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  • Posted

Monday, Oct. 25th, 3:30 P.M.

It’s a soaker out there this evening as waves of showers continue to roll in from the Pacific.  An unstable airmass means some of the showers are heavy and there’s still a slight chance for a thunderstorm through the evening.  Wind dies down a bit overnight, but at least some southerly breeze continues all through Tuesday.  That makes for a mild night around 50 degrees again.

A more organized weather system arrives at sunrise for a very gloomy first half of Tuesday, wet too!  Then it’s more of an off/on showery thing tomorrow afternoon and night.

Wednesday and Thursday we’ll see the weather “slow down” a bit with more dry than wet days.  But still a lot of cloud cover.  After a wet day Friday, there’s a very good chance we have a few dry days into the weekend and early next week!  A dry easterly wind may give us lots of sunshine on Halloween.

  • Posted

A short blog post tonight! Just to point out how quickly the snow/water situation is going downhill as this warm-ish and VERY DRY spring continues…

Snowpack on April 1st…pretty good across Northern Oregon, below average across the southern half of the state

Today…what a change! Much worse. The extremely dry April and warm temperatures have taken a big toll

Now it’s important to point out that early & end of season maps can be deceiving. For example there are many lower elevation stations that don’t typically still have snow on the ground in early May. That could skew the average. But the point is that things are heading downhill quickly and I don’t see any change through mid-May. Take a look at the Mt. Hood Test Site near the bottom of Pucci lift at Timberline (5,400′)

The GREEN line is the typical accumulation of “snow water” through the season. The colored areas represent lowest to highest snowpack on record on any one date. Green area is an “average” year. At this elevation, the abundant February snows brought the snowpack up well above average (BLACK line). And a cool March preserved that snow. However the lack of precipitation in March means a peak occurred a bit earlier than normal. Now it has slipped below average! Basically A GREAT SNOWPACK IN LATE FEBRUARY AND EARLY MARCH IS NOW MELTING FASTER THAN NORMAL. The whole snowmelt season is earlier and more condensed this year. At this rate there won’t be snow on the ground more than another month…unless we go back to cool and wet weather.

Farther east, in the Blue Mountains, this site shows something similar…well above normal snowpack in March, then a rapid melt right now. It’ll be gone in a couple days…earlier than normal!

This spells trouble for our water supply. In fact Willamette Valley Project reservoirs are running well below where they should be in late spring. Most of these lakes reach their maximum “full pool” level at the end of the spring filling season. That’s right now. But two months of very little rain is a big problem.

Detroit Lake (one example) is about 17 feet below where it should be.

So…we need rain, but I don’t see anything significant through the next week. I’ve never seen it this dry at this point in the spring.

Chief Meteorologist Mark Nelsen

  • Posted

Saturday marks the first day of astronomical spring and the outlook is grim for the western portion of the country, where drought conditions will persist.

  • Posted

9:30pm Wednesday…

We’ve had three mild days with sunbreaks at times, and that’s melting the snow nicely west of the Cascades. After peaking out around 14″ at home, I’m down to just a few inches now (quite a bit denser!). But during this time a big snowstorm has been ongoing in the Cascades.

At this moment Mt. Hood Meadows has a 132″ base, Timberline 154, and 70″ (six feet!) is on the ground down at Government Camp.

I just checked out the numbers at the Mt. Hood Test Site (SNOTEL) at 5,400′. This is a long term snow measurement site in operation for over 40 years now. It’s close to the bottom of Pucci Lift in the Timberline Ski Area. What a surprise! Snow depth is 138″. If you could snap your fingers, immediately melting all that snow, it would be the equivalent of 47.7″ rain. That is referred to as “Snow Water Equivalent” or SWE. This is how our summer water supply is measured. Snow “stored” in the Cascades (and other Oregon mountains) gradually melts March through June, delivering water into reservoirs and recharging groundwater. We have a long dry season so snowpack is very important.

What surprised me is how well the snowpack is doing; at that elevation on Mt. Hood, AND down around 4,000′ (two separate sites), it’s THE BEST SNOWPACK ON FEBRUARY 17TH SINCE 2008!

To get a more complete picture, scientists at USDA average many stations across the region and state. For the Mt. Hood area, we’ve gone from 66% of average early in the month to 99% today…big improvement in just a couple weeks! All of Oregon looks like this…

We are in good shape, best across the northern part of the state. It appears we’ll be staying on the “cool-ish” side of things for the next 7-10 days. The chart below shows 850mb temps from each of the 51 ECMWF ensemble members for the next week. That’s temperature around 5,000′ elevation for the next two weeks. The green line is the average for this time of year. Red line is average of all 51 members. What sticks out? Much of the time the next two weeks, the overhead atmosphere is below that green line = cooler than normal. Good for Cascade snow, bad if you want some (very early) spring weather in the lowlands. That said, we need a temperature below -7 this time of year for a wet morning snowfall. That can still happen into mid-March, although rare. There are a few members implying that could happens in the next two weeks…we’ll see. Regardless, I’m turning my outdoor chicken water back on; no sign of a cold freeze.

Speaking of lowland weather, plenty of rain ahead, although I don’t see any sort of flooding setup. There are hints that MAYBE later next week it might turn slightly drier. You can see more gaps in the Euro ensemble 24hr QPF chart beyond the 24th.

On another subject, we picked up some new numbers from PGE today. They now say that at one point 350,000 customers were out of power. That makes this the most disruptive power event since the Columbus Day Storm (in pure numbers). That’s about 40% of their customers! In terms of percentage of customers, the December 1995 windstorm put 46% of customers out, so these two events are comparable in that way I suppose. Just a devastating ice storm for utilities and life-altering for many of you this week.

On the snow front, it turns out I had a bad number for 1955 (see previous posts). So the 10.1″ that fell in Portland (officially) through this event gives us the 2nd snowiest February on record

That’s it for tonight, I’ll be off for a few days and back Sunday…Chief Meteorologist Mark Nelsen

  • Posted

9:30pm Sunday...

Here we are in mid-January, halfway through meteorological winter (December-February). We've had ONE significant weather event during that time west of the Cascades; the wind and rain storm earlier last week. It has been a very mild winter as well. By the way, I just confirmed the peak gust at PDX was 50 mph during the last minute of January 12th (11:59pm).

December 1st through January 16th has been the WARMEST 1ST HALF OF WINTER ON RECORD IN PORTLAND! You like that big red font? This comes with one big caveat. Portland has grown tremendously and we have an "urban heat island" now. It's most noticeable at night. A lot more people live here compared to 60 years ago. That means even if the climate was not warming (it is), we would be seeing Portland's average temperature rising due to that effect alone. But check out Redmond (little/no urban influence there). It's the warmest since 1951! And Olympia has seen the 3rd warmest after 1951 & 1981. Going back 100 years, Salem has seen its 5th warmest first half of winter. My point is that yes, it has been a very mild far.

Snowpack is well below normal, running about 60-80% of average in the Cascades. Yet 2018, 2012, & 2011 La Nina years saw similar or lower snowpack at this point around Government Camp. Many of these years we play "catch-up" with snowpack in February/March. We'll see.

Of course weatherwise it's been a very slow winter (again) for forecasters but we think that will be changing as we head into a colder weather pattern. And yes, we may be flirting with low-elevation snow at some point in the next 10 days.

Quick Summary

  1. The next 7 days will be much drier than average, it's possible we don't seen any rain until NEXT Sunday
  2. There's no sign of an "arctic blast pipe-buster" for at least the next 10 days. That is a big shot of cold air from Canada; think lows in teens or lower and highs around 30 or below. I don't see that happening.
  3. Beginning next Sunday, expect a cold & wet weather pattern with heavy Cascade snowfall
  4. Beginning next Sunday, we may see our first widespread foothill and Coast Range snow plus there may be more beyond that. This winter, sticking snow below 2,000' has been rare. That will change for the final week of January. If you live between 1,000' and 2,000', you can expect to see snow more regularly beginning next Sunday.
  5. AT THIS POINT, we do not have (sticking) snow in our forecast (for lowlands) through at least next Sunday. That's because we don't see a setup that would drag sticking snow all the way down to the valley floor, or sea level. But it may be close to sea level at some point in the 7-10 day range. Keep a close eye on that Sunday-Tuesday forecast NEXT week.

What's Changing?

We have a strong upper-level ridge right over us and it's staying put through Wednesday. This is the flow of air up around 18,000' (500mb). I've annotated the ridge with a yellow line. This is Tuesday

By Thursday, a cold upper-level trough is dropping down the back side of the ridge as it backs off to the west.

But it appears just about all moisture will remain offshore, so we're going with just a few light showers (rain) Thursday evening. Weather geeks will remember that THIS was going to be the big system that would drop south and bring in arctic air at the end of the week. That was on some models maybe 5-7 days ago. Now it's just a weak ripple in the northwesterly flow. Then by Monday the 25th, a much deeper & colder trough is moving into the Pacific Northwest

This one is preceded by a stronger cold front and plenty of moisture next Sunday. Depending on the exact track of surface low pressure, this setup CAN bring snow to sea level. I've got two thoughts on that. First, neither the GFS or ECMWF models at this moment retain enough cold offshore flow to bring widespread sticking snow to the valley floor. That's because the low is coming in from the northwest. Second, the air isn't that cold to begin with and we're quickly going to onshore (mild) flow. That's almost always a snow killer. That system next Sunday reminds me of several during the 2007-2008 winter that brought abundant snow to Detroit, the Gorge, Coast Range, and the Cascade foothills. But not quite cold enough for lowest elevations to get in on the snow action. 850mb temperatures are forecast to be around -5 to -6...again, not quite cold enough for a big snow event in the metro area next Sunday. I think the ECMWF rain/snow forecast shows the situation well for Sunday night

Beyond that, the upper-ridging wants to move even farther west of us, allowing a cold trough to set up over the Gulf of Alaska and send cold waves of moisture our way. A quick animation of those upper-level heights from next Monday the 25th to Monday February 1st (a full week), shows the progression westward, along with the coldest air

The final image tells me a lot.

It says that beyond about day 10, we're into a classic La Nina pattern that's wet and cool. Tons of mountain snow, but not much chance for it in the lowlands. This will likely be the first big week of mountain snow this winter, maybe like the middle of last January?

Check out the GFS ensemble forecasts for snow. About 1/3 to 1/2 produce "sleddable" snow in Portland sometime in the next 2 weeks. I think that might be generous considering what I'm seeing right now.

You can see model forecasts of high temperature (usually a few degrees low) dip to a minimum early NEXT week and then rise again as we get more systems off the mild Pacific. This is the GFS.

One more thing that gives me confidence that we're not headed into a major cold/snowy spell...the 850mb ensemble charts. Excellent agreement through the next 7-9 days, then a rise (warming). Almost no members below -7 through the next two weeks. This is just the ECMWF, but GFS is similar.

This wasn't the case 5-7 days ago. As we get closer to a change, models come together most of the time and this is a good example.

That's it for now. Of course even without a "major cold/snowy spell", we can get an event where part of the lowlands get snow and that may not show up until just a few days ahead of time. I'll be working regular shifts for the next 3-4 weeks as we wrap up this "winter". We should still be having some fun even if no widespread snowstorm shows up in the valleys.

Make sure you follow me on Facebook @marknelsenweather, Twitter: @marknelsenKPTV, I update those far more often than this blog. And don't forget our podcasts here:

Chief Meteorologist Mark Nelsen

  • Posted

8pm Sunday...

We had our first taste of the cold season "fog inversion" this weekend. That means cool air remained in the valleys while the atmosphere overhead warmed. Yesterday Portland only made it up to 41 degrees...quite a taste of a typical winter day around here

Which brings up a good point...from a meteorological point of view we've pretty much entered "winter" west of the Cascades. I suppose it seems like a ridiculous thing to say with a week still left in November right? Nope, once we hit mid/late November, we've entered the busy three months of the year in our area. "Winter" tends to come early and melt away a bit quicker than in colder continental climates. No, I don't mean just snowfall. I'm referring to our usual weather events in wintertime.

It's EXTREMELY rare to see a real arctic blast outside of this window. And if we're going to have an "all-day" snow event in the lowlands, the type where roads stay frozen, it happens during this time. Remember the past few years? When we've seen snow from mid-February onward the effects on lowland roadways are minimal mid-late day. That's because of increasing sun angle. If we get significant flooding this year, most likely it'll be within the next three months.

What's Ahead?

I took a few extra days off this past week; still have a few leftovers from our summer furlough days. When I came back in to the station today I noticed three specific items while perusing all the models/maps:

  1. I don't see a stormy weather pattern in the next 10 days
  2. After a wet Tuesday/Wednesday, we're headed into a drier weather pattern through at least the first few days of December
  3. There's no sign of lowland snow/ice or an arctic blast in the next two weeks. That means most likely we won't be seeing an early freeze this year (November or early December).

Basically the weather looks a bit on the slow side over the next 1-2 weeks. In the short term I see a couple weak systems moving inland tonight, then a stronger cold front and chilly airmass Tuesday/Wednesday. We should see another 1/2" rain early this week out of these systems.

Beyond Wednesday, upper-level ridging wants to be the dominant weather feature over the western USA for awhile. Take a look at 500mb height map from Canadian ensembles for this Friday

and then 10 days from now...Wednesday the 2nd

I think the ridging may be overdone on this model, other models show above average heights but not so extreme.

Weak (and wet) systems will probably still be coming through the ridge during this time, I don't think it'll be one of those "completely dry for 10 days" setups. But this eliminates the chance for any significant cold spell and/or snow in the lowlands for the next 10+ days.

Ski Area Weather

We've got a fantastic early season snowpack on the ground in the Cascades above about 3,500'. These numbers a bit deceiving since the average snowpack is very low this time of year; anything significant is way above the average. But you get the idea...

Both Timberline and Mt. Hood Meadows have about a 3 foot (or more) snowpack on the ground now. Even Government Camp has somewhere between 4-10". In other years those first two ski areas would already be open, but of course COVID is throwing things off. Regardless, the slopes are just about ready! Timberline is opening this Wednesday the 25th and Meadows is opening for the season Monday the 30th! I don't see anything that would stop either from happening. Another foot or so should fall above Government Camp by Thanksgiving morning. At least according to the ECMWF model

The only possible rainy weather at the ski resorts would be Friday night or early Saturday as a weak system moves through the warm upper-ridge. So we should remain in good shape for an early start to the ski season through at least early next week. We'll see what happens beyond.

Enjoy the showers early this week; I'm focused on the dry weather later in the week. After Thanksgiving Day it's the Christmas season...good weather to hang some lights Friday-Sunday!

Chief Meteorologist Mark Nelsen

  • Posted

7pm Friday...

Last night was fun...strong wind arrived right on schedule. The first wind storm of the season produced widespread 50-65 mph gusts along the coastline. Of course the usual high wind spots recorded much higher speeds.

In the inland areas peak speeds were a bit lighter than models were forecasting, although close enough to our 35-50 mph forecast. PDX hit 37 mph. Around 7,000 PGE customers lost power in the northern Willamette Valley.

We picked up a LOT of rain, you probably noticed!

If there were any doubts this would be a dry November...that's disappearing quickly.

We have November snowstorm #2 in progress in the Cascades. The live view from our Upper Bowl camera at Mt. Hood Skibowl shows at least 20" on the ground up there. Last year we had trouble getting that much all the way through late December!

About a foot and a half of new snow has fallen above 5,000'!

Both Timberline and Meadows now have a base around 30"...ON NOVEMBER 13TH. This is way ahead of last year when ski areas had less snow on the ground the third week of December! Excellent news.

So what's ahead?

Lots more rain in the valleys, and snow in the mountains. Another system moves inland tomorrow afternoon/evening; snow sticks above about the 3,500' elevation. That snow level does go as high as 4,500' early Sunday, then drops by midday. The result should be another 8-12" in the Cascades by Sunday evening when things dry out. I do expect a "warm" system in the mountains Monday and early Tuesday, but then we're back to cooler systems the 2nd half of next week.

To summarize:

  1. Cascade ski resorts appear to be in excellent shape for early openings this year. In the past few years ski areas have opened with limited operations with only 20" on the ground.
  2. There WILL be a 2 day spell of rain/warm conditions, but not really a pineapple express. I expect the snowpack to consolidate a bit and we'll lose quite a few inches. But more snow fill follow the 2nd half of next week.
  3. There's no sign of a warm spell or series of warm storms that would melt most of the snowpack. Good news!

This is quite a change from the past two years. Check out snow depth at the bottom of Pucci Lift. This is for November 19th (next Thursday). Last year there was nothing on the ground at this point...big improvement.

By the way, we'll see at least another inch of rain in the lowlands this weekend. Keep in mind this is precipitation; much of that falls in the form of snow in the Cascades.

Expect a soaker the 2nd half of tomorrow, plus gusty southerly wind. Then it's back to a showers/sunbreaks mix what we've seen today.

Enjoy your weekend!