No Skiing/Snowboarding Yet, But No Need To Panic

9:30pm Tuesday…

Thanksgiving has come and gone, along with all that snow that fell last week in the Cascades. About a week ago the snow was between 6-18″ deep at the Mt. Hood ski resorts. But that is all gone now. Here’s the view at Mt. Hood Meadows base area yesterday morning; most of those patches are now gone.

And way up at 6,000′ at Mt. Bachelor’s base area

Having mainly bare slopes at these elevations IS unusual as we head into the first few days of December, yet not unheard of. Check out snow depth on November 29th each year at the SNOTEL site in Timberline’s ski area

It’s the lowest since 2008. In fact I still have the picture from a blog post on December 1st, 2008

What happened later that year? Well, it looked like this on December 23rd at my home near Corbett

Yep, a cold wave arrived around mid-month and snow started accumulating not only in the Cascades but down in the valleys as well. The Mt. Hood Test Site (SNOTEL) went from just about nothing in early December to just under 9 FEET of snow on the ground by New Year’s Day! Over 500″ fell that winter. Proof that things can change quickly this time of year. Mt. Hood Meadows put out a nice “scatter plot” graphic today. The image below shows how much snowfall they get each season vs. opening date. An average winter picks up around 450″ at that 5,400′ elevation. There DOES seem to be a tendency for lower seasonal totals with later starts, but not dramatic most years.

It appears that only 5 of the past 26 seasons have started this late (sometime beyond December 5th). 3 of those ended up with reasonable conditions, two not so much.

What’s ahead?

The reason it’s been so mild has been stronger than normal upper-level ridging over the West Coast. That’s sending lots of warm-ish storms inland just to our north (NW Washington flooding). That general pattern continues for at least another 7 days. Our 7 day forecast for Government Camp says no chance for skiing through at least the 8th of the month

This chart shows the 850 millibar temperature forecast for the next 16 days…from the European model. That’s temperature in Celsius around pass elevation around Mt. Hood. The green line shows the ensemble average, and I’ve put a yellow highlight at “0”. Anytime temperatures are near/below that line precipitation would generally fall as snow in the Cascades. Notice there is a change just beyond our 7 day forecast. IN GENERAL, models are expecting cooler conditions from that point forward, and they’ve been hinting at that general change for the past 1-2 weeks.

Other models are similar, so to summarize:

1. This extremely low early December snow depth is unusual, but it has happened in the past
2. There’s no reason (at this point) to believe this means a poor ski season or low snow year in the Cascades
3. There’s good reason to believe we will see a pattern change, kicking the ski season into gear, about 7-10 days from now…maybe some skiing for the 2nd weekend of December!
4. Don’t panic! Be patient…

Chief Meteorologist Mark Nelsen

Mild Weather & (Mostly) Good Travel For Thanksgiving Week

8pm Monday…

Most likely you experienced a mainly sunny weekend, OR a foggy/cloudy one. It all depends on your location because we saw the first seasonal “inversion” across the region. That’s when cool overnight air stays trapped in the valleys during the very long “winter” nights, along with moisture. The combo leads to persistent fog/clouds in some valley locations both east and west of the Cascades and it happened over the weekend, especially Sunday. This is a common feature of our climate from late November through late February.

Portland only made it to 46 yesterday and parts of the valley never broke out of the gray. Meanwhile east metro areas stayed clear with just enough drier Gorge wind keeping the clouds away. The Cascades remained sunny above the inversions too. In fact Central Oregon (above 2,000′) popped into the 60s today!

A cold front is approaching tonight and that’ll bring us with the usual steady rain turning to showers. This time a much colder airmass follows, along with strong WESTERLY flow into the Cascades. That should be very efficient at dumping lots of snow up there. 6-10″ is likely, on top of the 2-6″ on the ground at the ski resorts.

Of course that isn’t enough for Thanksgiving Weekend skiing, especially with the snow level headed WAY up the rest of the week. Lots of mild weather to wrap up November…

This mild weather pattern is caused by a “flat” upper-level ridge in the atmosphere; that’s warmer than average air over the western USA. Here’s the 500mb map for Thanksgiving Day

And then again NEXT Monday, the 29th…still mild

By the way, there are strong hints from our long range models that a turn toward more typical or even colder than normal December weather might show up about two weeks from now, but that’s WAY out there…

For now, expect lots of days in the 50s over the next week with little/no weather impacts on your Thanksgiving travel. I’ve covered the Cascades…snowy tomorrow through Wednesday morning, then much better Wednesday afternoon and pretty much clear through passes Thursday. How about the Gorge? No sign of cold air, but tomorrow’s snow WILL impact the Blue Mountains between Pendleton and La Grande

Coast Range passes will be all clear through the weekend, as will I-5 both north and south of us. Sometimes we see snow at I-5’s Siskiyou Summit south of Ashland this early in the season, but nothing significant is in the works for this long weekend.

That’s it for now, enjoy the mild Thanksgiving holiday!

Chief Meteorologist Mark Nelsen

Late November Weather Slowdown In Pacific Northwest

7pm Tuesday…

The first half of November has been very warm in the Pacific Northwest, 3rd warmest on record (first half of month) at PDX.

Now that’s partially due to a long-lived atmospheric river event late last week through Monday. That was a real doozy in Washington, not as extreme in Oregon. Huge rain totals with record flooding the past few days in SW British Columbia and NW Washington. Portland picked up just under 3″ out of the event Thursday-Friday, an excellent forecast by forecast models.

Then a strong cold front finished things off yesterday with a gusty south wind that quickly switched to northwest in the afternoon. Peak gusts were in the 25-40 mph range for most of us, the 4th time PDX has seen a gust at/higher than 40 mph this season. Lots of moderate wind, but no windstorm in the valleys yet this season. Mental reminder: The HRRR model tends to over-forecast wind gusts, it’s been too high most of the time this season. Our GRAF model has done very well.

Rain is running well ahead of average for November…just over another 1/2″ will send PDX over the typical monthly allotment. But now the weather is slowing down dramatically.

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WHAT’S AHEAD?

Much calmer weather which shouldn’t affect your day to day living…

Through at least Thanksgiving Day I don’t see:

1. A storm of any sort west of the Cascades
2. Lowland cold and/or snow
3. A big snowfall to jump start the ski season

In general, upper-level heights will be a bit higher than normal along/off the West Coast. That has not been the case most of the time in the past month. This chart shows 500 millibar height (around 18,000′ overhead) averaged over the next ten days…the lines. Warm colors represent highs higher (warmer) than normal

That leads to less precipitation than normal…both the GFS and ECMWF ensembles are similar (GFS here). Not DRY, but DRIER THAN AVERAGE for this time of year.

Just beyond that time (later Thanksgiving Weekend and beyond) models diverge. At this point GFS ensemble members are bringing in a wet southwesterly flow again, but ECMWF & Canadian models think ridging moves overhead for drier than normal conditions through the end of November. We will see, that’s pretty far out. Regardless, I only see two rainy periods in the next week. That’s later Thursday through Friday, then again Monday (very light). These will be relatively weak systems, not significant wind producers. I love this chart…it shows all 51 ECMWF ensemble members for the next two weeks. Each square represents a forecast 6 hour maximum gust in Portland. The lowest part of the chart shows the average of all 51 members. With just a quick glance I can see where windy periods may show up, plus any real “outliers”. That refers to numbers much higher than others.

Gusty easterly wind tomorrow through Thursday morning shows up well on all ensemble members. Most interesting is that there isn’t a single ensemble member trying for a 50 mph gust in the next 16 days! Of course that doesn’t mean we don’t have a storm coming sometime beyond the next 7 days, but in general we don’t see a stormy period ahead.

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SKI AREA OPENINGS

Last week things were looking up with 10-15″ fresh snow on the ground at the ski resorts. We were just a storm or two away from at least a few runs opening up on Mt. Hood. Then 5-6″ rain fell on that snow and warm/humid weather melted all of it! Cold showers last night dropped 2-5″ snow on those resorts. It appears only a dusting is on the ground down at Mt. Bachelor west of Bend. This is not unusual for mid-November as you see, but skiers/snowboarders just remember the big starts. 2017 and last year we had some nice snow on the ground at this point.

What’s ahead?

We sure don’t want to see those higher than normal upper-level heights over the next week as I mentioned earlier in the post. That means weak systems and a bit warmer than normal. So very little accumulation at the resorts at least through next Wednesday.

BUT, things can change quickly this time of year. Stay tuned to see if we get that cooler/wetter pattern as we go through Thanksgiving Weekend.

Chief Meteorologist Mark Nelsen

Pineapple Express Is Here! More Rain Ahead But Mainly Dry Weekend

6pm Thursday…

Now THIS is the November weather I remember growing up with west of the Cascades…day after day of rain and mild weather. Some southerly breezes, then a bit of mountain snow. Annoying if you want to get outside, but great to see the ground saturating, reservoirs refilling, and (eventually) a building snowpack in the Cascades. Especially after a brutally hot summer and record dry spring. It’s pouring in past of the metro area right now and we are under a Flood Watch for local areas of flooding through tomorrow. What’s ahead? Read on…

KEY POINTS

• Showers continue in the metro area and south tonight, while heavy rain continues most of night in a line from Tillamook to Longview and northward.
• Steadier rain develops later tonight in the metro area and south, continuing through Friday afternoon. The morning commute and midday will be a soaker again!
• Rain comes to an end all areas west of the Cascades around sunset Friday
• Saturday should be dry
• Rain returns north of Portland Sunday, we’ll be right on the edge of that rain line in the city. Definitely dry south and east of here Sunday too.
• Expect another 2-4″ Coast, Coast Range, and Cascades. 1.00-1.50″ metro, and 2-3″ Longview up to Olympia the next 24 hours

This is what we’ve seen so far; a big dousing central/south Willamette Valley last night, but then heavier rain shifted north of Portland most of today. Of course mountains both east and west of us have been significantly wetter

Notice Portland is one of the driest spots. That’s not unusual. In fact check out the typical yearly rainfall in the Portland/Vancouver area. Charlie Feris retired from BPA many years ago, but continues to maintain a precipitation network of observers. He’s been doing it since about the time I was born!

Precipitable Water chart shows that we are most definitely under an atmospheric river (pineapple express) right now. Let’s just call it an “AR” so I don’t have to type it out each time. Look at that slug of tropical moisture stretching 2,500+ miles from near Hawaii to Washington!

A tool we use to analyze this situation is Integrated Water Vapor Transport (IVT). Basically how much water vapor is being transported in any one location through a cross-section of the atmosphere. Chart below is 4pm today. Numbers show total mass of water vapor passing through each square meter of the AR each second. Got that? Simpler: Bigger numbers equal more moisture moving through any one spot overhead.

You may notice there isn’t much “IVT” going on east of the Cascades. Where did all that water go? It was converted into rain. That “river of water” in the atmosphere slams into the Coast Ranges, then the Cascades. Rising air cools, and moisture must condense into droplets = rain. The heaviest rains fall where high IVT encounters a mountain range perpendicular to the flow. Westerly flow squeezes maximum rain out of these ARs with our north/south oriented mountain ranges. That’s why so much more rain falls west and east of downtown Portland compared to the city itself.

Alright, so the AR is aimed at Washington right now and through much of tonight. By tomorrow morning it has weakened just a bit, but dropping south over Oregon. But don’t worry, there’s still plenty of rain to go around

Then it has fallen apart by Saturday morning, ending the rain over most of Oregon

An even more intense AR sets up Sunday, but this time it’s aimed at Vancouver and NW Washington. We will be right on the edge of that one.

How much rain is ahead? I think the 18z ECMWF shows a good approximation of what we can expect the next 24 hours. Less than 2″ for most areas south of Longview in the lowlands. Up to another 4″ in the wettest parts of the Cascades and Coast Range

We will probably end up with 2″+ in Portland out of this event, pretty good model forecasts so far…

The final part of this AR moves south over us Monday, followed by colder air; snow levels will go below the passes Monday night. But then a relatively dry and cool-ish pattern follows much of next week. The GFS model’s ensemble forecast for Salem high/low temps gives you the general idea.

There’s no sign of a stormy pattern OR low elevation cold/snow in the next 10 days. That can happen once we hit mid-November.

That’s it for now. I’ll be on TV at 8/9pm on FOX12Plus and 10/11pm on FOX12, see you there!

Chief Meteorologist Mark Nelsen

Fall So Far, Plus A Pineapple Express Ahead

9pm Monday…

Time is flying, or maybe I’m just getting older. We’re quickly heading toward mid-November so let’s do a quick recap of the season so far.

Meteorological Fall includes September/October/November, so we only have 3 weeks left this season:

1. Temperatures have been near normal, or slightly below since September 1st. September and November (so far) slightly warmer than normal, but October slightly cooler than average. Nothing interesting here
2. Wet! After an incredibly dry spring/summer, rainy weather arrived in mid-September. We are very fortunate it didn’t wait a few more weeks. It’s always amazing how we go from desiccated/dry ground and brown vegetation to green within just a few weeks each fall. Since that time, 8.87″ rain has fallen in Portland! As always, the mountains scoop up lots more rain. Mt. Hood Test Site at the bottom of Timberline’s Pucci Lift has seen 15.30″. North Fork SNOTEL south of Multnomah Falls at 4,000′ picked up 27.70″. A SNOTEL station named “Sheep Canyon” is on the southwestern slopes of Mt. St. Helens. In that notoriously wet location, over 3 FEET of rain has fallen since the wet season began; 37.40″. It’s hard to believe, but those numbers are about normal for this point in the fall. The Cascades are very wet (or white) late September through springtime!

Here are some other numbers showing just the last 30 days. Screaming message here is that you shouldn’t complain about rain in the I-5 corridor…tons more rain regularly falls west and east in hills/mountains surrounding the lowlands.

SUMMARY: THIS FALL HAS BEEN QUITE “NORMAL” SO FAR

November is here and it’s one of the 3 wettest months of the year west of the Cascades. November, December, & January are close to the same rain-wise. It’s also the month that we slowly slip into our “winter” conditions west of the mountains. High temperatures drop down through the 50s.

WHAT’S AHEAD?

More wet weather. Sure, today was amazing with early blue sky and comfortable temps in the 50s. But a relatively weak system is sweeping north along the coastline; we’ve got a wet night ahead. The Cascades picked up 4-12″ snow over the weekend, and I expect another 4-6″ through tomorrow above 3,000′. But don’t get excited about an early start to the ski season yet…

PINEAPPLE EXPRESS

Starting Wednesday, upper-level ridging pushes warmer air north along the West Coast. That ridge LOOKS strong enough to give us warm & dry weather Thursday based on this map

But plenty of warm & subtropical air will be flowing northeast from north of Hawaii. Check out “Precipitable Water” on Thursday. You can see why these narrow ribbons of warm/moist air are named “Atmospheric Rivers”.

When it’s a warm one like this, freezing levels soaring over 9,000′, we also call it a “Pineapple Express”. Same idea, a warm, cloudy, and very wet weather pattern for us.

Since this is like a narrow firehose of rain that flips around easily, forecast rainfall can be all over the place as well. The ECMWF forecast through Friday morning seems a bit excessive showing 2-4″ in the western valleys of Oregon and SW Washington just through that time.

It’s better to use “model ensembles” in a situation like this. For Salem, the 51 members of the ECMWF model show an average of 2.50″. That’s the bottom half of the chart. Each of the horizontal lines on the top half show accumulating rainfall the next 6 days (at Salem)

For this reason (and at this moment), the event late Wednesday through Friday does not appear to be a significant flood producer. But, always something to watch as we get closer.

Snow levels will be very high Wednesday night through Sunday, mainly above 8,000′.

Add 3-6″ of rain to a fresh foot of snow later this week and and you can guess what will happen. There won’t be much left. But hopefully a bit colder next week and MAYBE some ski terrain opening up for the weekend before Thanksgiving…we will see!

To sum things up…it’s going to be very wet this week, especially Wednesday night through Friday. But models are also implying the ridging pushes most or all of the rain north of us next weekend. I’m skeptical…more later in the week

Chief Meteorologist Mark Nelsen