday.  That cold east wind will not totally stop blowing until Sunday night.

It’s always nice when our forecast remains consistent; not much has changed in our forecast during the past 36 hours.  Most of the points in the previous post are still valid.   A very weak weather system moves inland this evening, spreading rain into the I-5 corridor (metro area) sometime after 10pm.  It won’t reach the western Gorge until midnight or so.  At that point temperatures will be above freezing in the metro area.  But the airmass in the Gorge has cooled the past two days and freezing rain is likely anywhere from around the Corbett/Cape Horn areas east.

Gorge Wintry Weather Text 1

A big point here is that we don’t have a lot of precipitation coming.  At most 2″ snow could fall in the central Gorge (Cascade Locks & Stevenson) to only a trace out towards Mosier and The Dalles.  Since temperatures are marginally cold, I don’t think it’ll take much for roads to thaw Saturday…a mainly dry day too.

The wetter cold front moving inland Sunday is going to be a bit slow to get here.  Most models are holding off steady rain until at least 10am in the metro area and beyond noon in the Gorge.  That minimizes the areas that should see freezing rain with the heavier precipitation that day.  I feel it’s unlikely I-84 or any other location at river level will see below-freezing temps through the daytime Sunday.  Also, areas west of Bonneville Dam even in the hills will be just above freezing Sunday (Corbett & Cape Horn areas).

Gorge Wintry Weather Text 2

I’ll keep a close eye on conditions through the weekend in case something changes.  Here in the metro area it’ll be a cool one since the easterly flow doesn’t go away until Monday.

Chief Meteorologist Mark Nelsen

 


Gorge Freezing Rain & Snow On The Way This Weekend

December 5, 2018

7pm Wednesday…

It’s been another spectacularly sunny day west of the Cascades under blue sky.  Check out this morning’s GOES-17 image.  If you click on the image (larger view) you can even see Wizard Island in Crater Lake!

Capture

The most important feature for a meteorologist in our area is the large pool of cloud cover below about 4,000′ east of the Cascades.  It fills just about all the Columbia Basin of Eastern Washington and northern Oregon.  That’s the “cold pool” we often talk about in the wintertime.  Cold air is piled up over there.  There is just one little gap through the Cascades where all that chilly air is able to move west of the mountains at sea-level; the Columbia River Gorge.  East wind strengthened today and flowed right over the top of the Cascades too.  The peak gust of 46 mph at PDX around noon was the strongest in a year and a half!  That also gave us our coldest daytime high of this early winter season so far.  That wind strengthens in the Gorge but SHOULD die down a bit in much of the metro area through Friday as a weather system (with its lower pressure) moves toward the coastline.  The return of moisture over the top of cold air in place sets us up for a freezing rain/snow event in the Columbia River Gorge beginning Friday night.

I’ve seen this setup many times.  This isn’t going to be “the big snow/ice storm” out there, but enough to impact your plans if you live east of Troutdale/Camas.

KEY POINTS

  • Cold east wind continues to blow through Sunday night in the western Gorge and east metro area through the weekend
  • Temperatures cool a few more degrees tomorrow & Friday
  • Freezing rain (liquid rain freezing on contact) is likely sometime toward midnight Friday night in the western Gorge (Corbett/Cape Horn to Bonneville). Roads should be very icy within an hour of that rain arrival in those areas.  That may include I-84 assuming temperatures are cold enough at river level.
  • Light snowfall is likely during that time in central/eastern Gorge.  That’s from Cascade Locks to The Dalles in the colder/deeper airmass over there.  Light is the key word, a dusting to 2″ max.  Not a lot of moisture to work with in this first weather system.
  • Saturday is pretty much a dry day…just breezy and chilly again.
  • Heavier freezing rain, possibly some snow eastern Gorge is possible late Saturday night and Sunday.  Could be a significant ice storm in the Central Gorge (Cascade Locks/Stevenson/Hood River) at that time.  I’m not confident it’ll still be cold enough west of Multnomah Falls after a dry day Saturday.  Also some models are holding the moisture off to the west until Sunday morning. We’ll see.
  • The Portland Metro Area will be too “warm” for freezing rain.  But Troutdale/Washougal areas will be very close temperature-wise; a 33-35 degree rain at the coldest point Friday night.

West wind and a general thaw shows up on Monday in the Gorge as a cold front arrives, disrupting the trapped low-level cold airmass eastside and finishing our first “Gorge Event” of the season.

WHY?

  1. COOLING AIRMASS EASTSIDE

The airmass east of the Cascades has cooled the past 24 hours.  By about 3-4 degrees.  More important, the airmass is drier coming through the Gorge.  When precipitation falls into the dry airmass the temperature drops due to evaporative cooling.

The Hood River sounding from WRF-GFS is all below freezing at 4am Saturday = snow in that location, not freezing rain.  Temps are in Celsius along bottom line.

hdrvr.72.0000.snd

EASTERLY FLOW CONTINUES THROUGH WEEKEND

This is a classic setup with a strong surface high pressure stuck east of the Cascades and no low pressure system set to sweep across the region to “knock it down”.  The cool low-level airmass we have in place over us now isn’t going anywhere until Monday.

GOOD MODEL AGREEMENT

The ECMWF and GEM models were first to latch onto a weak system coming in Friday night, then GFS played catch-up.  They all agree the first system has very little moisture to work with but 2nd is wetter.   Notice the light snow by Saturday morning central/eastern Gorge on the WRF-GFS snow forecast.  You can ignore the snow it shows in the western Gorge; the model algorithm paints “snow” anywhere precipitation falls and it’s below freezing under 1,000′ elevation.  But that would be freezing rain in this case.

or_snow72.84.0000

See the 12z ECMWF showing a significant freezing rain event for the western/central Gorge by Sunday PM.

ECMWF Ice Accumulation

It’s only Wednesday evening so some things could still change, but the general sequence of weather events appears to be locked in for this coming weekend.

If you live in the Gorge there isn’t a big snow/ice storm coming but roads could be slippery at times Friday night through Sunday midday.

More tomorrow…

Chief Meteorologist Mark Nelsen

 


A Week of Cold Wind Ahead! Plus Cold Nights

December 3, 2018

6:30pm Monday…

The bright sunshine today was nice wasn’t it?  It always raises my mood this time of year.  In December we “hit bottom” west of the Cascades with respect to the cold season.  It’s our darkest, cloudiest, and typically our coldest month of the year

Of course that is the average.  In some years January is colder (2017).   

Right on cue a very long period of cold east wind has begun this evening.  Why?  A split flow in the jet stream sends a wet system into California this week, keeping us all dry.  There will be no weather systems moving through the Pacific Northwest through at least Friday. 

We have long winter nights this time of year.  The airmass east of the Cascades in the lower elevations loses more heat than it gains during the day; not enough daytime sunshine to overcome the overnight cooling.  The result is strong high pressure centered east of the Cascades through at least next Monday!

There is only one sea level gap through the Cascades and that’s the Columbia River Gorge.  The cool airmass is less than 4,000′ thick so this will be what we call a GAP WIND.  Air will be flowing through this gap.  We don’t get air flowing up and over the mountains in this case (a downslope wind), so only those near the mouth of the Gorge will feel the wind.  That’s the central/east Portland metro area and hills around town too.

Right now the wind is just getting started with gusts around 60 mph at Vista House and 50 in Corbett.  Easterly breezes have begun to show up in the West Hills and east metro too.  Pressure gradients are up to around 4 millibars from The Dalles to Portland.    Models push it to 8 millibars by Tuesday morning and keep it in that general range all the way through next Monday!  This is going to be a long episode of cold wind blasting through the west end of the Gorge as the cold pool deepens east of the mountains. 

Peak gusts will reach 35-50 mph east metro, 60-70 mph western Gorge, and of course 100+ on the Vista House steps either starting tomorrow or Wednesday.

The dry air coming in from the east will minimize morning fog in the metro area tomorrow.  Then eliminate it the rest of the week.  Spots that go calm the next 3-4 nights will be COLD. 

  • Windy areas will likely not drop below 32 all week.
  • Calm areas will be down in the 20-25 degree range each night
  • The coldest outlying areas (Vernonia, Yacolt, etc…) could drop down into the upper teens.

That brings up an interesting point.  This pattern COULD produce the coldest temperature of the winter.  5 of the past 9 winters the coldest temp was in either November or December.  Of course we never know until we get to late February.



Try to stay warm this week and stay out of the wind if you can.

 
Chief Meteorologist Mark Nelsen