Wet New Year’s Eve, Plus Big Weather Change POSSIBLE For Early 2020

December 29, 2019

7pm Sunday…

It’s been a mainly dry weekend across the metro area, in fact officially we didn’t have measurable rain in Portland

Rain Metro Today Databound

We won’t see any rain tomorrow, and then maybe .25″ to .50″ Tuesday afternoon/evening before the rain “clock resets” for 2020 at midnight Tuesday.  This means 2019 will likely go down as the 7th driest on record in Portland.  Those records at PDX go back just under 80 years.  This is our 2nd consecutive dry year after a few wet ones.  By the way, there is no significant long-term shift in our precipitation; go back 100 years and we picked up about the same as now.  Temperature of course is a different story

Rain Year PDX

Speaking of 2020, how is it looking for your party plans weatherwise?  The good news is there won’t be snow or ice ANYWHERE over or west of the Cascades.  A very warm airmass surges in with southerly breezes Tuesday afternoon.  Sticking snow will be well above the timberline on Mt. Hood.  Here in the lowlands a strong westerly flow overhead means we’ll be somewhat “rain-shadowed” by the Coast Range.  It’ll be rainy at times Tuesday evening/night, but nothing heavy.  South wind may gust 30 mph or higher too.

New Years Eve Fcst

Up in the Cascades it’ll be a different story.  All models produce a LOT of rain from 8pm-4am New Year’s Day.  I highly recommend skiing during the daytime Tuesday when rain will be light.  It should be a downpour during the overnight hours, especially leading up to midnight.  Take a look at 24 hour rainfall from the WRF-GFS model, ending at 4am Wednesday

or_pcp_24hours_5amwed

You can see those black areas approaching 3″ rain in the Cascades.  Yet some spots on the valley may see only one tenth that much (Hillsboro).  That’s a clear signal of strong “orographic” lifting.  A strong flow of air perpendicular to mountain ranges (westerly in this case) forces moist air to rise, releasing LOTS of rain!

So we’re wrapping up a drier/warmer than average December.  That’s after a drier/average (rain/temps) November.  The main feature of this cold season so far is a persistent split in the jet stream near the West Coast.  This is happening while I write.  Parts of the San Francisco Bay area and Monterey have been soaked today.

These last two “storm seasons” have been the most boring I can remember (for a weather geek) for this reason.  Either upper-level ridging weakening storms over/west of us or a split jet stream sending energy south.  Of course last year the action suddenly picked up in early February with cold/stormy/snowy weather.  At this point, 2019-2020 storm season looks just like last year…so far.  I think we’ve seen ONE marginal high wind warning on the coastline in two months!  No storms in the Willamette Valley, no freezing rain, snow, or stretches of days with heavy rain/wind.  Cascade snow pack as of late December is tracking similar to those rough years 2014, 2013, & 2004.   About 3/4 of the typical snow pack we’d see on the ground around Mt. Hood is missing this year.

or_swepctnormal_update

THERE MAY BE A CHANGE AHEAD…BUT I’M NOT SOLD ON IT YET

For a quick summary, head down to the next headline…

Here’s the scoop, note the 500 millibar map for tomorrow morning.  Ridging building in over us while that disturbance soaks parts of California.

ecm_mon30

New Year’s Day:  A cool trough is passing by as the flow turns westerly overhead.  Showers and lower snow levels mean some snow in the Cascades after the New Year’s Eve soaking.

ecm_wed1

All models are showing this as the beginning of a pattern change where a strong upper-level ridge develops out around 160W longitude; a preferred spot if you want cool/cold winter weather in the Pacific Northwest.  Take a look at the 10 day forecast from the GEM/ECMWF/GFS models.  Actually these are the ensembles from each of those models.  Big ridge south of Alaska and cold upper-level troughing over us.  Each model is a bit different, but the same idea and they all get to this pattern by days 10-15 out in time.  So theoretically we’re headed into a cold weather pattern beyond Friday and of course we can get low elevation snow out of this setup if things work out right.

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BUT, models keep pushing that change out in time.  For example, this morning’s run of the ECMWF has a temporary ridge popping up over us Friday.

ecm_fri3

Just two days ago it showed a very cold trough bringing snow down at least to 1,500′ for Friday

ecm_oldfri_3rd

And farther ahead, for the middle of next week, the features are shifted farther east on current model runs compared to what we were seeing 1-3 days ago.  A ridge closer to us means the lack of  normal stormy weather would continue into early January (rainy/windy storms).  It also means Cascade snow gets shunted to the east too.  Just two days ago models were showing many feet of snow in the Cascades this coming Friday-Sunday.  Now we’re down to a foot or so.

So my concern is, for some reason, models still may not be catching onto the correct future placement of these features.  They are giving up on this persistent pattern we’ve seen since October.  This happened about six weeks ago too.  Remember in mid-November it suddenly looked like a very wet and cool period was ahead and we’d be done with the weak weather systems?  Rain for six weeks on the models?  I know this is hardcore weather geek stuff so I’ll summarize

SUMMARY OF WHAT’S AHEAD

  • New Year’s Eve will be wet, but not a soaker in the lowlands
  • New Year’s Eve WILL be a soaker in the Cascades…all rain up there
  • A Pacific cold front should drop snow levels down to at least 2,000′ or a little lower next weekend.
  • We MIGHT see a change to colder weather for NEXT week (6th-12th), but at this moment there’s no sign of a lowland snow “event” in the next 9 days.  That’s through Tuesday the 7th.

And by the way, Monday looks like another very nice day for late December…just partly cloudy.

For the skiers/snowboarders, here’s the Government Camp 7 Day forecast.  Should be some good snow Wednesday and then again next weekend.  Hopefully this will be enough to get Skibowl, Hoodoo, and Willamette Pass opened for the last few days of Christmas Vacation.

7 Day Forecast GOVT CAMP

 

Chief Meteorologist Mark Nelsen


Slow Weather Pattern Returns For Christmas Week

December 22, 2019

9pm Sunday…

Here we are, Christmas is just three days away!  The atmospheric river and flooding was sure exciting (although mainly north of us).  But now it appears the dull weather pattern we’ve seen since early October has resumed and will be with us for the next week or longer.

A weak upper-level trough is passing overhead tonight and early tomorrow; that brings a few light showers.  In the mountains maybe 3-6″ new snow by midday Monday.

RPM Snow Accumulation Mt Hood Zoom In

That snow is much needed for Christmas Break skiing.  You can definitely go ski/snowboard right now, but coverage is thin at lower elevations.  Skibowl and Hoodoo have not opened yet.  These next two weeks are critical for ski areas since so many people want to hit the slopes while on vacation.

At the 5,400′ elevation, a SNOTEL site has 22″ snow on the ground.  That’s the lowest snowpack in the past five years (on this date).

Mark Mt Hood Snowpack December

It’s more typical to see 4-5′ snow on the ground at that elevation.  There is just about no snow below 3,000′ in the northern Oregon Cascades; you can see that area is running only 25% of normal.  Only SE Oregon is seeing a typical snowpack for the last week or so of December.

or_swepctnormal_update (1)

What’s ahead?  After tonight’s system leaves the area, a 2nd even weaker system drops down toward California on Tuesday.  That one stretches apart, weakening as it moves onshore.  It’s possible we get no rainfall from this one.  Or just a few afternoon/evening sprinkles as Christmas Eve begins.  The evening GFS models gives us less than .10″ rainfall between sunset Christmas Eve and midday Christmas Day.  Obviously a non-event.  With morning fog/clouds leading to late afternoon/evening showers, it’ll be a very chilly Christmas Eve.  One would think it could snow that day, but checking soundings it appears that won’t be possible after midday or so.  A bit too warm overhead plus that above 32 degree airmass continues through the night and into Christmas Day.  This is assuming precipitation makes it inland!  That may not happen.

gfs-deterministic-oregon-precip_24hr_inch-7296800

Beyond that I see some weak upper-level ridging Thursday-Saturday for mainly or all dry weather.   The ECMWF ensembles for 500mb height Saturday…

ecm_sat_28

There are hints of some sort of pattern change right around the New Year.  But that’s 10 days away and a bit suspect considering how this season has gone.  I do see the GFS ensembles going for a rainier pattern about that time.  The lower part of the chart shows the ensemble average rainfall heading uphill next week.  We’ll see…

gfs-ensemble-all-KPDX-indiv_qpf-7016000

So how about travel weather?  MUCH better this week than that terrible Thanksgiving week.  Remember I-5 closing south of Ashland and I-84 issues in Eastern Oregon?  None of that this time.

First, the Cascades.   Roads should be snow-covered by morning and stay that way most of the day.  But I only expect 3-5″ at most tonight.  Not exactly a snowstorm.

Mark Road Holidays 1

Then that snow works off the highways the rest of the week.  That weak system Christmas Eve might drop an inch…maybe.

How about the Gorge?  Should be just fine for travel this week unless a skiff of snow accumulates with that Tuesday night system.  Or it’ll just stay dry.  Regardless, little effect on travel.  Farther east, I don’t see any organized weather system bringing snowfall into the Blue Mountains of NE Oregon

Mark Road Holidays 2

I-5 will remain bare north to Seattle and likely south into California as well.  That weak system moving onshore Tuesday midday/afternoon COULD drop some wet snow on the higher Coast Range summits, but I doubt that will cause any significant travel issues there.  Those Coast Range highways should be clear the rest of the week/weekend.

Mark Road Holidays 3

There you go…no White Christmas (sticking snow) for the western lowlands of Oregon/Washington, but maybe a dusting in the Gorge.  Maybe…

Merry Christmas!  I’ll be back at work Thursday

Chief Meteorologist Mark Nelsen


Flooding Rains North & West of Portland Metro Area

December 20, 2019

10:30am Friday…

An “atmospheric river” is pounding extreme NW Oregon and SW Washington with enormous rain totals this morning.  Look at those I-5 cities to the north of Castle Rock to Olympia; closing in on 4-5″ of rain.  And 7-8″ rain so far in the Willapa Hills.  These are rain totals since about midnight YESTERDAY

rainsofar

Meanwhile models have done well showing a a sharp southern edge to the precipitation; it’s rainy in west and north metro, but dry south and east.

web_radarnwor (2)

The warm southerly wind has pushed Portland to 59 degrees so far this morning, tying a record set on this date in 2014.  I see ski resorts are wet and mild as expected; although luckily Mt. Hood isn’t getting any sort of soaking rain with the precipitation staying up north.  This continues through this evening before a changeover to snow tomorrow and Sunday on the mountain.

Other than a few spots of high water the next 24 hours in the metro area (intersections, low spots etc…) I don’t expect any significant weather issues here.  It’s all about the north coastline and up into SW Washington.  Actually Columbia County is getting plenty of rain as well.

I’ll be back at work Sunday

Chief Meteorologist Mark Nelsen


Flooding Rains For Some of Us Friday

December 19, 2019

1pm Thursday…

Plenty of rain is moving through the region this morning…radar image is lit up like a Christmas tree

web_metroradar (4)

For many days weather forecast models have been forecasting an “atmospheric river” to develop across the eastern Pacific, sending tropical moisture northward into the Pacific Northwest.  Models have been in excellent agreement showing this basic setup and that heaviest rain would occur from late today through early Saturday.  But an atmospheric river is a narrow corridor; like a hose in the atmosphere.  It also tends to move north/south throughout an event as weather disturbances ripple northward.  So forecasting exactly which part of the region gets nailed by heavy rain is tough. But finally this morning models are good agreement.  The heaviest rainfall the next 36 hours will be between Pacific City and Hoquiam along the coastline (centered around Astoria), and into Southwest Washington (Woodland/Kalama to Olympia).

The Highlights

  • Rain continues at times through this evening in the Portland metro area and most areas west of the Cascades
  • After sunset and through the night, a band of heavy rain develops from around Astoria to Chehalis.  That heavy rain may extend as far south as Forest Grove, Scappoose, & Woodland.
  • Most of the metro area will NOT see heavy rain tonight or Friday morning
  • South of Portland, rain will be very light or even dry at times through Friday evening!
  • A warm southwest wind (a Chinook!) this evening through Friday morning brings gusts 30-40 mph in the valley and temperatures into the 50s
  • Cascade snow changes to light rain at times tonight and Friday at all ski resorts.  Avoid Friday skiing, although it may briefly dry out at times up there.
  • Steadier rain resumes in metro area Friday afternoon/night, but it’s unlikely we see any sort of widespread flooding from Portland south.

Local flooding is possible anywhere north & west of Portland tonight and Friday.   The NWS has a flood watch in effect which means flooding is possible.  This could be an event similar to February 12th when several inches fell in Banks, Vernonia, Scappoose, Kalama etc… but very light rain central/south/east metro.

For the weather geeks…

It was good to see models come together the past 24 hours.   I love this graphic; the integrated water vapor transport or IVT.  Shows where the “river” is aimed this evening at 7pm, 10pm, and again Friday at 10pm.

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The ECWMF is probably farthest north showing the intense rain band developing this evening to our north; hitting Centralia/Chehalis and Olympia with the biggest downpours.  Six hour rain ending at 10pm

ecmwf_6hr ending 10pm

Then 6 hours later ending at 4am Friday

ecmwf_6hrending4am

and 10am-4pm Friday

ecmwf_6hrending10am

The 24 hour total ending Friday afternoon shows very little rain south of Portland, just an inch in the city, but a solid 3-5″ up north

ecmwf_24hrfridaypm

GFS model is similar this morning although an even more stark cutoff to rain in metro area.  It pours in Forest Grove but sprinkles in Molalla

gfs_24hrfridaypm

And finally the GEM (Canadian)

canadian_24hrfridaypm

Of course if models are 50 miles off on placement, heavy rain could still show up in the metro area.  Good reason to keep the Flood Watch going!

What about Mt. Hood?  Is the meager snow pack going to wash away?  No, although we sure won’t gain much.  It’s very early in the season, but snow pack is running at less than 50% of average in much of northern Oregon

or_swepctnormal_update

Warmer air is surging into the Cascades right now and will push the snow level above 6,000′.  The bad news is that with the fire hose aimed north of Mt. Hood, snow levels stay high until early Saturday.  Anything that falls from this afternoon through Friday evening should be in the form of rain, not snow.  The good news?  The main band of rain is so far north that I don’t expect a dumping rain on Mt. Hood Friday, just light rain at times.  That said, a warm/humid airmass eats snow more quickly than any sunny 40 degree day in December.

Then as the whole system slides south and east Friday night, snow levels drop and we should see at least 6″ on the back side of this system.  Very tough to get additional terrain and/or ski areas open for Christmas Vacation without a good dumping.

79505643_3116397418387992_1665390409590767616_o

That’s it for now.  I’ll be at work all afternoon/evening.  We have lots of newscasts, you can catch us at 4, 5, 6, 8, 9, 10, or 11.

Chief Meteorologist Mark Nelsen


Weather Action Picks Up…For a Few Days

December 17, 2019

8pm Tuesday…

I’m still keeping a close eye on heavy rain expected on Friday.

An “atmospheric river” will set up late Wednesday through early Saturday along the West Coast.  An “AR” is a narrow channel of tremendous water vapor transport through the atmosphere.   From the tropics or subtropics into the middle latitudes (where we live).  For this reason they are often referred to as a Pineapple Express.  They can easily transport double the volume of the Amazon River overhead!  They have always existed, but the naming is relatively new (within the past 20 years).  You can read more about them on the AMS website.

Atmospheric River Rain Explain

I think the three day forecast summarizes things well:  light rain showers tomorrow, regular rain Thursday, then heavy rain Friday

3 Day Forecast Graphic Portland

Of course the big question is “will there be enough rain for flooding?”.  We still don’t know the answer; partly because models are trending DOWNWARD on rain totals now through Saturday.  First, widespread river flooding on the Willamette or Columbia river systems is very unlikely.  That’s because reservoirs are at their winter flood control minimum levels.  In fact Detroit Lake is 20 feet BELOW that level!  The entire storage system for the Willamette River is basically “empty” with respect to flood control capacity.

willamette

Unregulated smaller rivers are still at risk of course and then there’s the situation with “urban and small stream flooding”.  That happens when we get a long period of moderate rain or a few hours of intense rainfall.  The GFS model says forget about both.  But the ECMWF is still going gangbusters for a major rain event central/north/west metro Friday.  Check out 6 hour rainfall total just for 10am-4pm Friday centered right over the metro area

ecm_10am-4pmFri

It thinks we’ll see 3″ or so in a good part of the metro area in just 24 hours ending 10pm Friday night.  This would be a big deal and cause widespread flooding issues

ecm_24hrsending10pmfri

BUT, other models are somewhat/significantly drier.  Predicting exact location and intensity of atmospheric rivers is tough.  Models probably won’t settle down for another day or so.

To summarize:

  • We have a lot of rain on the way; definitely the wettest so far this season.
  • I’m confident we have at least two inches rain on the way for the metro area tomorrow through Saturday morning
  • We could see far more than that, but still don’t know yet
  • If you live in a location that has seen flooding during heavy rains in the past, pay close attention to the forecast
  • IF we get some flooding, it will be Friday or very early Saturday.  Don’t worry about tomorrow or Thursday.

Another item of interest; we go right back into split flow and upper-level ridging for Christmas week.  This isn’t a turn toward a typical wintertime wet weather pattern.  Just a blip in an unremarkable wet season so far.

Chief Meteorologist Mark Nelsen

 


Dry Early Week; Then LOTS of Rain

December 15, 2019

7pm Sunday…

Today sure felt like December…we only reached 44 in Portland under mainly cloudy (but dry!) skies.  That’s about normal for this time of year but the coolest day in two weeks.

These next three weeks are (on average) the coldest of the year in Portland.  The average high temperature is just 45 degrees from December 14th through January 5th.  It goes uphill after that time; reaching 49 by the end of January.  Our “winter” occurs earlier than other parts of the USA.  The darkest/coldest time of the year is right around the solstice.  I’ve always found it interesting that in our climate we go from summer to winter much more quickly than the reverse.  Springs are LONG here but we cool down quickly from late summer to December.

What’s ahead?  Two dry days for most of the region Monday and Tuesday; that’s due to high pressure temporarily overhead

ecm_tuesdaypm

But then for about three days we’ll be under the influence of a strong jet stream coming at us from the southwest.  This chart shows windspeed up around 18,000′ late Thursday night.  Notice the strong jet aimed right at the Pacific Northwest.

gfs_500_friam

And an “atmospheric river” is transporting a tremendous surge of moisture from the tropics into our area.  Precipitable water map for Thursday evening shows values up around 1.00″ or so.  I’ve seen higher, but this is the “juiciest” setup so far this wet season.

gfs_precipwater_Thursdayevening

Models are all showing several surges of rain from Wednesday night through Saturday.  Each is a bit different, but notice the operational versions of the GFS/GEM/ECMWF all give a huge soaking to the northern half of western Oregon and southern part of western Washington.  Click on each for a closer view of rain forecast now through next Sunday.

So the million dollar question is whether this will just be a “very wet period” or will this be a flooding setup for some of us late in the week?  We don’t know yet, but we’re watching it closely.  Check a couple of model “ensemble forecasts”.  Both say that SOME PART of the region will get a lot of rain.  The ECMWF ensembles show widespread 2-4″ in valleys and more in the Coast Range by midday Saturday.

ecmwf_ensemble_precip_saturday

The GEFS ensembles are interesting because they are running as a separate model now from the operational model GFS-FV3.  It was upgraded this summer, but the ensembles continue to use the old model.  In this case they are both showing the same heavy rainfall.

gfs-ensemble-all-precipsaturday

To summarize, confidence is high that we’ll make up a lot of our November/December rainfall deficit in just 3-4 days later this week. 

We could easily see 2-4″ rain in the valleys; luckily reservoirs are at the lowest of winter and creeks/rivers are very low.

I’ll keep a close eye on it this week; otherwise enjoy the dry weather these next two days.

WHAT ABOUT CHRISTMAS SNOW?

I’m still seeing nothing for the lowlands the next 7-10 days.  We dry out around Sunday and then turn cool & drier heading deeper into Christmas Week.  It’s the same splitty upper-level flow we’ve been seeing since around Halloween.  As of now I don’t see a single model showing anything close to lowland snow through Christmas Eve or Day.  Check out the 51 ECMWF ensemble members.  Only 3 of 51 produce some sort of lowland snow between now and Sunday the 29th.   Sorry kids!

ecmwf-ensemble-KPDX-indiv_snow_24-6411200


No Sign of Lowland Snow Next 10 Days

December 10, 2019

9:30pm Tuesday…

These first 10 days of December have been mild; quite a turnaround from that cold Thanksgiving week.

web_PDXTemp_13days

Of course we’ve been on the dry side since early October too.  Both Oregon/Washington saw a dry fall.  Take a look at the precipitation percent of normal for the past 60 days

anomimage

I do see three wet days ahead.  A Pacific system moves inland tomorrow afternoon followed by lots of post-frontal showers in the colder airmass Thursday and Friday.  There are hints we could see vigorous showers Thursday with maybe hail or thunder.  Then I see another somewhat “splitty” jet stream setup this weekend and part of next week.  That’s a return to weak systems.  You can see the upper-level system heading into California on Tuesday

gfs_tuesday

All models advertise strong southwesterly flow of some sort later NEXT week (about 10 days out).  The GFS 500 millibar heights and anomaly for Friday the 20th…

gfs_fri20th

What I don’t see, at least during the next 10 days, is any setup for lowland snow or a freeze.  I’m sure not going to bother putting on my snow tires for now.  Maybe next week.

Snow levels will vary between 2,000-6,000′ in the next 10 days.  Probably lowest this weekend.  Notice not a single one of 51 ECMWF ensemble members produces snow in Portland through Christmas Eve either!  Leading up to the Thanksgiving cold spell there were multiple ensemble members hinting that we might see some snow fun.  But you see nothing here.

ecmwf-ensemble-KPDX-indiv_snow_24-5979200

I’ve also been noticing the consistency in those ensembles for 850mb temps (temp in Celsius around 4,000′) through the next two weeks.  Not a single member down below -6; that’s when I start getting interested in lowland snow setups.

tseries_850t_000-360_Portland

The last time we saw snow in December was Christmas Eve 2017.  You may remember a couple hours of light snow, followed by a bunch of freezing rain.  It was a “Silver Christmas Morning” in 2017.

December Snow PDX 2017

To summarize

  1. There’s no sign of lowland snow or a hard freeze in the next 10 days, possibly longer
  2. That means we’ll make it at least 2/3rds of the way through December without snow
  3. We can’t see much beyond that point, although there are no hints of anything a little farther out.  It’s too early to know if we’ll be close to snow or ice for Christmas Week

Chief Meteorologist Mark Nelsen