April Begins Warm & Dry

April 1, 2021

9:30pm Thursday…

It was another fantastic spring day across the region wasn’t it? Just a few thin high clouds drifting lazily by at times. We made it to 68 in Portland, just a few notches down from the 71 yesterday (March 31st). Salem and Eugene were a bit warmer than yesterday.

March Recap

In my opinion, we’ve had a great start to spring if you like to get outdoors. March was drier than average, with plenty of partly cloudy or sunny days. It was our 7th driest on record at PDX (out of 81), and the 2nd driest during a La Niña winter/spring.

Just as interesting? We’ve now gone through four consecutive years with drier than normal conditions in March. Payback will be a real tough in some future March!

And you can see most of the West has been quite dry this past month

What about temperatures? A bit cooler than average. Not a huge departure, but most of Oregon has been cooler than normal.

Is this unusual? Not really. Looking back at past La Nina springs, there is a very strong signal for cooler than normal across the Pacific Northwest. This is a composite of April-June temperatures for the last 20 La Nina springs. Pretty clear signal isn’t it?

One would think a cool spring would also be wet, but that’s not the case. April through June precipitation from those same 20 springs…well below average.

I don’t mind these springs too much; plenty of sunny or partly cloudy days mixed in with the wet days. Plenty of chilly nights and late frosts (like this year), but a cold/clear night is followed by very strong April/May sunshine too!

Snowpack is still running well ahead of average in northern Oregon; no significant spring melt yet due to the cooler temps. Southern Oregon is not in good shape as of April 1st. Lots of drought issues are likely across the Klamath and Good Lake basins

What’s Ahead?

April is what I call the “greening up” month west of the Cascades. Most deciduous shrubs and trees come alive this month; bare of foliage to start, then flush with fresh leaves & green by April 30th. It’s very dramatic in the woods around my home. Right now the ground is pretty much bare and bright sunshine makes it down to the forest floor. But four weeks from now all the ferns will have popped out of the ground, alder/maple trees will be leafed out. It turns darker and shady in the woods from that point through October.

Portland’s average high temperature rises from 59 > 64, and we typically see 5 days at/above 70 degrees. Last year we made it to 76 degrees late in the month

We have also entered the drier half of the year…just barely. April is slightly drier than October in a typical year as the rainy season slowly winds down

In the short term, we’ve got a dying cold front that brings a few sprinkles to the northern Oregon coastline tomorrow. Then (unfortunately) on Easter a splitting upper-level trough brings another dying front overhead. Lots of clouds that day but not much rain! The fresh 00z GRAF model shows how little rain we expect through Sunday afternoon. If there is no color on this map, that means less than 0.10″ precipitation.

The result? Not much rain and temperatures near normal for this first week of April. And…

EASTER WILL NOT BE A WASHOUT, JUST LOTS OF CLOUDS PLUS A FEW SPRINKLES OR A SHOWER

Chief Meteorologist Mark Nelsen


Powerful Spring Cold Front Plowing Through Oregon This Evening

March 28, 2021

9:45pm…

This afternoon/evening we’ve seen a classic spring cold front pass through the region. Ahead of the front, in the warm airmass, temperatures soared into the 60s & 70s east of the Cascades. Ontario even hit 82!

But with the clouds and afternoon rain we didn’t make it much above 50 west of the mountains

Meanwhile, Government Camp hit 50 degrees at noon, but now it’s SNOWING and 24 degrees! Now that’s what we call a cold front kids…

The front is a dividing line between a warm spring airmass and a much colder airmass that’s pouring inland now. Snow levels have dipped to around 1,000′ in the Coast Range. We’ve been mentioning for days that there could be a dusting of snow on the Coast Range summits Monday morning and that will be the case. But there isn’t a lot of moisture behind this system; it’s more like a “continental” cold front you’d see in the middle of the USA. Just some scattered showers tonight and Monday. In fact take a look at the evening GRAF model precipitation forecast. Very little between now and Wednesday…almost all of that before noon tomorrow.

But we should be able to get 8-12″ Cascade snowfall (including what we’ve seen so far) by the time it dries out later tomorrow.

There was a strong surge of southwest or westerly wind with the cold front west of the Cascades. Peak gust of 35 mph at PDX along with other gusts in the 25-40 mph range gave us quite a few power outages. I see PGE has about 5,000 customers out. Of course the wind has died down now.

Central and Eastern Oregon (along with eastern Columbia River Gorge) is sure known for gusty southwest or westerly wind in the spring, but today was well beyond anything we normally see. Peak gusts 50-70 mph were widespread. I saw a 75 mph gust at Maryhill, and even Pendleton saw a gust to 73 mph! Take a look at the blowing dust around Rufus earlier…from Sherman county sheriff

Warm weather, a dry March, and strong wind started at least two fires in the Bend area. One of those prompted Level 3 evacuations for at least a short time. There were at least 2 more in Wasco county as well.

What’s Ahead?

  • More drier than normal weather to wrap up March and begin April.
  • A few very light showers tomorrow, then warming Tuesday/Wednesday.
  • A combination of mostly sunny skies + offshore flow + warm airmass Wednesday COULD give us our first 70 of the year. Our evening GRAF model says 73! ECMWF implies a high around 70 as well. Then back to onshore flow and cooler temps (but still mild) April 1st.
  • Both GFS & ECMWF ensembles also imply the drier than normal conditions continue for at least another week.

So…the main message tonight? Make sure you schedule some outdoor time for Wednesday!

Chief Meteorologist Mark Nelsen


Spring Break, A Tornado, & Wet/Dry Parts of Metro Area

March 21, 2021

9:30pm Sunday…

Ahhh, spring break in Oregon. One thinks of…exactly what our 7 day forecast shows. A mix of cool, showery days plus some warm sunshine too.

It’s raining this evening as a cold front approaches the coastline.

The front should pass by Astoria by midnight, then through the metro area sometime between 2-4am. Behind this front the steady rain changes to our usual “sun & showers” spring weather pattern. Tomorrow won’t be all that wet, just light showers that come and go. Snow levels stay relatively low and I expect another 6-10″ snow around Mt. Hood above 3,000′. The snow level forecast based on the ECMWF model…

We get a break from the rain Tuesday, then another weak system moves inland Wednesday. That does give us a beautiful spring day Tuesday, but then it’s back to onshore flow and gloom Wednesday. Rain has been running below average this month, and we’re slowly making up a bit of ground. But it appears we’re headed back to drier weather again Thursday through next Sunday. See the upper-level ridging developing just offshore Thursday

Then it’s right over us next Saturday…could be well into the 60s with sunshine!

Then by NEXT Monday a cold trough drops in over us, crashing the warm/sunny party.

That should leave us with a bit of a dry spell. Most likely Thursday-Saturday, or possibly Thursday-Sunday. Or if we get leftover sprinkles Thursday, it would just be Friday-Sunday. The point is that you should be aiming for Friday/Saturday for guaranteed dry days. Thursday & Sunday will be bonus days if we can stay dry for those.

Hopefully no one missed the “big tornado” Friday evening? Portland NWS says a very weak EF-0 touched down very close to the Ilwaco airport. That’s near the mouth of the Columbia River NW of Astoria. 65 mph wind and damage could only be tracked for about 1/3 of a mile.

This is the latest in a series of very weak tornadoes in our area the past few years; all EF-0

On another subject, I spent almost two hours tonight “digitizing” a metro rainfall map.

Huh?

It goes back to Charlie Feris, a local Oregon AMS Member. Charlie worked at BPA as a meteorologist for many decades. During that time he set up a network of rain gauges around the Portland metro area. People would send in monthly rain totals and he would tabulate the numbers. I believe Charlie retired in the early 2000s but he has continued to “accumulate” the monthly rain readings. Over the years he has created a contoured map, showing annual average rainfall in our area. I remember first seeing this 20+ years ago. Then last March, at our last in-person AMS meeting, he passed out some copies. I told him I’d love to get it in graphical form so it’s saved for future use. That’s what I did this evening. Here’s the original version:

And (a very colorful) TV version…

Let’s talk about it. I don’t think many people are aware how much variation we get in annual rainfall here. A few points:

  1. In general it’s driest in the lowest elevations and wettest higher up. That makes sense because as clouds rise over terrain, they cool, moisture condenses, and raindrops form.
  2. There is a bit of a rain shadow coming off the Coast Range, possible off Chehalem Mtn. in southerly flow as well.
  3. The driest parts of the metro area are around Bethany and Tanasbourne areas westside, and Sauvie Island to I-205 bridge along the Columbia River. Some of these areas see less than 38″ in an average year. In fact the 30 year average at PDX is around 36-37″.
  4. Wettest (by far!) is the west slope of the Cascades. The eastern suburbs of Portland into the Cascade foothills pick up 50-60″ rain each year.
  5. Terrain has a huge influence not only on daily weather, but yearly precipitation.

Of course these numbers are averaged over a year. In certain patterns the variations on these maps can erased, or even enhanced. For example a strong westerly flow at 3-5,000′ can leave an inch of rain at Troutdale or Corbett, but almost nothing falls in Hillsboro. OR, a strong south-southeast flow in the first few thousand feet of the atmosphere can really soak the west metro (Banks, North Plains, Hillsboro), but leave those usually wet eastern suburbs significantly drier.

Alright, that’s it for now. Keep your fingers crossed for some warm sunshine at the end of the week.

Chief Meteorologist Mark Nelsen


Dry March Weather Ends, & AMS Winter Recap Meeting is Tomorrow

March 17, 2021

10pm Wednesday…

It sure has been nice this month so far! It’s St. Patrick’s Day, and we’ve picked up less than 1/2″ rain in Portland in the first 17 days of the month. We haven’t seen things this dry in the first half of the month since 2005.

Of course we all know things could change dramatically rain-wise in the next two weeks, but I see less than 1″ rain in the next week. March 2020 was the third consecutive year with drier than normal conditions. I suppose that made up for the March 2017 soaker.

We’ve been living a bit “continental” west of the Cascades the last few days. Cold/frosty nights, but warm afternoons. Today we hit 62 in Portland; much nicer than the cool/sunny/showery day Monday.

This month is running near average across NW Oregon and SW Washington, and I think we’ll be near normal over the next week. Expect cooler days, but much warmer nights with cloud cover and southerly breezes.

A cold upper-level low offshore moves inland the next three days

Expect three days of cooling and showery conditions. By Saturday the sticking snow level is back down around 2,000′, but I don’t expect a massive snowfall in the mountains. About a foot of powder from tomorrow through early next week.

So, we’re back to typical March showers and cool-ish weather for at least a few days


OREGON AMS WINTER RECAP MEETING IS TOMORROW!

Tomorrow it’s time for the annual winter recap meeting…and ALL OF YOU are invited. This is put on by our local American Meteorology Society (Oregon Chapter). Typically we meet at a restaurant, but due to COVID all our meetings this year are online. At one point (early February) I figured this would be a very short meeting, but of course the snow/ice decided to show up for a few days mid-month and now I have plenty of content. If you are into weather, this one is for you!

WHEN:

7pm Thursday, March 18th

WHERE:

Live video on Facebook, but YOU DO NOT NEED TO HAVE AN ACCOUNT TO WATCH ON FACEBOOK!

Link is here: https://www.facebook.com/OregonAMS/

The presentation will be available afterward at the chapter website: https://oregonams.wordpress.com/

It takes awhile to put it all together, but I’m finally finished. Here are just two slides to whet your meteorological appetite:

So feel free to hop on to the link and watch for awhile, or all, between 7-8pm tomorrow evening.

Chief Meteorologist Mark Nelsen


Two More Warm & Sunny Days; A Mild & Dry-ish March so Far

March 11, 2021

10pm Thursday…

Today was another fantastic early spring day. Other than patchy morning clouds, we saw sunny skies and warmer temps across much of the region. In fact the 61 degree high today in Portland was the warmest so far this season.

Tomorrow and Saturday should be similar, with Saturday likely the warmest day due to a warming airmass. Then a cold front moves inland Sunday midday, bringing a much cooler and wet day. So clearly SATURDAY IS THE “OUTDOOR” DAY THIS WEEKEND.

If we get up to around 64-65, that sure wouldn’t be a record, those are around 70 or so this time of year. How warm do we get in March? Most years we get into the upper 60s or lower 70s at least once by the end of the month.

March has been drier than average…

Temperatures have been near normal across the state, a little cool west and warm east.

The temps we have been seeing are about as normal as it gets for the first 1/3 of the month. The green on the chart below is typical temperature range (highs & lows). Red is record high for each day and blue shows record lows.

What a strange “La Niña winter” this has been. Except for 2-3 weeks in mid-late February, the entire cold season has been quite mild. We’re clearly out of winter weather now…EXCEPT for the cold showers behind Sunday’s system. Snow levels could dip down to around 1,000′ late Sunday night and Monday morning…maybe. 850mb temps dip down to around -7 to -8, although models don’t show much precipitation. WRF-GFS snowfall forecast has a few inches in the Cascades, but none for the lowlands:

Next week we’ll see a mix of dry and wet; not really a long & drawn out cool/wet pattern. Looks like decent March weather to me!

We just recorded a fun FOX12WEATHER podcast this afternoon. By “we” I mean me plus the other 3 meteorologists here: Anne Campolongo, Jeff Forgeron, & Brian MacMillan. It’s full of informative and interesting weather tidbits, plus we answered some of your questions. And my coworkers say I’m being a bit “too controlling” with the forecast. Hmmm…

You can find it in Apple Podcasts or listen straight off the web at this link: https://www.kptv.com/podcasts/weather/

Enjoy the weekend; I’ll be back at work Sunday afternoon…

Chief Meteorologist Mark Nelsen


Cold Showers Today; But Lots of Dry Weather This Week

March 7, 2021

9pm Sunday…

It was quite a dramatic weather day for some of us. A classic post-frontal (behind a cold front) unstable airmass flowed into western Oregon and western Washington today. That gave us an early spring mix of hail, downpours, bright sunshine, and a few lightning strikes. At 3:15pm one thunderstorm was moving across the West Hills and our system detected a lightning strike around the Cedar Mill area.

Sure enough, a cedar tree was hit in the Cedar Mill neighborhood. Thanks to Alex for this pic

And thanks to all of you that sent in hail pics. Late this morning 1/2″ to 1″ deep hail fell around the Seaside to Astoria area on the northern Oregon coastline. This one is from Lauren Masak in that area.

We get these hefty showers in early-mid spring for a couple of reasons. 1) The upper atmosphere in our area reaches its coldest point in late February and March, lagging the surface temps. In Portland our average high temperature has climbed from the mid 40s to mid 50s since early January. Warming below (compared to wintertime) plus just as cold above means more rising motions = hefty showers. 2) Sun angle is climbing rapidly. We are getting as much energy from the sun now as we would in very early October. A few sunbreaks and the surface warms quickly. That leads to “warm” bubbles of air rising through the chilly atmosphere overhead.

A large upper-level low is sitting off the West Coast; it won’t move much the next two days. Most of the energy and rain is headed south of us into California.

That cold upper-low drifts south and dies over the Desert SW Wednesday and beyond, leaving high pressure to take over for at least a few days Thursday-Saturday. By Saturday the ECMWF looks like this…

Other than a weak system passing by NEXT Sunday, the ECMWF operational model is mainly dry for about a week starting Wednesday. Ensembles from the same model show many members with mainly dry weather during that time. In general it appears the first half of March will end up being significantly drier than average; quite a change from what we’ve seen since December.

The one chilly trough passing through a week from now has been forecast by the GFS recently to bring much colder air for a couple of days. But…it is the GFS and it’s been trying to do that for a couple weeks… Most recent runs just have typical mid-March snow showers down to 1,500′ or so. Not much ensemble support for snow to lowest elevations either. That said…it is interesting that next Sunday is one year from the day we saw a morning dusting to 2″ in the metro area.

So if you have outdoor plans this week, you sure won’t get soaked. But I’d aim for Thursday-Saturday for the best chance of totally dry weather.

This evening I started working on my winter recap presentation I do each year for the Oregon AMS. This year ANYONE can easily watch the meeting since it’ll be on Zoom and Facebook. It’s 7pm Thursday the 18th. If you’re a weather geek and want to immerse yourself in an hour of weather stats, maps, charts…this is your chance! A couple of initial thoughts:

  1. What a slow winter!…Until those four days in mid-February. I have almost nothing to talk about for November, December, & January. At least we had a wind event and snow close call that month.
  2. This was the warmest La Niña winter on record in Portland! Although the urban heat island likely has something to do with that number. We’ll see how the regional numbers look when they come out this week.
  3. We’ve now gone through 7 winters without a regional “arctic blast”. Winters have been easy on our gardens recently…only 24 in Portland this year.
  4. Portland has seen measurable snow now for 6 consecutive winters. 4 of those were “big” snow years, but in two it just barely happened. We are due for a ZERO year I suppose.

Chief Meteorologist Mark Nelsen


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