A Week of Warm Afternoons & Chilly Nights

7pm Sunday…

Weather forecasting is VERY simple this next week.  A strong upper-level ridge of high pressure has moved over the West Coast and should remain in this general position through NEXT weekend.  This is what it looks like today overhead:

 and next Saturday, not much change is there?

This is a very stable pattern, especially when I see the same thing on just about all the models and good agreement on the model ensembles themselves.

The east wind showed up, but far weaker than what models were showing Thursday night, the last night I was at work.  They were indicating 6-7 millibars easterly flow through the Gorge or at least from the Columbia Basin to Portland.  Instead it peaked at a paltry 4 mb. this morning.   Crown Point had a gust to 52 mph, weak sauce even for October

We DID get the downsloping wind today though, dropping dewpoints well down into the 20s for many areas west of the Cascades.  There is one good way you can tell the difference between a regular “Gorge gap wind” and a more unusual downslope wind.  The wind direction with a typical easterly wind event in the cool season is ESE or even SE at PDX.  A downsloping-type wind is E or NE at that location; something I noticed early in my career here.  To summarize the weather pattern the next week?  We’re living in “Central Oregon” right now weatherwise; warm sunny days and cold nights.

This general setup continues through next weekend.  The result will be light frost in spots away from the wind tonight.  The Olympia to Eugene pressure gradient (northerly) is still around 5 millibars this evening which leads me to believe there will be areas of northerly wind at times all night in the Willamette Valley.  That also makes me think frost will be patchy.  We’re going to see some spots (in the breeze) stay in the 40s tonight and calm areas drop to around 30.

How much longer will we remain dry?  Models seem to want to break the ridge down early next week (around Tuesday the 23rd), bringing in more typical late October rains at that time.  Check out the rain on most of the ECMWF ensembles suddenly showing up at that time

The top chart shows each of the 51 ensemble members as a horizontal line with accumulating rainfall.  Notice almost all of them produce 1″ or more total rainfall by the 29th.  The average is 2.30″ or so, seen on the bottom chart.  So this EPS shows a very wet pattern for NEXT week.  I noticed the GFS doesn’t seem to want the ridge to disappear through the next two weeks; showing just a bit of a breakdown next week but it doesn’t totally go away.  I’m pretty confident we can forget any chance of a cool & wet pattern through the end of the month, but we may have a mild & wet pattern ahead!

Short-term, offshore (easterly) flow continues through Wednesday, then turns weakly onshore Thursday.  That upper-level ridge rebounding late Friday through Sunday gives us another round of gusty east wind.  Temperatures warm a few degrees tomorrow through Wednesday.  Back off Thursday/Friday with onshore flow, then models are pushing us up to +18 to +19 850mb temps Saturday…that would put us into the upper 70s!

Enjoy the sunshine!

1st East Wind “Event” Of the Season This Weekend

9pm Thursday…

You’ve probably noticed; we have entered a remarkable period of mid-October sunshine!  Today was totally sunny except for some spots of brief low clouds and/or fog.  The next 6 days should be mainly cloud-free, or just plain sunny as you can see in our 7 Day Forecast (which you can always find here)

The reason is a strong upper-level ridge shifting from the eastern Pacific directly over the Pacific Northwest.  It’s going to stick around for quite a long time.  Here’s the forecast from GEFS (GFS ensemble system) for Monday.  Lines are upper-level heights, colors are the anomaly (red = above normal, blue = below).

Then next Wednesday from the EPS (ECMWF ensemble prediction system)

The ridge appears to be strongest at that time.  Looking farther ahead is stretching the limits of weather forecast models, but most interesting is that they all show a similar setup through Day 10…NEXT weekend from the EPS.  Not quite as extreme, but warmer and drier than normal.

So it appears that we are in a long (7-10 day) stretch of unusually dry and warm weather in the Pacific Northwest.

But there is a wrinkle to this forecast…not all of you will be able to enjoy the sunny & warm weather as much because of…the wind.

We’re quickly approaching the cool season (November-March) and that means “East Wind Season” too.  Fall and Spring feature the seasonal oscillation from westerly Gorge wind to easterly wind.  In this case surface high pressure drops down the back side of the upper-level high Saturday through the middle of next week.  Strong high pressure east of the Cascades will give us quite a strong pressure difference across the Cascades.  You can see it on the WRF-GFS surface map for Sunday morning.

That’s 7 millibars easterly gradient from the lower Columbia Basin (near The Dalles) to Portland both Sunday and Monday mornings.  That’s a very strong east wind for October.   Plus, from Saturday afternoon through early Monday it will also be a “downslope” wind.  The layer of easterly flow is deep enough to move right over the Cascades and down into the valleys.

What does that mean for us?

Much of the metro area will be very windy Saturday afternoon through early Monday.  Expect gusts 20-35 mph in the windier spots with gusts at the west end of the Gorge in the 40-55 mph range.  Probably a few scattered power outages as well…under sunny & blue skies.

Of course Crown Point will be a bit stronger…maybe gusts 60-65 mph for the first time this season.  Those highs in the upper 60s will feel quite a bit cooler out there in that wind!

You can see this on the WRF-GFS time/height cross-section over Portland.  Time goes from right to left.  Starting at 5am today (right side) and ending 5pm Sunday on the left.  You see a few 50 kt speeds around 2,500′ over Portland Saturday night and Sunday AM.  That’s impressive even for winter!

The pressure gradient will drop off a bit Tuesday & Wednesday confining wind to the Gorge.  At that point temperatures will likely peak here in Portland as the wind backs off.  We should reach mid-upper 70s on those days.

Enjoy the sunshine Friday and into the weekend, but be ready for things to blow around a bit too!

Chief Meteorologist Mark Nelsen

Winter 2018-19 Thoughts

6pm Monday…

I just posted a “page” up above (note the tabs) on this upcoming winter.  Check it out!

Wet Start This Week, But A Warm & Sunny End

7pm Sunday…

For those of you who wondered “Will the hot weather EVER end?”  Here you go…

Cool fall weather along with clouds and rain ALWAYS comes back in our climate…always.  Even in a slowly warming climate the clouds and showers will continue to come back.  Yes, some autumns are warmer than others, but hot weather doesn’t “go on until November” as one viewer worried in a summertime email I received during a hot spell.

Why so gloomy today (and much of yesterday?).  There is a large upper-level high blocking all storminess to our west

The big ridge of high pressure is just far enough west that very weak disturbances with clouds & light rain are moving down the backside of the ridge.   Basically “the back door is open” and won’t close until Tuesday PM.  At that point the ridge starts pushing closer and eventually ends up almost right on the coastline by the end of the week.  Here’s Saturday:

Then it appears to linger over us for a few more days.  Models are in excellent agreement on this scenario.  A few key points:

1. Gray & cool temps continues through Tuesday, although by Tuesday afternoon we should see a few sunbreaks
2. Rain picks up a bit tonight and Monday, but will be most noticeable east metro and near hills/mountains
3. Rain ends all areas by Tuesday evening with no rain expected again until at least Tuesday the 16th (at the earliest).  For agricultural folks: you have at least a 5-7 day window of dry and mainly sunny weather beginning Wednesday
4. Offshore flow later Wednesday through much of the following 5 days = bright blue skies with abundant sunshine and warming afternoon temperatures
5. Next weekend MAY be spectacular for outdoor activities

 

Notice the RPM rain forecast for the next 3 days (most of it is done by Tuesday PM) shows a very strong orographic rain event.  That means northwest/westerly flow runs into the north/south oriented mountain ranges, rises, and dumps a load of rain on the windward slopes.  On the lee side of the Coast Range there won’t be much more than sprinkles or a light shower the next two days (Washington & Yamhill counties).  But in the “upslope” areas on the east side of the Willamette Valley and into the west slopes of the Cascades you can expect widespread rainfall much of the next 48 hours.

Note the ECMWF ensemble forecast for 24 hour precipitation shows a huge gap (almost no ensemble members expect rain) from Tuesday night through about the 16th as the ridge moves overhead.

although many show a wet pattern resuming soon after that time.  The GEFS is similar with most model members showing a return of rain the middle/latter part of NEXT week as the ridge pushes farther east.

So enjoy the gray, and then get ready to enjoy warmer sunshine later this week; quite a change ahead.

Chief Meteorologist Mark Nelsen

 

 

Cool Weather & Early October Soaker On The Way

9pm Wednesday…

This morning was chilly!  Temperatures dropped well down into the 30s in many parts of the metro area; stopping at 44 right in the city at PDX.

This afternoon was “comfortably cool” I suppose with highs just a few notches below normal.  Tomorrow looks dry or mainly dry (just a slight risk of an afternoon sprinkle) as a cool upper-level trough passes overhead.

Friday gives us our first rainy/overcast/chilly day of the season.  A surface low pressure system tracks right into northern Oregon during the afternoon, pushing a large shield of rain/clouds ahead of it.  Here’s the early afternoon view from our RPM model:

And total rain forecast…looks like up to 1/2″ or so in the valleys of western Oregon and southwest Washington.  The best news is that this system will finally bring some light rain to those of you east of the Cascades.  Not a lot, but enough to settle the dust in central and north-central Oregon.  These areas haven’t seen any significant rain since spring.

Looking ahead, the weekend should be pleasant, but a bit on the cool side with highs remaining in the 60s.  There is no sign of a stormy/rainy season start as a large upper-level high remains over the eastern Pacific the next 7-10 days.  Occasional weak systems will slide down the back side of the ridge (along the west coast of Canada and PACNW) and give us showers at times.  That keeps temperatures near/below average through at least the middle of next week.  I noticed the ECMWF ensembles warm us up around Day 10 as the ridge moves closer to us.

We’ll see how that works out.  Big picture = a mellow weather pattern over the next week.

PIC BY JULIE FONG

By the way, a bunch of you sent in pics of the “ice halo” around the sun this afternoon.  That’s caused when the ice crystals in the high clouds “refract” or bend the light at a 22 degree angle.  You can read more about it here:

http://www.atoptics.co.uk/halo/circular.htm

Chief Meteorologist Mark Nelsen

October Begins Cool, & Water Year Ends

6:30pm Sunday…

It’s been a real quiet weather weekend with just a few sprinkles/showers yesterday and today. Officially we’ve had all of…wait for it…  .01″ in Portland.  That’s weekend total.  I know a few of you had more, but overall boring for weather geeks like me.

Tonight (the end of September) wraps up the “Water Year”.  If you’re new to the Pacific Northwest there’s a very good chance you’ve never heard such a phrase.  Here’s the deal…our rainy season is late October through March; during the cool season.  As you know, we have a very dry warm season here compared to areas east of the Rockies.  That’s May through September.  All that winter rain (in the ground) and snowmelt (coming down rivers) is used to sustain our lives/properties/crops through the dry season.  So it’s important to know how wet our rainy season is each year.  But each rainy season crosses from the end of one calendar year into the first part of the next calendar year.  So for the purposes of ranking our wet seasons, we use a “water year”.  That year begins on October 1st and ends September 30th.  Make sense?

How did we do this year?  We ended up drier than average by 6″or so.  Here’s a nifty little chart from the folks over at Portland NWS.  Winter rainfall was just about normal until we hit February.  But that month and March were drier.  Then a very wet first half of April brought us back to close to average again.  And you know the rest of the story…we’ve pretty much flat-lined since that time.

Comparing this water year to recent years shows we had two very wet “wet seasons” and now we’ve experienced a dry one.  You can see the big year to year variability.

The water year gauge “resets” at midnight and we begin a brand new year.

Here’s what I see for this first week of October:

1. Next few days feature a splitty flow with a southern system moving into California giving them a much needed rain.  We get a weak system dragging through here tomorrow night and Tuesday morning; sprinkles/showers at most during that time
2. A large upper-level ridge wants to develop out in the Gulf of Alaska (just to our west) later this week and through early next week.  This means a real lack of storminess in the eastern Pacific but also quite chilly air (for early October) just to our east.  Notice all 3 big models (GEM/ECMWF/GFS) show the same pattern for NEXT Monday, the 8th…one week from tomorrow

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A slight move westward and we’re into an unusually chilly (early frost?) pattern all across the Pacific Northwest.  A slight move east or a weaker ridge (ECMWF) would mean cloudier, but mild and occasionally wet weather.   We’ll see how it works out and how much rain we get next weekend.  ECMWF was somewhat wet so I went with that model.

3. No sign of a stormy October weather pattern.  With a large ridge out there we’re sure not going to see an extra-early start to the Pacific storm season here on the West Coast.

4.  Cool temps, or at least cooler than average.  We’re done with 80 degree temps and at this rate there’s no reason we couldn’t be done with 75 too.  Check out those ECMWF ensemble forecast highs the next two weeks…pretty cool this weekend and early next week

So the next week will be cooler than average with more showers toward the weekend but not a “start of the wet season”.

Chief Meteorologist Mark Nelsen

Beautiful Weather; Last of the 80s?

6pm Wednesday

Today has been another fantastic fall day.  A chilly start with lows in the 40s and lower 50s, then all areas west of the Cascades in Oregon made it well into the 80s.  Check out those lower 70s on the coastline as well

I saw someone mention somewhere on social media that this is summer weatherwise.  Most definitely not.  The long nights and low sun angle give a totally different feel.  It gets warm between about 2 & 6pm in this pattern, but cool during the lengthening nights, mornings, and evenings.  Even here in the city it was still only 69 at noon.

Strong high pressure centered to our west over the Eastern Pacific remains in place through Friday and that guarantees us two more days above 80 degrees.  Then lowering upper-level heights plus a strong onshore push drop us 10-15 degrees Saturday for a more typical late September day.

So is this the last of the 80 degree temps?  It could be.  Check out the past few years…specifically the last date we hit 80 each of those years.

The average for Portland (in any year) is September 29th.  Last year we hit our last 80 on this date (the 26th).  After this Friday there’s no sign we’ll hit 80 in the following week, although the ECMWF ensemble forecast highs for Portland do hint at warming again late next week.

That said, models have not been doing real well handling a split-flow setup Sunday and beyond so I have low confidence beginning that day.  I’m not a fan of putting question marks on the 7 Day forecast (and we don’t do that here) but early next week would be the time to use them!

Here’s a plot I use regularly…the ECMWF 850mb temperature ensemble plot.  This is temperature in celsius up around 5,000′.  Each thin line represents one of the 51 members of the “ensemble forecast system”.  Basically each line is one run of the model and it’s done 51 times every 12 hours.  The blue line is the actual “operational” model run and has a bit higher resolution.  Red line is the average of all the ensemble members.  You can probably guess what the yellow/green line is…climatology.  Temperatures up around 5,000′ drop quickly the first two weeks of October.  You can glean a bit of info from this chart; I noticed two items today.

1. Good agreement among ensembles (all the lines close together) through Sunday…the 30th, then they are all over the place.
2. Temperatures are well above average through Saturday AM, then plunge to below/near average after that time.  Looks like we’ll be all done with the 80s down here at sea level after Friday.
3. BUT, look at that range the middle of next week!  That could give us a high of 85 or as cool as 58, best to just keep the 68-70 for now until the solutions come together.

By the way, today is the 71st day we’ve hit 80 this year in Portland

As we all know, the past 5 warm seasons have been VERY warm; quite a contrast with those much cooler years 2010-2012.

Chief Meteorologist Mark Nelsen