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


Dry October Start & Goodbye to Brian MacMillan!

September 30, 2021

5:30pm Thursday…

It’s been a bit wet at times today, but not exactly a big soaker. This wraps up the month of September AND the “water year”. We use “water years” because we want to put all of each wet season into one “bucket” for historical purposes. Since each wet season in our climate begins Oct/Nov and ends in April, meteorologists across the Western USA have created a “water year”…precipitation from October 1st to September 30th. We will end up with just over 30” this year; the number below will end up a bit higher after the showers today…

Notice we’ve had 4 dry years (lots of drought in Oregon) after two very wet years. Hopefully this winter we can get more rain/snow to recharge groundwater and fill reservoirs. More on that in a later post about the upcoming winter. It’s obvious we have a nice start to October. Both Friday and Saturday will be dry with warming temperatures. Anything above 70 is now considered warm…things change quickly this time of year.

But let’s get on to the big story…

Brian MacMillan is moving on…yes, Brian is leaving KPTV/KPDX here in Portland

After 12 years, my best “weather buddy” is leaving us. No, no one did or said anything offensive or illegal. He’s not getting fired, laid off, and probably won’t leave tire marks in the station lawn on the way out. Nothing like that. Brian has accepted a new position with…wait for it…FOX…13, not 12, in Seattle. I grew up in Chehalis, so I regularly watched Q-13 (KCPQ), just like Brian did since he grew up in the northern suburbs of Seattle. They are making some changes and one is the retirement of longtime morning weather anchor MJ McDermott. So Brian is taking over her morning shift in his “hometown”. It’s a great opportunity for him, but I’m really going to miss that guy!

Brian came here from Bend in 2009 with just a couple years of TV under his belt. Just a young guy with no obligations. During that time he got married, bought a house, and now has two kids. He’s blossomed into a solid meteorologist and reporter that we will miss. The old saying of “jack of all trades, master of none” doesn’t apply to him. He’s really good at just about everything and a solid professional. EVERYTIME I (or a boss) asked him to fill a role, he did it without complaining.

We just finished a brand new FOX12 WEATHER PODCAST (episode #30) and Brian talks about all the different roles/responsibilities he held here at KPTV. We had some great laughs as he went over 12 years of memories and crazy stories. I think this podcast is my favorite of dozens we’ve produced.

Find it on your Apple Podcasts or just go to this link: https://www.kptv.com/podcasts/weather/

One of my favorite memories is Brian (trying) to take a drink up at Women’s Forum viewpoint during a raging easterly wind…now THAT was good TV!

And he could have been a window washer! Luckily the ropes held for this story…

We were recording something at one point and BMAC just jumped at the chance to spray me down. We were aiming for that “sweaty” look, but putting diet coke in a some fancy wine glass just didn’t work out quite right…

And who fills out THIS MANY vacation requests all at once???

I once walked in to this pile of his requests; I left the pile and added the large red DENIED sign. We’ve had a lot of fun!

All those tornadoes? From Aumsville to Manzanita to Longview, we worked them together. I’m really going to miss Brian’s forecasting skills too. I’ll come in during a snow/ice event (or in the lead up to one) or we’ll have a conversation about the meteorology as we compare notes. We almost always have the same forecast, even in those tough winter weather setups.

And of course most of all I’ll miss Brian’s friendship here at work. We’ve shared the ups/downs of family life, (a couple) crazy coworkers, training new employees, conversations about COVID, riots, elections, deck staining, roof replacement, strawberry varieties, ties, suits, music, etc… You only see us for a few minutes at a time on TV, but remember we work together for 8 hours each day behind the scenes just like “regular” office folks. Brian is the nicest guy, always positive, and always asks his coworkers “how things are going”. I’ve learned a lot from him! Luckily, we’ll only be three hours apart via freeway…not too far away. Always time for a little Seattle vs. Portland gossip right?

So… to wrap it up, we’re losing a great employee but in a good way I suppose. New experiences are one of the best parts of life.

Good Luck Brian!

Chief Meteorologist Mark Nelsen


EF-0 Tornado Hits Battle Ground Monday

September 28, 2021

7pm Tuesday…

A couple times each year we get a (usually) weak tornado in our viewing area. That’s SW Washington down into NW Oregon and east into most of Eastern Oregon. They may be uncommon, but definitely not unusual.

Back in March a weak tornado touched down near the mouth of the Columbia River, close to Ilwaco. That was an EF-0. Last night a strong thunderstorm tracked through central Clark County. As it passed west of Battle Ground and then ENE to Yacolt, radar indicated some decent shear/rotation. The NWS issued a severe thunderstorm warning around 7:30pm, just as a tornado finished tracking through the area. Here’s the view at 7:35pm

Soon after I heard from Tyler Mode, an avid weather “geek” and photographer from Battle Ground. He was watching the storm and recorded video of a tornado passing just north of the city. Check out his video…especially around the 1:10 mark: https://www.tylermodemedia.com/Weather/92721-Tornado-Battle-Ground/i-tKsZzwz Pretty exciting! Listen closely for the roar in the distance.

Shorty after seeing Tyler’s video, we received a great view from Gary Gerber. This video really shows the circulation, wind in the trees, and debris in the air. It doesn’t get much better than that in our area.

Once we saw these two videos it was obvious a tornado had touched down. The Portland NWS went out and did a storm survey today. Surprise! It was ANOTHER EF-0. This is from the NWS report

Every tornado in our viewing area the past three years has been rated an EF-0. Note there have been no tornadoes so far this year in Oregon.

But we still have three months to go! And autumn has been a good time for tornadoes in our area. It’s interesting that mid-winter and mid-summer have the lowest chance of tornadoes; probably because we don’t get many showery patterns in July/August. And in mid-winter the showers are weaker and thunder is more rare for inland areas.

Of course most of these tornadoes are weak. The vast majority the past 70 years have been in the EF-0 and EF-1 categories.

I often get two key questions about tornadoes:

Are there more tornadoes in the region than we used to see? Becoming more common?

The short answer is NO. Remember that 30 years ago almost no one was walking around with a camera attached to his/her hand (constantly). Now EVERYONE has a high quality camera just a second away from use. Think about it; there’s a good chance that in pre-internet times, the storm in Battle Ground wouldn’t have been noticed except by a few homeowners wondering why part of the tree is across their lawn. And how many of them would have taken the time to call the Portland NWS office? There’s a reason that almost all reported tornadoes in the PACNW have been in populated areas. And the actual reported numbers have not increased dramatically either.

Is there some reason Clark County seems to attract tornadoes? A new “Tornado Alley”?

YES & NO. We have seen a couple of significant tornadoes in Vancouver (2008) and Battle Ground (2015) the past 20+ years. Those two were the most destructive. Other weaker tornadoes touched down in Salmon Creek (2017), Orchards (2017), east of Battle Ground (2013). The only deadly tornado on record in the Pacific Northwest was the F-3 that tore through Vancouver in April 1972, killing 6. A great study by Dave Elson at Portland NWS found that horizontal rolling of the southwesterly flow coming off the Tualatin Mountains (West Hills) may contribute to increased frequency downwind of that NW to SE topographic barrier as you can see in this image.

You can find his presentation here: https://www.ametsoc.org/chapters/oregon_archive/Minutes/2008/2008_11_20_Minutes_Powerpoint1.pdf

But no, there’s no new “tornado alley” developing in our area.

That’s it for now. Enjoy the (mainly) dry weather Wednesday. After more showers Thursday, October starts with 4-5 dry days.

Chief Meteorologist Mark Nelsen


Rain Is Back This Evening As A “Wet” September Wraps Up

September 26, 2021

9pm Sunday…

I was on vacation and missed the big downpours last weekend so I’m happy to see my first rain of the season tonight. I took a much-delayed “Graduation 2020” trip from New York City to Washington (DC), then down to very sweaty/hot Florida with part of the family. It was soooooo nice to fly back into PDX on a clear evening late last week and feel the low humidity. It’s not perfect, but we live in a nice climate don’t we? Of course it’s “pics or it didn’t happen” nowadays, so here you go

Alright, moving on to the rain…models were right on showing a nice day today followed by light evening rain. We hit 75 in Portland today, down about 10 degrees from the very warm mid 80s yesterday. Notice the 60s up in Puget Sound with showers off/on all day

We may not have broken the all-time record for 90 degree days, but Portland has never seen so many 85+ or 80+ degree days. Yesterday was the 90th day at/above 80, a new record

Radar shows one band of rain moving through the I-5 corridor right now and another offshore. That should arrive around 2-4am. This is the leading edge of a cool upper-level trough. It swings through the region Monday night and Tuesday. It’s a pool of cool air dipping south, you can see the lower-than-normal heights (cool colors) on the Monday night 500mb map

Then by Thursday the trough is gone, replaced by weak high pressure and higher than normal heights (warmer colors)

So we have two days of the usual spring/fall showers and sunbreaks pattern. Those are the days when we get sunbreaks, then a downpour 10 minutes later, then sun pops out for 30 minutes, repeat… This is also the setup (Monday and Tuesday) for scattered thunder/hail showers too. I noticed Lifted Index (a measure of instability in the atmosphere) is around zero or below both days along with CAPE up a bit too. A pretty obvious signal for isolated thunderstorms in our climate west of the Cascades. During the event last weekend some areas picked up 3-4″ of rain! This time it’ll be more like 1-2″ in the wetter parts of the metro area near the Cascades, and .50-1.00″ in the lowest elevations. Unfortunately with westerly flow you won’t see much in the lee of the Cascades. Less than one tenth of an inch for some of you in Central and north-central Oregon. The GRAF model gives us these numbers for rain by Tuesday night

Notice the Cascades and Coast Range could get 2″ or so in the wetter locations.

Portland has experienced quite a few “wet” Septembers lately; six consecutive years. Actually two of them were close to normal. Most often the rain has fallen in the 2nd half of the month like it did this year.

And you can see PDX and northern parts of the metro area are running well above the Willamette Valley totals for September rain due to the downpours early Sunday morning last week

Last weekend’s rain put fire season on life support. This rain event will put the “nail in the coffin” for sure. Even after six days of dry and warm weather, those Cascade fires were barely putting out any smoke yesterday/today and we’ve seen almost no increase in acreage burned. This event will finish things off. About 200,000 acres have burned in the Oregon Cascades this summer! Much of it started from those thunderstorms that moved north along the mountains the last few days of July and August 1st-3rd.

Are we entering a days/weeks long rainy period? I don’t think so. We’ll be dry Wednesday, then a weak warm front gives us sprinkles/showers Thursday. By next weekend, heights are rising and the early fall jet stream has been pushed far to the north again. It’s possible we have a very warm first weekend of October on tap.

The ECMWF 24 hour precipitation ensemble chart shows good agreement on dry (circled) Friday through Monday, then possibly some showers return next week at some point. Both GFS and GEM models are similar. This is about as normal as it gets for early October. A little wet, then dry, then a bit of wet again…

SUMMARY

  1. Some nice wetting rain falls the next two days, probably up to 1″ in valleys and 2″ or so in Cascades
  2. Mainly dry Wednesday through NEXT Monday except for some light showers Thursday
  3. A mix of sun and clouds is likely Wednesday and beyond.
  4. Temperatures average near normal the next 7-10 days
  5. I’ve been waiting for a cool/wet day to clean my garage and workshop…it’s time.

Chief Meteorologist Mark Nelsen


Weekend Rain Slow To Arrive = Drier & Warm Friday

September 15, 2021

8pm Wednesday…

I’ll be on vacation and out of town Thursday through most of next week, so here’s a quick update. It’s too bad I’ll miss the first soaking of fall this weekend!

Here’s the plan:

  • The next two days (Thursday/Friday) will be all or mainly dry from Portland south and east. Temperatures warm into the upper 70s the next two days too. There COULD be a sprinkles or a light shower during the daytime Friday, but that’s it.
  • Real rain, “the soaking”, doesn’t begin until sometime after sunset Friday evening. At this point it appears high school football games could be dry; or at least you shouldn’t see any downpours
  • The bulk of heavy rain (about 1/2″ in western valleys), falls Friday night through early Saturday morning.
  • Showers continue off and on Saturday, although they may not be very intense. Expect the usual downpours, then sunbreaks, then a rumble of thunder etc…
  • Sunday appears to be the wetter of the two days this weekend. More frequent and intense showers are likely. This can be the setup where we get funnel clouds too.
  • It’s back to warm and dry weather most or all of next work week. This is a “one-shot” deal, not the beginning of a cool and wet period.

In general, weather forecast models have been in good agreement on the wet pattern this weekend. A cool and broad upper-level trough settles over the Pacific Northwest late Friday through Monday. You see the much lower than normal heights (around 18,000′ up in atmosphere) midday Sunday.

Ahead of that cool trough, a wet Pacific frontal system first aims at Washington state on Friday. This is the change the past 24 hours. Originally models were thinking the system would be farther south to start. But now it’s obvious just about all rain remains in Washington on Friday. THEN, Friday night and Saturday it slides south through Oregon. In the end our total rainfall is still the same mentioned (previous blog post) a few days ago; about 1″ or so in the western valleys by the time we dry out Monday. This is the morning ECMWF model. It’s interesting that both GFS and ECMWF ensembles show about 1.5″…good agreement.

And you see the widespread 2-3″ in the Coast and Cascade ranges. This will put Fire Season 2021 partially into the grave. There won’t be much left of those fire complexes burning on the west slope of the Cascades.

Sunday’s snow level (the lowest elevation we’ll see sticking snow) in the Cascades is close to Timberline Lodge…could be a mix there, or even a dusting by Monday morning. But of course it’s too early and too warm for pass elevation snow.

After a few leftover (light) showers Monday, it’s back to mainly or all dry weather next week.

I see about 1/2 of the European’s model ensembles generate measurable rain again AFTER this weekend in the last week of the month. But 1/2 do not. It would be perfectly normal to see a round of showers again in the last week of the month. That said, my gut feeling is that the last week of September will be much improved from this coming weekend!

Enjoy the rain this weekend! After 3 months of dry weather, FOLLOWING the driest spring on record, we desperately need it. I will be back at work that last weekend of the month.

Chief Meteorologist Mark Nelsen


Good News…Rain Is On The Way!

September 12, 2021

9pm Sunday…

What a nice early fall weekend; partly cloudy (& dry) sky plus comfortable temperatures. I drove through a couple spots of drizzle midday on the way to work, but it was not measurable. Yesterday we were a few notches above average; today a few below.

The next two days will be similar with more sunshine than cloud cover. Wednesday a weak/dying cold front moves overhead. The main result will be cloudier skies (like today) PLUS spots of morning drizzle or a shower. Thursday should be uneventful as well. So other than a shower/drizzle chance Wednesday morning, not much happens through Thursday and your life will be un-affected by any real weather. Then on Friday things change…rain arrives (yes, real rain) and we may have 4 wet days on tap.

HIGHLIGHTS

  • The endless dry days we’ve seen for 3 months (since mid-June) come to an end this coming weekend
  • Expect whatever you have outside to get soaked Friday through NEXT Monday…around 1.00″ rain in the lowlands
  • This won’t help the drought much, but at least the top layer of soil will finally moisten up
  • All Cascade wildfires will see chilly temps, high humidity, and a good soaking.
  • After next weekend, Fire Season 2021 will be on life-support over/west of the Cascades; we are going to avoid a long episode of smoke and huge fires west of the Cascades this year. A good ending considering how bad things were looking by late June (drought + driest spring + extreme heat). A lack of lightning for most of August plus a cooldown late that month was a game changer.

The reason for a cooler/wet forecast next weekend?

Our first strong upper-level trough of the season. That means a significant dip in the strengthening early fall jet stream. Cool air pushing farther south than it has the past few months, spinning up several disturbances on the boundary with the warmer air. You can see the relatively flat flow now…no hot ridge of high pressure nearby

But check out next weekend. Our typical wet/cool weather pattern in both spring and fall

How confident am I that this is a real pattern change? Just one example…ALL of the 12z ECMWF 24 hour precipitation ensemble members produce some sort of significant rain Friday-Monday. That’s unusually high confidence. If only half of them were showing this I’d be a bit more skeptical. Also notice about half of these members bring in more rain as we head toward the end of September

Ensemble forecast temps also show we are headed into cooler weather

How much rain? The operational high resolution runs of the GEM, ECMWF, & GFS produce anywhere from 0.70″ to 1.20″ during this time in the western valleys (Portland, Vancouver, Salem). In this case it’s better to use the averages from the ensembles…which are in good agreement… Somewhere around 1.00″ or so in the lowlands of NW Oregon and SW Washington. Not a drought-buster, but enough to moisten things up quite a bit

You’ll notice in the comments above I’m quite optimistic about putting this fire season partially to rest. That’s because those ensembles also push 2-3″ rainfall into the Cascades, right over those 5 fires burning from north of Detroit down to east of Grants Pass. That’s enough to eliminate most smoke from those fires. That’s why I’m feeling good about that last few weeks of this fire season. Last year just under 2 million acres burned on the Oregon and Washington landscape. About a million of that was in the one week after Labor Day (easterly windstorm leading to mega-fires). So far we’re at about 1.4 million this year. We will likely end up with less acreage burned this year, even with a hotter summer and much drier spring conditions. By the way, last year on this date we were in the middle of that incredible 8-11 day stretch (depending on location) that featured the worst air quality we had ever seen in NW Oregon and SW Washington. Here are the numbers that we will be avoiding this year

That’s it for now, I just wanted to give a heads up about the wet weather arriving later in the week. I’ll plan on another blog post midweek with an update. Chief Meteorologist Mark Nelsen