A Week of Warm Afternoons & Chilly Nights

October 14, 2018

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:

Jet Stream Forecast 2017 and next Saturday, not much change is there?

Jet Stream Forecast 2017_a

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

Wind Peak Gust Gorge Crown Point

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.

Forecast Tonight Metro FOX12PLUS

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

KPDX_2018101412_eps_precip_360

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

October 11, 2018

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)

7 Day Forecast Graphic 2017

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).

gefs_mon_am

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

eps_wed_am

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.

eps_sun_21st_10days

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.

wrf_sundayam

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!

kpdx.th

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

October 8, 2018

6pm Monday…

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

Mark ElNino PacificNorthwest Effects2


Wet Start This Week, But A Warm & Sunny End

October 7, 2018

7pm Sunday…

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

Live Cam Portland

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

Jet Stream Forecast 2017

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:

Jet Stream Forecast 2017b

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.

RPM Precipitation Accumulation

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.

KPDX_2018100712_eps24_precip_360 (1)

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.

KPDX_2018100712_gefs_qpf_384

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

October 3, 2018

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.

PDX Observed Low Today

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:

RPM Clouds Rain

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.

RPM Precipitation Accumulation

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.

KPDX_2018100312_eps_min_max_15

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

JULIE FONG PIC

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