Winter 2021-22 Thoughts

October 27, 2021

October 27th, 2021

About this time each fall people start asking me “What this winter will be like?” or “I’ve heard it’s going to be a bad winter!“.  Actually sometimes they start asking in August!  For the record, I’ve NEVER had a person say “I’ve heard it’s going to be an easy winter“.  Apparently most of us are quite cynical and expect the worst. 

I don’t put out a “winter forecast”.  That’s because seasonal/climate forecasting has a long way to go before we say we can “forecast” a winter.  So we’ll just call it “my thoughts” for the upcoming winter since we can at least glean a few ideas by looking over some weather tidbits.  I’ve been doing this for quite a few years and it seems to work.

For those of you with a short attention span, just three points:

  1. Plan on an “active” winter this year.  The last 3 winters were quite “boring” (most of the time) for the weather professionals. Which means they were “easy winters” for regular folks (most of the time). Of course we all remember the 4 day stretch of snow/ice around Valentine’s Day right? But most of last winter was quiet weather-wise except for that event plus some flooding in mid January. The odds are tilted toward more changeable weather this winter; I expect it to be busier here at KPTV. A better chance for a windstorm, flooding, and lowland snow.  And I doubt we’ll be locked into weather patterns for weeks/months at a time.
  2. Expect at least once we’ll see some snow or freezing rain in the metro area and lowlands west of the Cascades.  I would be surprised if we get through this entire winter without measurable snow in Portland. I’d peg the chance of “sleddable” snow at about 70% some point between November 10th and March 1st. No, we have no idea when that could happen until at least 7-10 days ahead of time 
  3. Expect a good snow year in the Cascades. Good for both water next summer and skiing during the winter.  Go ahead and plan on a normal ski season with the usual variable ski conditions from week to week. I’d give this about a 70% chance of happening too. It IS possible to get a low snow year during a La Nina winter. In fact two La Ninas back in time we saw terrible ski conditions through January! Then February/March were incredible.

SUMMARY OF THE LAST 2 WINTERS

Two winters back…2019-2020  So boring…this was our 2nd consecutive “El Nino” winter. There was a real lack of Pacific storms; it was as if the jet stream just didn’t want to perform last winter.

Last winter…2020-2021 It was a surprising La Nina winter because of the mild temperatures, plus almost nothing interesting happened weather-wise until mid January! Some widespread (light-moderate) flooding showed up at that time, but then all was quiet until a 4 day blast of cold air arrived starting February 11th. That cold air was overrun by plenty of Pacific moisture which produced a snowstorm from Portland north/east and a severe ice storm from south metro down to around Albany in the Willamette Valley. Then temperatures warmed and typical (wet) winter weather resumed. We dried out dramatically in March and April, but with plenty of cool temps.

You can check out the rest of my winter recap presentation here: https://oregonams.files.wordpress.com/2021/10/mark-nelsen-winter-weather-recap-2020-2021.pdf

So much of the past 3 winter seasons have involved a lack of storminess and drier than average weather. About time for some action don’t you think? But that’s what I thought would happen this past winter too…there’s so much we still don’t know about our climate.


WHAT’S AHEAD FOR THIS WINTER?

We have entered weak/moderate “La Nina conditions” once again this fall. Models tell us most likely it’ll be a weak to moderate event through the winter. So this will be our 2nd La Nina winter.  That can give us a few hints, definitely not a forecast, but what direction our winter might be “weighted” toward.  I’ve spent some time looking at past La Nina episodes and what happened here in the Pacific Northwest.  I based all my graphics/research on a weak/moderate event.   Right now the Oceanic Nino Index (or ONI) is in the WEAK La Nina category.  

Model consensus says we’ll likely be in a WEAK-MODERATE category during this upcoming winter.  Here’s the latest plume of ocean/atmosphere models. Anything below the “-0.5” is weak La Nina, below “-1.0” is a moderate event. Strong would be “-1.5” or lower.

Typically in these winters there are 3 effects observed to varying degrees:

  1. The north Pacific jet stream tends to be more “wavy” which means there is more of a north & south component to the jet instead of travelling straight west to east
  2. There is increased tendency for blocking somewhere in the east Pacific
  3. As a result there is sometimes more interaction of the cold Canadian air to the east and Pacific moisture with the jet stream weakening dramatically at times too.

Likely effects this winter based on a moderate La Nina event:

1.  Rainfall

I think it’s unlikely that we’ll have a drought winter; but far more likely precipitation will be above average.  La Nina winters in the Pacific Northwest are dominated by a strong jet bringing frequent disturbances across the region, interspersed with sudden ridging or northerly flow.   Then it’s back to the westerly flow.  For this reason they tend to be wet.  It’s likely the #1 most noticeable event in these winters. And the chance for “wet” is much higher in northern Oregon than the southern half of the state. Although the current weather pattern this week suggests otherwise with an incredibly wet northern California very early in the season.

1a.  Flooding

This goes with the rainfall.  For obvious reasons we tend to have more flooding events in La Nina winters due to the wetter weather. Keep in mind we haven’t seen a major regional flood in 24 years. That was 1996. Previous big flood was 1964. I wouldn’t say we are “overdue”, but one of these winters it’s going to happen again.

2.  Mountain Snow

Lots of precipitation and cool weather systems = plenty of mountain snow.  This is probably the #2 most likely event.  7 out of the last 10 La Nina winters have brought above normal snow to ALL elevations in the Cascades.  Note that there CAN be a bad year; it just happened during winter 2017-18. Ouch! Check out the mid January snowpack during 2001 & 2018…

3.  Foothill Snow

This happens in some La Nina winters…significant snow to lower elevations (1,000′-2000′).  This MAY happen again if we get a succession of cold and wet systems coming in from the west and northwest.  It didn’t happen last winter, but colder than normal ocean water is poised to the west/northwest of the PACNW.

4.  Wind Storm

We are overdue for a regionwide major windstorm here in the Pacific Northwest.  The last BIG one was December 1995.  That’s 26 years ago!  14 years before that we had the major November 1981 storm.  It’s interesting that all the La Ninas from 1950 to the mid 70s had a wind gust of 60+ mph at PDX each time!  Not as frequent since that time though.

5.  Portland Snow/Ice

This one is tough.  Anyone who says a La Nina winter means lots of snow in Portland is mistaken.  Average snowfall in weak-moderate La Ninas DOES go up a bit, but not a dramatic increase.  Three La Ninas in the last 20 years have produced a major snowfall here in Portland…December 2008, January 2017, & February 2021.  I should point out that the “cool/wet” La Nina winters sometimes produce little freezing rain because we don’t get as many inversion episodes to our east, which means less east wind in the Gorge.  We need that for a good ice storm either in the Gorge OR in Portland.

ADDITIONAL THOUGHTS:

The elephant in the living room I suppose is the fact that our winters are gradually warming, and snow in Portland is more rare than it used to be when we look back more than 70+ years. Although the past couple of decades total winter snowfall seems to have stopped it’s downward plunge.  Take a look at total snow each decade since the airport observations started about 1940. Divide by 10 to get average per winter.

And downtown records that go back to the late 1800s.  The low spot in the 80s is missing some data…it should be a bit higher…

We have always been in a marginal snow climate, but now warming temps are cutting off even more of the winter snow.  Every few winters we get a good snowstorm. We all remember that event and that pops up the long-term average.  It is interesting that the last 3 decades seem to have leveled out a bit at around 4″ per winter at both downtown and PDX locations.

WHAT ELSE COULD HAVE AN EFFECT ON OUR WINTER WEATHER?

  1. Cooler Water In Eastern Pacific There is no blob of warm water in the northeast Pacific like last fall/winter. In fact much cooler than normal now.

2. Pacific Decadal Oscillation (PDO) This is directly related to the sea surface temps. Typically during a La Nina we get a negative or “cool phase” of the PDO at the same time. Last year that was not the case. But this year we seem to be in the cool phase (right side figure below). Could that make this La Nina winter behave significantly different (cooler/wetter) compared to last year? You can read up on the PDO here: https://www.climate.gov/news-features/blogs/enso/going-out-ice-cream-first-date-pacific-decadal-oscillation

This gives the general picture

3. Anthropogenic Global Warming (Climate Change) A warming globe doesn’t necessarily mean we don’t get cold air outbreaks or snow. It can also mean the usual circulations get disrupted. For example it seems to me we just aren’t getting as much storminess over the eastern Pacific the last 3-4 years. That’s just anecdotal of course. But has something shifted the past 20 years? We don’t know, although 30 years from now, we might look back and notice something did change during this period. There is still a LOT we don’t know about climate.

That wraps it up…as always we’ll see how the winter turns out…my money (again) is on “wet”, “good Cascade snow”, and at least one “snow/ice event” in the lowlands. Maybe several, but hopefully I won’t be spending too much time at the hotel right near the TV station…

WHAT OTHERS THINK

Each autumn the Oregon chapter of the American Meteorological Society puts on a “Winter Weather Conference”. It’s my favorite meeting of the year! I have been a part of this chapter my entire career. Speakers present their thoughts/outlook/forecast for the upcoming winter. The public is always invited. Last year and just this past week we gathered virtually due to the pandemic. Interested in watching? Check out my recap, plus 5 different outlooks on our Oregon AMS web page. I was especially impressed by the passion/talent the younger folks are bringing to our chapter! There is some really good information in each of these presentations. Enjoy!

Chief Meteorologist Mark Nelsen


Bomb Cyclone #2 Wrap-Up

October 27, 2021

7pm Wednesday…

I’ve been very busy training a fill-in weather person plus lots of shows the past few days! This is an unusually short post wrapping up the big event last weekend. Since I’ve been blogging for 16 years, I often look back at past posts to “remember what happened”. Now I can search “bomb” and find this post.

That Sunday satellite view was amazing! GOES-17 lightning mapping is on there as an overlay showing some thunderstorms along the coastline midday Sunday

4 POINTS

1. Models were amazing…942 millibars was the deepest low pressure Sunday morning. You can see the path of both “bomb cyclones” in the past week (surface lows). GFS/GEM/ECMWF all had the low bottoming out with 2 mb of what actually occurred.

2. Models also did very well showing the big wind remaining offshore and this wouldn’t be a significant event when we look back on the cool season (next spring). Aside from the squall line that moved through midday Sunday, most gusts were in the 25-40 mph range; hardly notable

3. A line of showers and a few embedded thunderstorms move through the metro area midday Sunday. In a few spots strong wind overhead mixed down to the surface. The 43 mph gust at PDX occurred at this time. But Aurora hit 51 and Salem 57! It was a real hit/miss thing and it’s notable that Portland NWS classified those gusts at “Thunderstorm Wind Gusts” instead of the usual “non-thunderstorm gust”. I was driving down I-84 from Troutdale all the way to downtown when PDX hit 43. I didn’t see anything other than a breeze as I punched through the line of heavy showers. Maybe 25-30 gusts at most there. Due to the stronger gusts, PGE had almost 30,000 customers out of power in the early afternoon, then the number stayed under 2,000 customers through the rest of the breezy/windy evening and Monday. But a nice warm-up to the storm season ahead!

4. No waterspouts or tornadoes. The pattern behind the front Sunday afternoon was quite similar to October 2016, which produced several waterspouts and a tornado along the coast. I didn’t see any waterspout pics or videos. NWS saw rotation several times after dark Sunday evening. That was offshore Astoria to Long Beach. Maybe if it was daylight something would have been visible. But no reports this time around.


One “Bomb Cyclone” Down, One to Go!

October 21, 2021

10pm Thursday…

After a very warm day with some lower 70s in the metro area, moderate to heavy rain has arrived with a Pacific weather system. I expect steady rain for a few more hours, then the usual scattered showers behind the front the rest of tonight. Expect more showers Friday but decreasing as the day goes on.

TWO IMPORTANT NOTES

  1. You may hear/see something about a powerful storm (or worst ever?) for the Pacific Northwest this weekend. No, there is not a mega-storm on the way for the region. THERE WILL BE A HUGE STORM OFFSHORE, but it’s far enough away that we get typical wind/rain. No big storm.
  2. Things are moving fast/furious now with a strong Pacific jet stream overhead, so weather will be changing quickly from day to day…make sure you are paying attention to forecasts.

Tonight’s front is the leftovers of a powerful “Bomb Cyclone” that moved through the northeast Pacific ocean well west of the Pacific Northwest. A bomb cyclone is simply an area of low pressure that deepens “explosively” in a short period of time. Anything over a 24 millibar drop in 24 hours is considered a “meteorological bomb cyclone”.  No, it’s not a made-up media phrase.  Meteorologists have been watching these storms develop in the north Pacific/Atlantic for decades and that’s the term we’ve always used.  Somehow national media stumbled upon the term a few winters back and decided it was appropriate for the public to hear.  Generally (for good reason) I have kept the word “bomb” out of my on-air forecasts, but apparently it’s okay now and I sure used it last night! So that first cyclone is now weakening after bottoming out at around 950 millibars well west of the 130W “danger zone”. When deep low pressure centers track through this area we watch very closely!

Our big windstorms west of the Cascades almost always occur when a low pressure center tracks within this area

Now this is amazing; we have a second (and stronger!) bomb cyclone developing Saturday night and Sunday. Yep, that’s two huge storms relatively close to the region in less than 4 days. Highly unusual.

The latest global model forecasts are in remarkable agreement this evening. All are forecasting a surface low pressure center to drop from around 993 millibars Saturday morning to 943, yes 943, millibars. You can see the track of both lows, notice this 2nd one will be a bit closer

That 943 millibar value will probably be an all-time record deep low pressure so close to the region. For comparison, the Columbus Day Storm was “only” around 960 mb, but less than 50 miles off the coastline! Tracks of the last three major regional windstorms…all well inside 130W.

Ryan Maue, a meteorologist with www.weathermodels.com, checked lowest surface pressure in the 1950-2021 record. He tweeted “the minimum central pressure of 944 millibars from next storm off Pacific Northwest coast will likely be the deepest/most intense in this area of ocean at 45°N and 135°W at least since 1950” The graphic he tweeted shows that boxed area. Plus you see the lowest pressure right up against our coastline (the past 70 years) was that 960mb during the Columbus Day Storm.

This is all interesting stuff of course, but what’s the effect along the coastline and interior? A gusty east wind Sunday morning turns breezy from the south Sunday afternoon and Monday. Yet the strong wind field remains offshore through the event.

The ECMWF model shows this well, gusts over 100 mph over the open ocean, but under 70 mph along the Oregon coastline. This shows accumulated gusts (highest gust) from now through 5pm Sunday.

Most likely we’ll see gusts 55-65 mph along the beaches and 30-40 in the valleys. That’s relatively weak of course, not a windstorm, but enough to make for a windy Sunday afternoon!

That’s it for now, I’ll be off tomorrow but back at work Saturday and Sunday tracking our very wet weather pattern.

Chief Meteorologist Mark Nelsen


Enjoy Tuesday’s Sunshine! Rainy Season Arrives Late Week

October 18, 2021

8pm Monday…

October has been a cool but somewhat “dry-ish” month so far in Oregon and SW Washington. Just under an inch of rain in Portland and far less in Eastern Oregon. But we still have 13 days to go this month and a lot can change the 2nd half of October. The PACNW rainy season often arrives during this last half of October and it appears that WILL be the case this year.

First, enjoy your Tuesday because we have a spectacular day on tap. Offshore (easterly) surface flow plus just a few high clouds should allow temperatures to “soar” into the mid-upper 60s. We are in “peak color” in the metro area, so the combo of sunshine and yellows/oranges/reds shouldn’t disappoint. This will be the last guaranteed dry day.

A cool upper-level trough swings through tomorrow night and early Wednesday along with an associated weak front. Expect a bit of rain during this time, but less than 1/4″. Things get more interesting Wednesday/Thursday as a “bomb cyclone” develops out in the Eastern Pacific. A bomb cyclone is a rapidly deepening area of low pressure that deepens more than 24 millibars in 24 hours. This happens several times each cool season in the Pacific, but this one is a bit closer to our region. Who can forget the Thanksgiving Week bomb cyclone that slammed into SW Oregon and N. California two years ago? That one dropped about 40 millibars in 24 hours; similar forecast with this one. Enjoy the memories of closed highways and damaging wind here: https://fox12weather.wordpress.com/2019/11/24/a-bomb-cyclone-southern-oregon-snow-storm-coldest-thanksgiving-weekend-in-years/

Here’s the 11pm Tuesday forecast from the ECWMF (European) model showing a developing low north of Hawaii. About 998 millibar central pressure. Surface pressure is the line contours, colors are upper level heights

Then just 24 hours later…11pm Wednesday. A 954 mb low about 600 miles west of the Oregon coastline. That’s a 42 millibar drop in 24 hours. This is similar to the Columbus Day Storm low pressure center. Except that storm shot south to north quickly up the coastline just 50 miles offshore!

As you may suspect, a storm of this magnitude produces strong wind and a large wind field. This graphic shows the highest wind gust forecast between now and Thursday afternoon. Some gusts around 90 mph over the open ocean, but it’s so far away that gusts 30-50 mph are the most we can expect along the Oregon coast.

Beyond this big storm offshore, a strong westerly jet sets up Saturday through much of next week. It aims first at California, then shifts a bit farther north next week.

This should give round after round of valley rain and mountain snows. This can be a pattern that leads to a windstorm. That’s IF a surface low develops on the north side of the jet and IF it comes up the coastline just right. Here’s a neat tool that allows me to quickly look at all ensemble members from one model. Each colored box and number is a peak gust for the preceding 6 hour period. Each horizontal line is one of the 30 GFS ensemble members. A quick glance shows not too many greens/yellows/reds, but there are a few. As we get closer to a possible event I would expect more to show up in a vertical line, like the gusty southerly wind that shows up midday Wednesday. Of course this is for Portland.

How much rain is ahead? Quite a bit. I see 2-4″ in the next 10 days. Just through next Monday, the ECMWF gives us about 2″ in the western valleys

And fire season will be ending very soon in the northern half of California. 5-10″ in the mountains down there during the same time period

KEY POINTS

  • Tomorrow is your last guaranteed dry day for quite awhile, for at least a week
  • Rain showers both Wednesday and Thursday will not be heavy, although it’ll be breezy Wednesday
  • A very wet weather regime arrives Friday and continues through next week, plan on a wet weekend, but there will be breaks in the rain, not all-day long soakers.
  • At this point I don’t see a windstorm or flooding setup, but will be watching closely since this is the right pattern for something to develop

Chief Meteorologist Mark Nelsen


Chilly October = Pass Elevation Snow & First Frost In Lowlands

October 10, 2021

9pm Sunday…

We’ve all noticed the change. After 6 months of warmer than normal temperatures, October is running well below normal temperature-wise. For the first 10 days. During the last 10 days of September we saw 3 days in the 80s in Portland; it’s hard to believe that less than three weeks ago we saw highs around 90 in the metro area! Of course it’s normal to see temperatures drop off in October; no other month changes as dramatically in the Portland area. But going from above normal temps to below normal has accentuated that change this year. You can see that we are a bit alone in the Pacific Northwest, the rest of the country has seen a very warm start to fall.

The coldest airmass of the season so far has arrived this evening behind last night’s cold front. For the first time since spring, it’s snowing hard and sticking at Government Camp

Sticking snow should fall about 1,000′ lower than this elevation, down to around 3,000′ by sunrise. I expect 1-2″ at Govy and 3-5″ higher up at Timberline (6,000′). We’re in a showery airmass that dries out by sunrise, thus not expecting a ton of snow.

The reason it’s been cool? A weather pattern we saw this past spring; not especially wet, but cool. Take a look at the current 500mb heights and the anomaly (blue colors). Well below normal for October 10th as a cool trough or “dip” in the jet stream is passing overhead

A warm/strong upper-level ridge is out in the eastern Pacific and COULD move over us the next few days. But instead another cool trough flattens that ridge, and drops right into the Pacific Northwest late Tuesday and Wednesday. That’s another round of (light) rain and (light) mountain snow. Models say the following few troughs coming eastward on the jet stream will dig farther west; putting us in a milder southwesterly flow late this week and beyond. Wednesday the 20th…

So temperatures may turn a bit warmer the end of this week and beyond. As for rain, I don’t see a tremendously wet pattern over the next week, just showery at times. The same ECMWF ensembles show the near to below normal precipitation the next 7 days (brown = drier than average)

Then significantly wetter NEXT week; northern/central California may get its first soaking since late last winter

By the way, October 2019 was very cool and a bit dry. So there’s no reason to think that a cool October leads to a cool winter. Winter 2019-20 was mild & boring (no snow/ice/windstorms) with only a dusting of snow in mid-March in the lowlands.

Tomorrow night we get lower relative humidity, clear sky, calm wind, & a leftover cool airmass. That combo SHOULD give us the first frost in some outlying areas. No, not a big “pipe-busting” overnight freeze, just cold enough to end the growing season in spots. I’m going 36 in the city, which means some upper 20s in the coldest outlying areas. The NWS has just issued a Freeze Watch for tomorrow night for this reason for many areas west of the Cascades.

That’s it for now, I won’t be posting as regularly since I’ve been busier and we’re short two weather people. I’ll try to get it done once per week and more often if something dramatic happens.

Within the next two weeks I’ll get my winter thoughts together as well. We know it’s La Niña and a cold PDO this season. Hmmm…we will see.

Chief Meteorologist Mark Nelsen