Put A Fork In It; Winter is “Over” West of the Cascades

February 25, 2021

10pm Thursday…

Our mild winter (minus one cold week in mid-February) has come to a conclusion in the lower elevations west of the Cascades. As I look into the first week of March on our various models, it’s pretty obvious that

It’s time to put a fork in Winter 2020-2021.  This season is finished

So what kind of a statement is that?

It means I’m quite confident we’re done with most of our typical winter weather events.  But not all!  Read on…

First, this winter (December 1st to now) is running 13th warmest on record at PDX.  Those records extend back to 1940.  Spokane is 14th warmest out of 72, and Baker City is experienced its 12th warmest winter.  So not a record warm winter, but definitely at the upper end for many spots. This “La Niña Winter” will go down as warmer than average.

Looking at the models for the next 10-14 days…

  1. I don’t see an outbreak of cold arctic air.  For that matter I don’t see unusually chilly air for this time of year.   We have not seen a region-wide arctic air-mass descend across the Pacific Northwest since December 2013!  Sure, some cold-air intrusions to some areas at times, but no big arctic blast.
  2. I don’t see a setup for lowland snow west of the Cascades.  Even a brief & wet morning snowfall.

Point #1 on the graphic below is most important; the chance of a widespread snow/ice event in the metro area is down to just about zero.  I mean the type of event that shuts down our area for a day, or even part of it.

  • Other than the cold spell with the snow/ice storm, we didn’t have a major freeze this winter. Portland’s low temperature was 24.
  • Sure, we can still get a chilly east wind, but in early March we don’t get long periods of the screaming cold easterly wind.
  • As for flooding, for the first time in my career we DID see some significant April flooding in Spring 2018.  But otherwise all of our big floods have occurred during the winter months.

What could we still see as we head into March?

We have seen March windstorms in the past and even one April event a a few years ago.   And of course in recent years we’ve seen close calls with snow in March, including last year.  Although it’s still far more rare than December-February snow.

What actions can YOU take at this point?   Get those snow tires off and turn on the water to the chicken coop (mine is back on).

There you go.  Basically it’s time to “de-winterize” WEST OF THE CASCADES.

SUMMARY

We transition from late winter to early spring weather over the next 2-3 weeks as temperatures gradually rise.

In the short term, we’ve got big-time winter in the Cascades! Winter Storm Warnings are up for there and in Northeast Oregon.

Chief Meteorologist Mark Nelsen


Best Mid-February Cascade Snowpack In Years, Plus A Few More Storm Stats

February 17, 2021

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


The Big Thaw Today; Back To Normal

February 15, 2021

9pm Monday…

Quite a change today eh? Temperatures soared from near/below freezing yesterday evening into the upper 40s or even lower 50s today. The southwest wind did the trick; even Troutdale made it to 48. I think the McMinnville sensor may be about 5-6 degrees off, more likely 50 there.

A westerly surge of “warm” air is working through the Gorge. Cascade Locks has jumped into the lower 40s and Hood River should see it soon. By sunrise a 40-45 degree breeze should have made it all the way to Maryhill & beyond. The pressure gradient is now WESTERLY for the first time since last Wednesday in the Gorge. This cold event has ended.

The damage to the power grid is the biggest I’ve seen since the 1995 windstorm. Looks like around 300,000 PGE customers have been out at one time in two different “waves of ice”. The first Friday night in the northern/central Willamette Valley, then the 2nd yesterday evening/last night in south and east metro areas. There was some overlap in those south metro spots. Here are some preliminary ice accumulation numbers. It’s amazing how well models did showing the thick ice glazing in the southern half of metro area. I’ve colored the areas where we generally saw 1/2″ or more.

The rest of this week features “normal” weather. Drier conditions tomorrow with just a few scattered showers, but heavy Cascade snowfall. Then ONE dry day Wednesday before rains resume Thursday & beyond.

A few notes:

  1. We don’t see a February 1996 setup with flooding following the melt. There’s no heavy rain on the way to bring us a flood.
  2. I don’t expect re-freezing of wet roads tonight. Too mild with cloud cover for just about all areas west of the Cascades
  3. There’s no sign of low elevation cold/snow in the next 10 days, but we’ll remain on the cool side with lots of rain

Chief Meteorologist Mark Nelsen


Freezing Rain For Some This Evening: Temperatures Continue Rising Tonight

February 14, 2021

9:30pm Sunday…

There comes a time at the end of these cold east wind events where the airmass pouring out of the Gorge becomes so thin that parts of the metro area “pop out” into the milder air above. That appears to be happening in the higher elevations of the metro area right now. Chehalem Mountain is up to 37 degrees. Top of Mt. Scott from 28 at noon to 32 now (still rising), Larch Mtn. Washington has jumped to 38 with a south wind (and rising). These areas are all near the 1,000′ elevation. Fascinating meteorologically because up until early afternoon these were the COLDEST spots in the metro area. Because there were higher up in the cold westward flowing air from eastern Oregon/Washington. Folks, this brief cold/ice/snow episode is just hours away from finishing…I’ve seen it many times. Once it warms in the hills around town the game is just about over. Notice ALL metro temps are at/above 30 degrees now. The only 20s are left in the western Gorge, around Corbett and east of Washougal.

Don’t get me wrong, at 30-32 degrees ice can still accumulate on trees and powerlines = bad. But it can’t last much longer now. The snow level is up around 5,000′ this evening in the “warm” airmass overhead, that’s why we’re seeing liquid raindrops falling through this thin cold layer and freezing on contact (in spots) instead of snow.

The pressure gradient is 7-8 millibars easterly through the Gorge, and the wind is still blowing hard out there, confined to a layer less than 2,000′ thick. That goes to zero around 9-10am. In fact a westerly surge works through the Gorge later tomorrow afternoon = much warmer!

So we’ve got a few more hours of icing, then not much rain at all after 2am as this system moves off to the east. It’ll be mainly dry for the morning commute. As mentioned in the previous blog post, I expect a southerly surge of wind up the valley after 4am as a surface low pressure tracks by to the north. You can see the switch and temperature jump into the 40s sometime after 7am in Portland

KEY POINTS

  • Expect a bit of additional icing the next few hours mainly east of I-205 and into the Gorge. Still a bit more in higher elevations of SW Portland & the West Hills, but most of forecast ice glazing on graphics below has already happened. We should be more dry than wet after 2am and through the morning commute.
  • Temperatures hover between 30-34 in most of metro area through 6am, then jump into the low-mid 40s between 6-10am. Expect quick thawing by late morning. Lots of water all over the place…
  • 6-10″ total snow in the Gorge through morning with temps below freezing until noon or so. But even there a westerly wind should push all of you up into the 30s by dinnertime and beyond.
  • The rest of tomorrow and this week will be uneventful with lighter showers Tuesday, dry Wednesday, then some cool/wet soakers into next weekend. Up to 2 feet more snow will fall in the Cascades these next two days. Oregon will be back to normal snowpack-wise within the next few days! Nice La Niña catch-up.

I’ll be on TV at 10 & 11pm tonight…Chief Meteorologist Mark Nelsen


Cold Air Lingers One More Day; Then Warmer

February 13, 2021

7:30pm Saturday…

The February 11th-13th 2021 snow/ice storm is going to be one for the record books. A few stats for you:

  1. PDX only made it to 30 degrees today; for the 2nd consecutive day. That’s a rare event this late in the season. In fact only TWICE has PDX stayed at/below 30 degrees after the first week of February. In 1956 and 1960. We haven’t seen such a cold day this late in the season during my lifetime…brrr!
  2. The Portland forecast office has picked up 8.0″ snow so far, plus I wouldn’t be surprised to see a bit more this next hour or two since it is snowing right now. That makes it the 4th snowiest February on record, or maybe it’ll be #3 within a couple hours

3. At the peak earlier today, Portland General Electric was reporting about 220,000 outages due to the catastrophic ice storm in the northern and central Willamette Valley. That is a similar percentage of customers we’ve seen during previous big ice storm events. But those have generally been central/east metro closer to the Gorge. This time everything went wrong. A thin subfreezing layer of air at the surface plus heavy precipitation overhead.

Looking ahead…

KEY POINTS

Light mixed precipitation continues tonight through tomorrow morning throughout the region. In the Portland metro area it could be snow or freezing rain through sunrise. We are getting the typical showers between organized weather systems.

The entire metro area stays frozen tonight. Typically the showers putting down a fresh swath of light snow or a bit of freezing rain glazing would be a HUGE deal; but everything is covered in snow or ice already. Adding another inch or two of snow shouldn’t change things much.

Another slug of steadier precipitation comes through midday/afternoon tomorrow. BUT, at this point it’s warmed overhead so we’re into liquid precipitation only. Temperatures rise into low-mid 30s metro area (away from Gorge) and that means we shouldn’t see additional icing of roads tomorrow. In fact light rain showers will help melt things a bit. Tomorrow afternoon a southerly wind pushes up to the south edge of metro. Everyone in a line from Newberg to Wilsonville to Molalla and south should see temperatures jump into the 40s. We stay between 30-37 in the rest of metro.

Tomorrow night one last slug of steady rain comes inland. The last “holdout” of sub-freezing air will be east of I-205 and near the Columbia River from the airport to mouth of the Gorge. These areas (Troutdale, Gresham, East Portland) will see significant ice glazing tomorrow afternoon and night. Possibly up in the West Hills as well…maybe. I think the rest of the metro area will sit at 32-35 degrees tomorrow night which means no additional icing.

Finally, a mild southerly wind pushes through the ENTIRE metro area by sunrise Monday. We will immediately jump into the low-mid 40s at that point…MONDAY IS THE BIG MELT DAY. West wind pushes through the Gorge Monday as well, but midday/PM

TECHNICAL INFO

It was a somewhat poor choice to drive home last night; probably should have stayed at hotel one more night. 1-3 foot high snowdrifts…an experience like those Subaru commercials. I followed my son in his 4Runner through those drifts between Corbett and Vista House. That is the deepest snow I’ve driven through (separated by bare spots in the wind). Much better coming back to work today because Multnomah County and ODOT road crews have been working so hard. It was neat to be behind an ODOT plow blowing through those drifts today; an massive explosion of beautiful powdery white passing through each one.

This cold airmass is just about played out, we saw quite a bit of melting at 1,800′ on our KPTV tower cam today. That means the cold layer is now that shallow overhead. Snow level from the Astoria profiler is around 2,300′ or so right now, which means the cold air coming out of the Gorge is still thick enough to “fill the gap” and keep temps at/below freezing all the way down to the city. That’s why we’re seeing snow this evening.

That will change around sunrise tomorrow. WRF-GFS sounding for right now shows at/below freezing all the way down.

But by 10am tomorrow, a warmer layer has moved in (temp above zero C) = all liquid rain in the metro area from this point forward. The red line is temperature, blue is dewpoint

At 1pm tomorrow a weak front is moving onto the coastline, keeping easterly wind going through the Gorge. It’s calm in the Willamette Valley.

But then a 2nd/stronger system sweeps toward the coast tomorrow night. This time the surface low is headed north of us. At 1am tomorrow night, east wind is screaming through the Gorge again, although it’s a thin layer of cold air compared to yesterday. Warm southerly wind has reached up to about Salem.

Then at 7am the low is pushing across SW Washington. Gusty southerly wind has arrived in the metro area; temperatures suddenly pop into the mid 40s around sunrise…the melt is on.

Whatever falls from tomorrow morning through late tomorrow night will likely be freezing rain east of I-205 near and south of the Columbia River. Expect 1/4″ to 3/4″ glazing over there and into the western Gorge. Cold air will be deep enough for snow in the central and eastern Gorge until a warming west wind arrives Monday midday/PM. Seems unlikely that I-84 will reopen before Monday.

I’ll be on TV tonight at 10pm, and of course tomorrow night at 5/10/11pm. Chief Meteorologist Mark Nelsen


Historic Ice/Snow Storm Ending; Midday Saturday Update

February 13, 2021

11:30am Saturday…

This will be the shortest post of the week because I need to get to work! Busy with snow blower this morning…

KEY POINTS

All Winter Storm Warnings and Ice Storm Warnings in lower elevations end by 4pm. After 7am or so we transitioned to scattered off/on showers across the region so we DO NOT EXPECT SIGNIFICANT SNOW ACCUMULATION OR ICE GLAZING FROM THIS POINT FORWARD.

Sure enough, on the back side of the system it DID change back to snow across middle of metro area. Looks like most of us metro area and north picked up 1-3″ after that point

A catastrophic ice storm has occurred in the mid and north Willamette Valley; not seen in at least 50 years. PGE alone has over 200,000 outages. Far more damage has been done (more ice this time) than with December 2008 event.

From this point through tomorrow afternoon we’ll see off/on showers. Some warm air (above freezing) is working into the central Willamette Valley; we’ll see how far north it makes it.

Warming overhead means generally whatever falls after midnight tonight will be liquid in the metro area. Most of us will be below freezing, so of course that will add some ice glazing. Not that it matters much at this point with so much snow/ice on the ground.

I’ll be on TV all afternoon and evening as we show you all the sights/sounds of this historic event! Here’s a pic from Jeff Raetz down in Oregon City…over an inch of ice glazing!

Chief Meteorologist Mark Nelsen


Friday Evening Storm Update: Heavy Snow & Freezing Rain Next 8 Hours

February 12, 2021

9:45pm Friday…

Quick update to let you know what’s going on as we are getting slammed by Round #2

  1. Heavy precipitation continues until around 5am Saturday, then it’s just scattered showers. This event is going to be pretty much “over” by mid-morning tomorrow. By that I mean I don’t expect significant accumulation of either snow/ice pellets/freezing rain after sunrise tomorrow.
  2. The entire metro area is now the coldest we’ve seen through the event. Low to mid 20s and in some areas it’s pouring down liquid rain! That’s not good.
  3. Portland officially recorded at least 4.7″ snow today, possibly a bit more since 4pm

One relatively minor change, which makes a big difference for snow totals is here. This is what we’ve been expecting. Snow north metro, freezing rain far south for this event.

This is what has actually been occurring…do you see any difference?

Yep, that’s about a 10 mile northward shift to the MIX and FREEZING RAIN AREA. Meteorologically pretty close, but it happens to lie right across the middle of a metro area containing 2.5 million people!

5-7″ snow has fallen in the snowy area so far (as expected), but more glazing is happening farther north in the metro. Those places in the central metro that might have seen 4-8″ instead are mostly done with snow.

So in the end we’ll still end up with 2-12″ total snowfall in the metro area, but the southern end of light snow shifts a bit farther north.

Models are hinting that we may see a southward shift of the snow line again late tonight as cooler air comes in with the front…before precipitation totally cuts off. SO IT’S STILL POSSIBLY ANYONE IN THAT MIX AREA PICKS UP 1-2″ LATER

That’s it for now…see you on TV at 10/11pm…Chief Meteorologist Mark Nelsen