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


End of Summer, Another Dry Water Year, & Looking For Rain

September 7, 2021

9pm Tuesday…

Since I last posted, we’ve seen August give way to September. Labor Day Weekend has come and gone too, a nice “end to summer” with abundant sunshine but no hot weather.

Of course meteorologically we just finished summer which runs from June to August. In Portland, Summer 2021 was just barely edged out by a slightly hotter Summer 2015. By 0.1 degree! Basically it was tied with 2015 for hottest summer on record at PDX.

In Salem, Eugene, Medford, & Redmond it was the hottest on record. As I’ve mentioned many times, Salem’s climate record is excellent, going back to the late 1800s. This summer was a scorcher!

This was our 9th consecutive warm/hot summer; of course not all of those were “hot”. Last year is a good example, just a bit warmer than average. 2012 was the last time we had a “cool” summer, mainly due to a very cool June. But 2015, 2018, & 2021 have been blazing hot. Portland has seen (so far) 24 days at/above 90 degrees. That’s at the higher end, but we’ve seen more in 2015 and 2018.

Salem has seen 39 days that warm; a new all-time record there. Eugene also set a record…41 days at/above 90 degrees!

Of course the drought continues… Portland has only seen .05″ rain in just under 3 months. And the six month period from early March through early September is the 2nd driest six-month stretch on record. Summer & early fall 1987 were slightly drier.

This means we are seeing another very dry “water year”. By the way, a water year is a term used throughout the Western USA. Since most precipitation falls in the cold season (straddling two calendar years), it makes sense to look back at wet seasons separately, which means starting the “water year” on October 1st each year and ending September 30th. We’ve got three weeks left this year. Right now it’s the driest since the 2000-2001 drought year…in Portland. We haven’t seen a wet year since 2016-17. Of course we could easily pick up 2″ rain the 2nd half of September, but even then it would be a much drier than normal year. Typically we get about 36″ in Portland each year.

Do we have any rain ahead? Not really, at least nothing significant through mid-month. A weak system drops a few showers tonight, then mainly or all dry through at least next Tuesday/Wednesday. Take a look at the ECMWF ensemble forecast chart for the next two weeks. It shows 24 hour rainfall. Each thin horizontal line on upper part of chart shows one of the 51 ensemble members. Time goes from now (left) to two weeks out (right).

Notice almost no members produce .10″ or more through the middle of next week, instilling high confidence that we’ll be dry through the 15th. But you’ll also notice around the 18th or so a lot of ensemble members say we could actually see rain. I’m not saying this is the case, but every few Septembers we get a big soaking the 2nd half of the month. In fact 3 of the past 4 Septembers we’ve picked up at least 2″ rain during that time.

It would be wonderful (and mainly finish the fire season) if we could get 2″ of rain in valleys plus 4″ in mountains the last ten days of the month.

One more note, it’s also obvious that we’re making a turn toward more typical (cooler) September temperatures starting Thursday. The same morning ECMWF model ensembles show temperatures consistently in the 70-80 degree range the next 10+ days. Summer is over…but warm early fall weather is here for awhile longer

Chief Meteorologist Mark Nelsen


Cooler Weather Wraps Up a Hot & Dry Summer

August 29, 2021

9pm Sunday…

Hopefully you enjoyed this last weekend of August? It was quite a bit different than the cloudy/sprinkles stuff we saw last weekend. Portland hit 87 both days

A very interesting month…blazing hot first half, then near to below normal the 2nd half

At this moment, it’s still the hottest summer (June-August) in recorded history at PDX. BUT, it’s only slightly above Summer 2015. Add in two cool days (tomorrow and Tuesday), and I have a feeling it’ll be a tie for hottest summer in Portland. Salem’s records go back into the late 1800s and it’ll definitely end up as #1 hottest there.

The drought continues of course. The six months March-August are the driest on record at PDX, totally blowing away the previous years. Hard to believe we’ve seen less than 4″ of rain since the end of February!

I did check and find that is NOT the driest six months on record at PDX. There have been just a few other years in which May-October rainfall was less than 4″ as well. But we’ve never had a spring/summer dry combo like this.

LOOKING AHEAD

We are in a typical late summer or early fall weather pattern now. That means we don’t stay in long warm/hot periods but not much rain either. Forget the air conditioning…nights have been in the 40s/50s much of the past week and that continues. Weak ridging overhead gave us the warm weekend, now a cool trough drifts through southern B.C. the next 2-3 days. You can see the dip in the flow Tuesday up around 18,000′

That’s on top of a major marine push in progress. Already at 8:30pm much of the metro area has dropped into the upper 60s. The westerly flow is also pushing all fire smoke east; notice the plumes coming off Cascade fires this evening are all headed into the eastern half of the state. This is the most active I’ve seen those fires in quite a few days. More on fires in a minute

More onshore flow means highs only in the 70-75 degree range the next two days, but I don’t expect solid gray skies. Sun & clouds will mix.

Wednesday through Friday the trough moves east and atmosphere warms…we should be back in the 80s Thursday/Friday. It’s not a hot ridge of high pressure; no “heat dome”. Just an absence of any cool systems nearby. The Friday afternoon view

LABOR DAY WEEKEND

Models generally have some sort of upper-level trough swinging by around Sunday/Monday, but they are in great disagreement. Just taking a look at the ECMWF ensembles today, 21 of 51 members (a little under half) bring some real showers through Portland either Sunday or Monday. Of course that means more than half keep us dry through the holiday weekend. This chart shows each of those 51 members as one horizontal line on the upper half of the image. It’s 24 hour precipitation.

Anything with some color (not gray) means at least .10″. So details for next weekend are still to be resolved, but we know at least Saturday will be dry.

FIRE WEATHER

The cooldown and lack of thunderstorms the 2nd half of August has had a HUGE impact on fire weather. There has only been ONE big new fire in the state of Oregon in the past three weeks. That was the Fox Complex near Lakeview. No other new fire over 1,000 acres has ignited. Very good news. We still have 5 large fires (over 100 acres) burning in Oregon this evening, that’s down from around 10 a couple weeks ago. It’s 4 different complexes that started from lightning the first few days of August, plus the Jack Fire which began right around the 4th of July. That fire hasn’t seen much growth at all the last couple of weeks. But the other 4 keep burning steadily

The Bull Complex is an interesting one because it’s burning in a relatively small area between three of those mega-fires last September, maybe 5-8 miles north of Detroit.

That’s it for now…although I do have some “mixed emotions” news to share. Anne Campolongo has been a big part of our weather team for the past three years; the best weather team I’ve worked with. She’s one of the most professional people I know; smart meteorologist, friendly, great sense of humor, willing to learn, and really enjoys life. She came to us from Medford, just two years into a TV career after a meteorology degree. But now she moves on with 5 years experience in this business. Heading to the “big time” weather-wise! KCCI-TV in Des Moines, Iowa. That will be quite the severe-weather experience. Tornadoes, blizzards, damaging thunderstorms, etc… It’s also much closer to where she grew up in Ohio. So we’re sad she’s leaving, but happy she is headed to a good place. Goodbye Anne!


Is Summer Over? Not Really, But It Feels Like It!

August 22, 2021

9:30pm Sunday

What a tremendous change the past week! Take a look at high temperatures in Portland. 100s to 90s to 80s to 70s. Today we just barely made it to 70, which means we spent the whole day in the 60s. This weekend was the coolest we’ve seen in over two months.

I had a few days off last week, but working this weekend. I’ve had plenty of time to get up to speed and here’s what I’m seeing:

  1. We had our usual two month period of guaranteed warm/dry/sunny weather, but it was a bit early… June 15th to August 15th.
  2. The heat of summer is gone, and there’s no sign it’s coming back. Endless days of sunshine are done for this year. Sure, we should have plenty of warm/dry weather ahead, but expect marine air to flood inland at times too. Just like this weekend, we will have cloudy or mostly cloudy & cool days mixed in.
  3. We can still get up to 90 for about another month, but no model is projecting that for Portland through the rest of the month. We’re just 10 days away from September.
  4. I don’t see a soaking rain, or even widespread showers, for the next week

With 9 days left in “meteorological summer”, we’re still on track for the hottest summer on record. That’s both in Portland and Salem, but it’s going to be close with this recent cooldown. It may end up the 2nd hottest. Regardless, both cities DID experience the warmest 2-month period on record from mid-June to mid-August.

One surprise, and a mild forecast bust, was the heavier than expected showers today. Many areas picked up measurable rain, and .05-.10″ was not uncommon. Almost all of it was central/east metro

That makes August 22nd the 2nd day with measurable rain this month at PDX.

WHY A COOL END TO AUGUST?

For at least half the time, we’ll be under weak upper-level “troughing” or a dip in the jet stream through the end of the month. Right now a chilly system is passing by to the north in British Columbia; excellent news with all the fires up there. Here’s the Canadian model’s representation of the current setup. Cool showers up north plus lots of cool northwesterly flow coming down the B.C. coastline into Oregon/Washington

That moves east, we warm up a bit tomorrow, then quite a bit Tuesday/Wednesday. But Wednesday night another “ripple” is moving by, pushing lots of clouds inland. We’ll likely see some drizzle again Thursday morning, and some models even produce real showers Wednesday night and Thursday A.M.

By Saturday, a warm ridge is developing to our west (zig-zag line)… that’s sunnier, warmer, and back to “summer weather”. NEXT WEEKEND LOOKS SIGNIFICANTLY WARMER/SUNNIER THAN WHAT WE JUST EXPERIENCED

But just four days later, another cool trough is approaching. This is Wednesday, September 1st

What about rain? As of now, there’s no sign of a significant cool/wet spell. The ECMWF ensemble forecast for the next two weeks doesn’t show that either. Although there could be drips/showers here and there (possibly Thursday/Friday).

To summarize…

SUMMER ISN’T OVER, but if you want lots of hot weather, that’s not happening in the next 10 days.

FIRE WEATHER

This is EXCELLENT news! The last outbreak of lightning was back in the first few days of the month, and I don’t see any ahead. It appears we’ve only had one large (over 1,000 acre) fire develop in the past two weeks. That is the Fox Complex near Lakeview.

What’s ahead

  • Cooler plus higher humidity with occasional onshore pushes means less chance for huge fire starts, plus existing fires grow slowly
  • Westerly flow will continue send smoke east of the Cascades most of the time the next 10 days
  • I don’t see a setup where we get significant smoke west of the mountains over the next week and beyond
  • This weather pattern does not produce the dangerous easterly wind with its low humidity and high temps

The largest fires (or complexes) burning right now in Oregon

It’s good that we don’t have any sort of hot easterly wind event in sight…6 of those fires are burning on the west slopes of the Cascades!

I’ve said for years that what the weather does DURING fire season is far more important than the lead up in the spring. Remember we had our driest spring on record and most of Oregon is in severe drought. BUT, if we keep lightning away, humans don’t start fires, and we get occasional cooldowns/showers, we can make it through the rest of the season…fingers crossed

Chief Meteorologist Mark Nelsen


Hot Summer Temps Are Gone For At Least A Week

August 16, 2021

9pm Monday…

The heatwave ended today; a beautiful blue sky, temperatures in the 80s, and much lower relative humidity

That was after a sweaty six days of 90+ degree weather, peaking midweek with the 102 and 103

What’s Ahead?

  1. There’s no sign of a heat wave, or even 90 degree temperatures, in Portland during the next 7-9 days
  2. Other than a sprinkle/shower tonight & Tuesday morning, or a light weekend shower, the dry spell continues
  3. This next week will have that “the heat of summer is over” feel. Nights are getting longer and we’ll be cooler each morning
  4. Expect more cloud cover, especially mornings Friday through next weekend.
  5. Most likely we’ll turn warmer again during the last full week of the month (after the 24th)

Sunday was our 24th day at/above 90 in Portland. That’s the 3rd highest number of those hot days…after 2015 & 2018.

With two weeks to go in meteorological summer (June-August), many parts of the Pacific Northwest are on track for the hottest summer on record. That includes Portland, Salem, Eugene, Medford, Olympia, Pendleton, Burns, & Redmond. It’s interesting that North Bend isn’t even close. That’s because that location is dependent on warmer than normal ocean waters for a “hot summer”. And 1997 is the all-time high there due to the Super-Nino that year.

Of course we still have two weeks to go. This next week looks a bit cooler than average; starting with a mainly dry cold front passing overhead this evening. You’ve probably noticed the cool northwesterly breezes, clouds, and quickly dropping temps. This is associated with a cool upper-level system dropping down into Eastern Washington. Another one drops in over us or just to the east again around Friday. The result is more typical late summer weather; onshore flow plus cloud cover at times, then sunny periods. You can see the ECMWF forecast for the next week, showing a strong upper-level ridge (above normal heights in the higher atmosphere) in the Gulf of Alaska. That leads to lower than normal heights and upper-level troughing over Idaho. This is the pattern that gave us a dry and cool-ish spring at times.

But most models (including this one) show the ridging edging closer to us NEXT week. This is Sunday the 22nd through Sunday the 29th; a warmer pattern again, although not necessarily hot.

Both patterns (this week and next) are relatively dry; there’s no sign we have a late summer showery pattern setting up.

Enjoy the comfortable weather the rest of this week! Chief Meteorologist Mark Nelsen


Extreme Heat is Gone, but Hot Weekend Still Ahead

August 13, 2021

9:30pm Friday…

A quick post this evening. Here’s a summary:

  1. We are done with 100 degree temps, we’ll be in the mid 90s tomorrow, then lower 90s Sunday
  2. Humidity remains relatively high this weekend
  3. Smoke coverage will be similar tomorrow, if not a bit less, west of the Cascades
  4. Most of the smoke disappears Sunday afternoon; both at lower elevations and high overhead
  5. Heatwave #4 this summer will end up with 6 consecutive 90+ degree days

A thick layer of smoke kept us below 100 west of the Cascades today; we’ve been thinking all this week it might happen. Smoke modeling did pretty well!

This was our 22nd day at/above 90 degrees in Portland this summer.

But Salem just broke the all-time record. Today was the 35th day at/above 90 degrees. Those records go back into the late 1800s!

Strong high pressure remains nearby through Sunday, but increasing (cooler) onshore flow means temperatures drop a bit over the weekend.

HRRR smoke modeling has done relatively well the past two days, and it shows slightly cleaner air (at ground level) tomorrow morning

Then a 2nd push of marine air tomorrow evening really clears things out. By Sunday, just about all low-level smoke should be gone…we’ll see!

That’s it for tonight… Enjoy your weekend!

Chief Meteorologist Mark Nelsen