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  • Updated

Friday, July 30th, 3:50 P.M. 

Happy Friday!

Clouds and a smoky haze kept today a bit cooler than expected, but it was still very warm with highs making it into the mid 90s around the metro area. We are seeing some showers on the radar, but most of the rain is very light and evaporating before it hits the ground. A chance of thunderstorms or light showers will linger tonight, especially over the Cascades.

Saturday brings more high clouds and a smoky haze above with highs in the low 90s. Expect that smoke to stick around on Sunday, but it should have little to no impact on our air quality.

After a couple more 90 degree days on Monday and Tuesday, things cool off midweek. Thursday and Friday bring our first decent chance of showers in over a month and a half!

  • Posted

It's a brand new year; we're 4 days into January 2021. What has changed over the past week? Not much; it's still mild and wet. We ended up with near average December rainfall in Portland. For the region as a whole it's been a very wet start this month. Astoria around 5" in just four days!

And 1.50-3.00" in the metro area

Not enough for flooding, but the ground is saturated. Precipitation the past month looks like a classic La Nina winter setup; a wetter than average northwestern USA, but very dry Southwest

Snowpack is running a bit below average over and west of the Cascades.

That's not due to lack of precipitation, but "warm storms". Or at least warmer than average. An example would be this past weekend. Just a few inches fell at Government Camp and snow depth hasn't changed. But 2 feet of snow fell up at Timberline Lodge (6,000') which stayed above the snow level most of the weekend. This is more of a typical wintertime El Nino setup...plenty of precipitation but mild storms. The last time I remember such a mild La Nina year was 2000-2001. At least in 2017-18 we had cold arctic air move south into the USA and give us a cold/icy/snowy Christmas. You see that trend continuing this first week of January. See forecast snow levels, based on 850mb temps off the ECMWF model

Some snow is again falling down to the passes right now, but a warmer system arrives Tuesday night and Wednesday morning. We do get a nice cold system Friday; should be a good snow producer for lower elevations in the mountains. You see another snow level spike the middle of the upcoming weekend. Although for now most of the precipitation with that system is forecast to fall in the cooler airmass with/behind the cold front.

What's ahead? More of the same for at least the next 10-15 days. Notice the ECMWF ensemble forecast high temps keep our highs near/above average. Ignore the last day, it stops in the early morning (when it's colder)

Almost constant westerly flow off the Pacific ocean is the culprit, in fact upper-level heights RISE a bit next week leading to even warmer temps! A break from the rain? No more than a day here and there; hardly any gaps on those same 15 day ensembles

You probably already know what that means for a lowland snow chance...essentially near zero through the first half of January, possibly all the way to around the 20th. It's somewhat startling to see not one ensemble member giving Portland significant (or any) snow in the middle of a La Nina winter.

The ECMWF ensemble 850mb temperature forecast shows almost no members below -6/-7, what we need to see to at least get snow down into the West Hills.

As for rain, intensity will probably back off in the next 10 days as upper-level heights rise. Notice a 3-4" forecast for Salem, that's just typical wet, nothing too heavy.

To wrap it up, the message remains the same as we head into the 2nd half of winter...mild and wet through the foreseeable future.

  • Posted

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...

MarkSpringExtraRainy

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)...

Capture

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.

ecmwf_wed

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.

ecmwf_friday22nd

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.

ecmwf-ensemble-avg-west-qpf_anom_10day-0235200

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
  • IF YOU NEED A DRY DAY, AIM FOR THIS FRIDAY OR THE MIDDLE OF NEXT WEEK
  • There's no sign of a significant warm/dry spell until at least Memorial Day Weekend

Chief Meteorologist Mark Nelsen

  • Posted

7pm Thursday…

It was dry today!  No rain in Portland today, what a nice break after so many downpours the past week.   Don’t get used to the dry weather, it’ll be wet again after midnight, plus Sunday should be a soaker too.  Maybe more important, all our models are showing even cooler conditions to wrap up the last 10 days of September.

Summer “ended” on September 6th this year in our area; that was the end of reliably  warm & dry weather.  There’s no sign of anything above 75 in the next week either and our very wet September will continue…

The updated September numbers so far for Portland.

Rain PDX Last 10 Days

A rain total above 3″ in September has only occurred a few times the past 30 years.  In 2013, 2010, & 1996.

Take a look at some other spots around the region, some hefty totals in the Coast and Cascade Ranges

Rain Totals Metro Area

The entire region has been wet too.  The precipitation anomaly for the past 10 days

cpc_gauge-oregon-10day_percent_anom-5200000

What’s ahead?

Real quiet tonight through Saturday, but a strong onshore flow and a dying weather system gives us light showers tonight through the morning commute Friday.  Saturday still looks great, at least compared to what we’ve seen lately.  Partly cloudy with temps making it into the lower 70s; at least a little more reasonable for late September.

Sunday = a soaker as an upper-level trough moves overhead accompanied by a cold front.  The entire first part of the day should be wet, then it’s on to showers the 2nd half.   Monday should be reasonable as showers end, but cool with 850mb temps only around +5.  Even with some sunshine the best we’ll do is mid-upper 60s.

Weather geeks will recognize the weather pattern the rest of next week; a classic arctic blast setup for wintertime Wednesday through Saturday.   Look at the ECMWF ensemble 500 millibar height chart for next Tuesday.  A strong ridge attempting to build over and just west of the West Coast.  Heights go up to around 580 or so which is typically warm fall weather.  Yet there is plenty of fast westerly flow overhead which keeps us from getting very warm with lots of cloud cover and maybe even showers making it as far south as northern Oregon.

euro_tues_24

But see what happens by Thursday a week from now?  The ridge is retrograding (moving farther to the west) and building over Alaska.  That forces a cold airmass to move south through Western Canada.  You can see a cold upper-level trough dropping south around Juneau.  At this point it’s showery over us (although not stormy) and snow levels are heading down toward the Cascade Passes for the first time this fall season.

euro_thurs_26

Then two days later…Saturday the 28th.  This is the pattern we had in February with cold (cool in September) Canadian air pouring south into the western USA.  A strong ridge is…wait for it…parked right over Alaska and the eastern Pacific.   Hmmm, just like February and parts of this past summer.  Interesting.  This pattern is not very wet and could give us partly cloudy skies with daytime highs in 60s and lows in the 40s.

euro_sat_28

I’ve only shown you the ECMWF ensemble maps, but the Canadian and GFS are very similar.  September will likely end cool.  The previous run of the ECMWF showed this similar “dipole” of a chilly western USA and warm east continuing into at least the first few days of October (through the next two weeks).  Surface temp anomaly from September 29th through October 6th…

sfcta_week2_bg_NA

The effect is clear; the 15 day ensemble low/high temps for Portland are almost all well below average for late September and early October

gfs-KPDX-gefs_downscaled-8916000

Summary

  • We are done with “summer weather” and even any significant warm & dry spells.  At least through the end of this month.  We can have spells of warm & dry weather in October, but that comes with nights in the 40s and highs in 70s; definitely not “summer-like”.
  • It won’t be quite as wet the next 7-10 days, but we could easily see another inch of rain or more in the next week
  • A first frost is likely many areas east of the Cascades within the next 10 days, and possibly a few of the coldest areas in Western Oregon and Southwest Washington.
  • Timberline Lodge at 6,000′ will likely see its first snow of the season about a week from now.  Snow may get down close to the Cascade Passes (briefly) too.

Chief Meteorologist Mark Nelsen