Three Warm Days Ahead, Then A Saturday Soaking

May 26, 2020

10pm Tuesday…

A shorter blog post tonight since we have a very straightforward weather setup the next 5 days.

Skies are mainly clear this evening and should remain that way through Friday. Maybe not totally blue sky; we’ll likely see thin high clouds at times Thursday and Friday.

The atmosphere overhead warms tomorrow through Friday as strong upper-level high pressure builds over the western USA. Stockton and Sacramento (California) were 105 & 103 today; both records for the date.

The combination of a much warmer atmosphere overhead, then a switch to (very weak) offshore flow Thursday, means we get close to 90 both Thursday and Friday. That’s very warm, but definitely not hot. Notice we won’t be near record levels except Friday

That 100 degree record for May 28th is the first day PDX has ever hit 100 and also the only 100 degree record in May.

Saturday is beginning to look interesting. A cool upper-level trough suddenly scoots north along the West Coast Friday night and Saturday. There is a LOT of subtropical moisture with this one, check out the precipitable water image for Saturday. Anything over 1.0″ is juicy for us. Up around 1.5″ is really wet. This isn’t precipitation, but a good indicator of total column moisture through the atmosphere.

How much rain could we be looking at Saturday? It seems clear that SOMEWHERE in western Oregon will get nailed with an inch or more. Each model is a bit different with the rain bullseye. Plus it’s still four days away. Check out the GFS, GEM, & ECMWF

Will we get thunderstorms with the rain Saturday? Possibly…TBD. It depends on how things line up. The general pattern is correct, but models don’t seem too excited about widespread thunder west of the Cascades Saturday. We’ll see.

Sunday through Tuesday look quieter and mainly dry. Expect typical early June weather as we head into early next week.

Enjoy the warm sunshine these next three days, and be prepared for some downpours at some point Saturday. I’ll be back at work Sunday. A few extra days off this summer.

Chief Meteorologist Mark Nelsen

Another Taste of Summer This Week

May 25, 2020

It’s been a very “normal” Memorial Day Weekend. Cool and cloudy Saturday, then warm and sunny Sunday. Of course a weak weather system lingering overhead the first half of today left us damp through noon or so. We expected that. We eventually warmed into the upper 60s in the Willamette Valley.

Memorial Day High Temps

Portland ended up with .07″ rainfall, about what models were showing last night at this time. A mix of sun, clouds, & showers are perfectly normal for this “beginning of summer” weekend. Take a look at Memorial Day Weekend weather the past 10 years (click for a better view)

PDX Stats for each Memorial Day Weekend

What’s Ahead?

We are in flat “westerly flow” right now. That means a weak late May jet stream is overhead. That’s why a wet weather system is lingering so close this evening.

But that warm upper-level high pressure to our south pushes north and east the rest of this week. By Thursday/Friday it’s centered right over Nevada

A heat wave is coming for California this week. Excessive heat warnings are up for the Central Valley. Highs reach upper 90s to upper 100s tomorrow through Thursday!

Scorching heat next few days in California

How warm for us this week? Tomorrow we’ll be back into the 70s; lots of clouds leftover from today will keep temps under control. But then weak offshore flow Wednesday/Thursday plus 100% sunshine warms us dramatically. 850mb temps reach +14-16 Wednesday, then +17-19 Thursday-Friday. With good offshore flow, there’s no reason we couldn’t hit 90 in Portland both Thursday and Friday. But I see “flat” upper-level ridging, plus most models are not showing a sharp thermal trough. So I’ll go a bit more conservative with the highs. 85-90 is a good forecast for those days. Anything over 87 would be the warmest day so far this spring in Portland. Enjoy another taste of summer, but without the record heat. By the way, record highs at PDX for Wednesday-Friday are 95-100-90.

I’ll be watching Saturday closely since a “cutoff” upper-level low is forecast to swing north along the West Coast. Sometimes this can give us a good soaking and/or thunderstorms as it passes by. That southeasterly upper-level flow just ahead of the low (shown) is great for steering some thunderstorms west of the Cascades.

Models are in very good agreement that we move into a wetter/cooler pattern again after Saturday. Check out the ECMWF ensemble rain forecast. Each line on this chart (upper part) represents one of the 51 ensemble members from this morning’s run. Great agreement that we’re dry through at least Saturday morning. Then every member shows showers later Saturday through sometime Sunday. Get your deck staining done this week and wrapped up Friday. Or early Saturday would be a good time to put out some warm weather veggie transplants; they will get watered over the weekend.

That’s it for now…enjoy the warm weather this week!

Chief Meteorologist Mark Nelsen

May Turns Wet; Metro Downpours Tonight

May 18, 2020

9pm Monday…

Suddenly it feels like a normal May weather pattern is back, like an old friend.  All of us have seen at least a bit of rain the past few days, but some of us have seen tremendous gully-washers.  This is overdue, not just because we’ve been dry the past 9 months, but we’ve had quite a run of dry May weather.  We’ve seen 5 consecutive years with drier than average May rainfallRain May Recently

We’ve seen measurable rain in Portland each of the past 8 days.   Yesterday afternoon/evening thunderstorms moved over the Salem area and Colton/Estacada/Sandy.  There were some 1″ totals around Colton at that time.  Then a weak “deformation zone” sat over the area this morning and midday.  That dumped up to 1/2″ rain in some spots around the Portland metro area.  Finally, a batch of showers moved south through Clark county and central/eastern Multnomah county this evening.  It appears that the area from Troutdale to Happy Valley was nailed with the heaviest rain totals.    This was the radar view around 7:45pm

KPTV 2017 Default Earth

Daily totals at 9pm look like this; these are from official airport locations

Rain Metro Today Databound

But these small/intense showers have dumped even more in a few spots.

Rain Totals Metro Area

The good news is that these showers are making up for what has been a very dry spring.  The bad news is that we have a lot of cloudy/wet weather ahead.  The cool upper-level trough over the Pacific Northwest right now heads east tomorrow


But by Thursday/Friday another cool upper-level low is right over the region once again


In-between we get strong onshore flow both tomorrow and Wednesday.  This means almost solid cloud cover west of the Cascades, although not many showers.  Once we add in the showers Thursday and Friday from the new low, rain totals look something like this for the next four days

7Day Interactive 4

This will be a strongly “orographic” rain setup the rest of the week.  Areas just downwind from the Coast and Cascade ranges will be relatively dry (Hillsboro, McMinnville, The Dalles, Maupin).  But in the constant westerly flow the “upslope” areas will be wet…wet…wet.  If you live in the Cascade foothills or western Gorge, I hardly see any dry weather through Friday.  Yes, that sunshine in March, April and early May was nice, but it’s make up time now.

What about Memorial Day Weekend?  A weak ridge will be over us Saturday/Sunday then get “squished down” a bit toward Monday/Tuesday.  That means Saturday looks dry, but showers possible Sunday/Monday.  But that’s way out there in time.  We’ll nail down that weekend forecast as we get closer.

Enjoy the showers!


Normal May Weather Sticks Around For Another Week

May 13, 2020

6pm Wednesday…

We’ve seen a few showers the past few days, quite a change from the 80s last weekend.  We ended up with three new temperature records from that warm spell.  A record high of 87 Saturday, then two record warm low temps (59 Saturday/Sunday mornings)

Mark Hot Heatwave So Far

Since Monday we’ve been under the influence of a cool upper-level low (a dip in the jet stream).  It has been sending waves of showers/clouds up over the Pacific Northwest.  Not so much rain yet, but I think that action will pick up tonight and Thursday.   Portland has picked up all of .20″ so far this week but we’ll at least double that in the next 24 hours.

It has been a very dry spring.  In Portland it’s the 7th driest on record and our driest since 2013.  Some stats for spring so far…


But it’s only temporary, our springs in general have been turning a bit wetter over the long term.  Remember the soakings around 2008-2012?  You can see the gradual rise in Salem’s longer weather history (compared to PDX)…


What’s ahead?  A brief upper-level ridge moves overhead Friday, but then another cool trough drops in late Saturday/Sunday.  The ECMWF shows the cool low over us Monday.  Also notice a real warm ridge over the southern Rockies and Plains states.


A third upper-level low will be dropping in a little over a week from now.  This is Friday the 22nd.  Just heading into Memorial Day Weekend.


So it’s clear that we’ll see normal to slightly below normal afternoon high temps the next 7-9 days, although that will be countered a bit by cloudy/mild nights.  We should make up at least some of that rain deficit, but probably not much.  The 10 day anomaly through Saturday the 23rd; a bit wetter than average, but not unsually wet.


To summarize

  • Lots of clouds/showers the next 7-10 days.
  • It won’t be continuously wet though, in fact parts of next Tuesday/Wednesday may be dry
  • There’s no sign of a significant warm/dry spell until at least Memorial Day Weekend

Chief Meteorologist Mark Nelsen

Four Days of “Summer” Begin Thursday

May 6, 2020

10pm Wednesday…

A very weak cold front passed through the region early today, dropping all of .05″ rain at PDX.  That’s been the story so far this spring, weak systems and warmer than normal weather.  I think it’s fascinating that the last three Aprils in Salem have been warmer than ANY April from the early 1950s to late 1980s!  That’s what we call “cherry-picked” data because it’s such a specific statement.  There WERE lots of warm Aprils in the 1920s through 1940s.  We not only have a gradually warming climate, but there are cyclical patterns occurring too.

Just a quick post this evening to let you know we still have quite a warm/hot spell (for early-mid May) on the way.  As mentioned in the previous post, a strong upper-level ridge will be over us now through Sunday.  The atmosphere overhead warms quickly tomorrow and stays very warm through Sunday.

Mark Jet Stream

By the way, record cold will be descending on the northeast USA.  Some rare May snow is on the way for parts of New England the next few days.

Wind flow over our are switches to “offshore” or easterly tonight.  From tomorrow through at least Saturday evening we’ll be in that offshore flow.  Check out the cross-section of the atmosphere over Portland.  Time goes from this morning (right side), to Saturday 5pm on the far left side.  700 refers to about 10,000′ overhead (top of Mt. Hood), and 850 level is around the Cascade Pass elevation.  You see easterly flow begins around sunrise tomorrow and goes strong all the way through Saturday afternoon.  It extends up to around 4,000′ or so.  Expect a gusty easterly wind for much of the metro area Friday and Saturday.


How warm/hot will we get?  Over the past two days we’ve bumped up our high temp forecast a few degrees.  That’s due to models in excellent agreement showing temps at pass elevation around +16 to +18 C.  Past situations (including exactly one year ago) have seen 85-90 degrees in this setup.  So this is what we expect for the next three days; and there’s no reason we can’t hit 90 on Saturday.  All of the record highs on this graphic occurred in May 1987.

Mark Hot Heatwave So Far

I remember that hot spell since it was my senior year in high school.  Most likely spent a night or two cruising the strip in Centralia (WA)…old memories.

Make sure you are watering all potted plants and also pay close attention to any flower/veggie beds that look dry.  Easterly wind always dries out the ground quickly in our climate, especially so this year since spring has been drier than normal.

I’ll be off Thursday-Saturday; three day weekends this summer like many of you are seeing due to current economic issues.  No complaints here considering the weather this weekend.  Time to get the pool cleaned up, and stain a deck!

Chief Meteorologist Mark Nelsen

Our First “Heat Wave” Late This Week

May 4, 2020

9pm Monday…

May has arrived after the 4th driest April on record in Portland.  Less than 1″ of rain through the entire month!  That’s mid-summer dry.  Some areas west of the Cascades had a bit more…around 1.00 to 1.50″.  Still a dry month.  Warmer than average as well.

What’s ahead?

May in Portland Stats

May is typically the month where we turn the corner, leaving behind the really chilly spring weather.  We also tend to see some “very warm” weather at some point during the month.  In fact each of the past 8 years we’ve hit at least 85 at some point during the month.

May Warmest Temp

Most interesting is that the 89 last year occurred on May 10th.  That would be this coming weekend.  It appears we’ll be very close to that number again this Saturday.

We have our first warm season “heat wave” pattern setting up Thursday through Sunday.  The weather setup for these events is always similar.  Strong upper-level high pressure builds along the West Coast.  Then the sinking/drying of the airmass leads to surface high pressure east of the Cascades.  At the same time easterly wind around 5,000′ develops across the region.  That produces a “lee side trough” in western Oregon & SW Washington.  We also call that a “thermal trough”; an area of low pressure that develops on the “back side” of the Cascades due to the easterly flow.  That leads to a surface easterly wind as well since pressures are lower west of the Cascades.  This all adds up to the warmest possible weather for us anytime between April and September.  In the case of late this week, the atmosphere overhead won’t be crazy warm, so no 90s.   But we’ll be close.

You can see the progression of events on the Canadian model.  Strong surface high pressure building just north of us Wednesday afternoon.


Quick clearing that afternoon after some morning showers…ignore the colors.  Then by Thursday afternoon the “thermal trough” is getting established west of the Cascades, although it’s more of an northeast wind instead of straight easterly at the surface.


Friday is the big warm up, a very sharp trough is sitting right along the coastline.  Strong easterly wind through the Gorge and down the west slopes of the Cascade/Coast ranges


This is the one day the beaches may hit the low-mid 80s, especially north of Lincoln City to the Long Beach peninsula.

7 Day North Coast

The thermal trough is still west of the Cascades by late Saturday afternoon, but easterly wind goes calm.  This is typically the warmest day of the episode in the metro area; early east wind going calm or very light westerly late in the day.


By this time flow is back to onshore along the coast and maybe into the southern Willamette Valley too.  Could be a few degrees cooler from Salem south

How warm could we get Friday and Saturday?   It is possible we make it to 90 degrees. otherwise it’ll be close.

Models are in very good agreement laying down +15 to +17 (celsius) 850mb temperature both afternoons over Salem.  Based on past cases in early-mid May with offshore flow and 100% sunshine, PDX should see a high temp between 86 and 91!  Last year a +16 produced that 89 degree day on the 10th.  So our temperature forecast of 84 & 86 those two days might actually be a bit low.

Data Driven Forecast Highs Next 7 Day Meteogram

Regardless, we have several days of summer weather coming up Thursday through Mother’s Day.  Get your BBQs and kiddie pools ready…

Since it’s been so dry you should be watering everything starting this week, including your lawns.  Dry easterly wind really dries out potted plants quickly.  That’s too bad since it’ll be the third consecutive year we’ve seen very dry weather start early in the season.

Chief Meteorologist Mark Nelsen