A Beautiful Weekend; Showers Return Tuesday

October 15, 2017

9:30pm Sunday

The weekend is pretty much over now but wasn’t that fantastic for October?  Both days were mostly sunny with a chilly start (more so Saturday) and nice afternoons.  By the way, the 36 at PDX Saturday morning was the coldest temperature we have seen in the first half of October in a generation!  October 15th 1992 we hit 33 degrees.  Today was obviously warmer…high temperatures peaked in the mid-upper 60s in the metro area.

High Temp Last 13 Days

It’s always funny how quickly things change from late September to late October.  Just 2-3 weeks ago we were thinking high temperatures in the 60s were chilly, yet I think most of us would agree today was a spectacular day.  We have one more beautiful day tomorrow and then we get into a mild & wetter pattern.  This October has been totally different from last year.  At this point last year we had received 5″ of rain and almost no sunshine.  This year we’re seeing piles more sunshine.  In fact if we were cloudy EVERY DAY after tomorrow the rest of the month, that would just give us our average number of cloudy days…

Mark Cloudy Days Summer

 

The jet stream is setting up to our north much of this week with Oregon on the mild side of that jet.  That means snow levels will remain high until Friday and we won’t see any heavy rain in most of our viewing area.  Check out RPM forecast of rain the next 2.5 days and you see very little falls south of the Columbia River in the interior of Oregon

RPM Precipitation Accumulation

Yet by the end of the week, a 2nd atmospheric river event will likely trigger some flooding across NW Washington and SW British Columbia just to our north:

ECMWF Precipitation Accumulation

With the warm airmass overhead, we can expect mainly rain in the Cascades until a cold front comes through Thursday night or Friday morning

ECMWF Snow Level From 850mb Temps

Most likely 5-8″ new snow will fall at Timberline and possibly as low as Government Camp Friday and/or early Saturday.  That’s after quite a bit of melting during the workweek.  I think it’s unlikely we’ll see a re-opening of that Pucci chairlift at Timberline again this weekend.  That was amazing to see 27″ snow on the ground down below 6,000′ the past few days.  A nice change from our warmer Octobers.

Enjoy the sunshine Monday!

Chief Meteorologist Mark Nelsen

 

 


EF-0 Tornado Today In Aurora

October 12, 2017

10:30pm Thursday

Well that was an exciting afternoon!  We started with a steady soaking rain this morning, then went into a sunbreaks/showers pattern the rest of the day.  As expected a few thunderstorms popped up along with the usual hail, downpours, and breezy wind.  Now remember yesterday we had numerous funnel clouds/waterspouts off the coastline and up in Puget Sound.  Today some of that spinning energy decided to touch down in the Willamette Valley.

This was a weak tornado, even by Pacific Northwest standards.  It was weaker than the Lacomb tornado last month.  But it still flipped two planes at the Aurora Airport and damaged a bunch of greenhouses nearby.

This is also the only tornado I’ve seen pass close to an official observing site.  Check out the observations from the ASOS sensor near the southern end of the airport:

A couple of things to notice.  First check out the wind shift.  From gusty southerly just as the twister passed by, yet you can see how localized wind is with tornadoes.  Then notice the peak wind gust was only around 30 mph at the sensor which is maybe 1/2 mile south of the tornado path.

This will rank on the low end of tornadoes around here.

I missed all the excitement because I had the day off.  I was taking a run up the road with no cell service from 3:45 to 4:30.  Came back to a whole bunch of texts and warnings.  But with all this weather fun I had to come in of course.  That’s one benefit of your hobby becoming a career.  It’s all the same to me.

Looking ahead, we still have a nice and dry weekend, the rain returns Tuesday.  Enjoy the briefly dry weather!

Chief Meteorologist Mark Nelsen


First Snow in The Passes This Week

October 10, 2017

7:30pm Tuesday

After 5 months of warmer than normal temperatures the month of October has been much different.  We are only 10 days into the month and we’re running well below normal.  In fact with the clouds and rain arriving just after midday, we ended up 7 degrees below average for the date.  A cold front is passing through the region right now, the leading edge of a much cooler airmass.  This begins a 3 day period of showers in the valleys.  Of course just like last month we’ll likely see a few thundershowers at times along with hail too.  But this time the airmass is colder which equals lots of Cascade snow!  That’s one reason I quickly finished up work in my garden the last two days, planted garlic, shallots, & cover crop.  I think we’re done with the warm season!

Take a look at the ECMWF model forecast of snow level over the next 6 days

The snow level (lowest elevation we expect snow to stick) should linger around 4,000′ through Friday night, then quickly rise well above all ski areas Saturday through at least next Monday.  With several disturbances giving us waves of showers, the snow is going to be piling up relatively deep up around 5,000′ and above.  Here’s our forecast for snow totals plus Cascade driving conditions

Yep, I think we could see up to 2 feet of snow at Timberline, and possibly up around 10″ or so down at Government Camp…that’s spread over the next 3 days.  Of course in October snow levels go up and down so most or all of that will melt this weekend and early next week.  But this should be the earliest measurable snow at Govy we’ve seen since October 2009; quite a change after the past few years

There will also be some snow (just a bit) over some parts of the High Desert of central and eastern Oregon…most likely Thursday and/or Friday.  Plus the first snow of the season could fall in the Wallowa Valley…winter is getting closer

Looking farther ahead, a strong “zonal” flow sets up Sunday through much of next week.  That means a Pacific jet stream will consolidated and flow mainly west to east, instead of this north/northwest flow bringing us the chilly showers right now.  Now typically that’s a very wet pattern for us in Fall.  But in this case Sunday and Monday the jet will be to our north, then sag south over us Tuesday through the rest of next week.  The result is a nice dry spell centered right over this weekend…good timing.  Note the ECMWF ensemble 24 hour precip forecast for the next 10 days:

You see not a single ensemble member has rain over us during that period, but they all are quite wet NEXT Wednesday-Friday.  Pretty good agreement the middle/end of next week will be a soaker.

To summarize

  • The next 3 days will be cool & showery in the lowlands and snowy above 4,000′ in the mountains
  • Cascade passes will be snowy at times the next 3 days, although only the summits will be icy since the snow level doesn’t go much below the passes….you’ll run into snow only near the summits
  • Saturday through Monday = dry, with varying amounts of morning fog to afternoon sunshine each day
  • Tuesday & beyond next week = back to wet weather

Enjoy the showers…everything is back to normal in the Pacific Northwest!

Chief Meteorologist Mark Nelsen

 

 


Eagle Creek Fire Soil Burn Maps

October 5, 2017

I’ll be talking about these maps on the evening newscasts but want to get it online as well.  The Eagle Creek Fire “Burn Area Emergency Response Team” has released a survey of fire impacts to the vegetation & soil in the Gorge.  The results are contained in a large map here:

https://l.facebook.com/l.php?u=https%3A%2F%2Finciweb.nwcg.gov%2Fphotos%2FORCGF%2F2017-09-03-1149-Eagle-Creek%2Fpicts%2F2017_10_04-19.43.14.983-CDT.pdf&h=ATMJmwV2jVpdGd8TiW3PevreLdUCKxuxI4jCIsYbGnN5h2I148RpG8CUVy1-Neu5_OzkSMn1eeFHAnv-TjvPd9_aPrZw5VzWoHRvt0dhBFDg3OtZbzsGxSb3YovqAZbqul5C-hn_

I’ve zoomed in on several areas so you can take a close look at your favorite hiking destinations or routes.  Of course you would probably like a legend to go with the map…

Fire Eagle Creek Soil Damage Explain

This from the BAER folks:

High burn severity is indicated by the burning of all or nearly all of the ground cover and surface organic matter (leaves, needles, and decaying plant matter), including fine roots. Moderate burn severity has consumption of up to 80% of the ground cover. In areas with low burn severity, much of the organic matter on the surface is not fully burned and roots are generally intact.

The higher the burn severity is, the less likely the soil is able to absorb water from rainfall and snow melt. Severely damaged soils will produce more and faster water runoff. They are also more prone to erosion and landslides

 

Fire Eagle Creek Soil Damage Maps

Fire Eagle Creek Soil Damage Maps2

Fire Eagle Creek Soil Damage Maps3

Fire Eagle Creek Soil Damage Maps4

I notice a few things…real intense burn around Franklin Ridge & Oneonta Gorge.  But much of the far western edge of the fire was in the low to very low category otherwise.  But check out the red throughout the Tanner & Eagle Creek canyons.  That’s pretty bad and in that area the fire moved many miles south of the Gorge.  Once you get to the eastern end of the fire from Herman Creek to Mt. Defiance the intensity was lower again.  This may be because this area burned last, just before the heavy rain finished off the fire.  Temperatures were a bit cooler and westerly wind generally brings a bit higher humidity; that can possibly reduce fire intensity.

I took a drive through the Gorge (as far as Cascade Locks) last weekend and again yesterday.  After seeing video of the fire on the 4th and 5th one would think there would be almost nothing left.  That is most definitely not the case.  It looks the same as it did before; just a little…different.  I’ve got 3 observations for you:

1) Lots of burned brush below mainly green fir trees…this is a common sight.  Some of that tree bark is black a good 20 feet up.  That will be a reminder of the fire for a few decades to come.  In these areas new greenery will pop up by next April/May.

2) On many of the high ridges you can see burned trees without the needles so the forest up there looks a little “thin”.

3) Nowhere did I see a totally bare landscape, except the upper part of Angel’s Rest with just a few “toothpick” trees sticking up.  Remember that’s one spot that burned over in the 1991 Falls Fire too.  Once the trail opens up there will be even more views to appreciate.

Chief Meteorologist Mark Nelsen


A Beautiful Start to October

October 3, 2017

6pm Tuesday

It’s only the 3rd of October, but we’ve already seen more sunny days than ALL OF LAST OCTOBER.  Today is considered a “clear” day and last year we didn’t have a single clear day.  Remember October 2016?  The rainy season began a month early last year.  Lots of clouds…

And of course it was a big soaker as the jet stream ramped up early.  Last October was the 2nd wettest on record in Portland

In a typical October here, the first half (or more) of the month is reasonable; occasional weak weather systems mix with sunny/dry periods.  But last year the rainy pattern began in earnest immediately.  My neighbor told me it was the last straw…he sold his house and moved to the Desert Southwest this past summer.  He should have stayed one more year because the first 10 days of this month still look fantastic.  That’s due to high pressure in the upper-atmosphere wanting to linger nearby or just to our west.  You see the current IR satellite image with the stable “high over low” pattern along the West Coast.  That means the jet stream is going well north, then swinging south around the high and then low. This pattern also gives us a nice & warm offshore flow regime at the surface.

 

That gave us the warm temperatures in the lower 70s this afternoon.  Expect a few degrees warming the next 3 days.  Now Saturday and Sunday (sorry about the weekend timing) the high breaks down with a strong WNW jet stream just to our north.  That pattern will bring in a very thick marine layer plus lifting.  TranslationExpect a very gray and cool day Saturday with a good chance of drizzle or light showers.  That will linger in the mountains through SundayResultThis weekend will NOT be warm & sunny.

But then high pressure develops right over us again for a quick return to offshore flow and sunshine next Monday.  This shows up nicely in the ECMWF relative humidity cross-section.  I’ve circled the weekend.  Thick saturated airmass up to Timberline Lodge or so = gray days.

The 2nd period of warm and mainly sunny weather may last a good chunk of the 2nd week of October.  Yes, it’s possible most of the first half of October will dry and pleasant!

The ECMWF ensemble 24-hr precipitation chart shows that 2nd dry period, then quite a bit of “noise” from the 13th onward.  That’s because the basic pattern appears to change after the first two weeks of the month.  The ECMWF/GEM/GFS models all show upper-level troughing (low pressure) developing in the Eastern Pacific for the 3rd week of October

And here is the corresponding weekly precipitation anomaly (drier than normal is brownish) for NEXT WEEK

Then the 3rd week of the month…looks like wetter westerly flow may come back after this two-week period of mainly dry weather.

By the way, we will be close to the frost point in only the coldest outlying areas west of the Cascades tonight.  I think 99% of us westside will remain frost-free for at least the next week though, and that’s not unusual.  Most areas west of the Cascades don’t get a first frost until the 2nd half of the month or even early November.

Enjoy the sunshine!

Chief Meteorologist Mark Nelsen


4th Wettest “Water Year”

October 1, 2017

9pm Sunday

October is here and that means we have just wrapped up a “Water Year”.  So what is THAT?

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 and snowmelt 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 one 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?

This last rainy season was VERY wet.  51.45″ in Portland and of course far more in the mountains.  We typically get around 36-37″ precipitation in the city each year so we gained a solid 15″ more rain than what we’d typically see

This season was the 4th wettest, behind 1996-1997, 1995-1996, & 1955-1956.  The highest on record was 58.67″.  The flooding in February, November, and a bit at the end of December pushed that year into the #1 spot.

Of course last year was a weak “La Nina” year so we expected higher than normal rain, but not THAT much rain!  It’s interesting that the dead of winter (December/January) was drier than normal due to the cold weather.  If we’re down around freezing we’re not getting the usual mild/wet systems coming through.

Snowfall in the Cascades ended up well above average up above 4,000′ and near average at pass elevations.  It’s about what we’d expect in a weak La Nina winter, although note Government Camp just barely reached a “normal” year.  The reason the ski season was so great down low was because the dead of winter was colder than normal and the good snow hit right away in late November and December.

We’ve got lots of sunshine ahead the next few days…this October is looking FAR different from last year’s washout.  We only had 3 dry days the entire month last year plus ZERO clear days.  We’ll easily exceed both of those stats in this first week of the month.

Chief Meteorologist Mark Nelsen

 


Goodbye to 80 Degree Days

September 28, 2017

6pm Thursday

Today we hit 86 in Portland, the 2nd consecutive day we’ve reached well into the 80s

As expected the onshore flow…well, flowed onshore quickly this afternoon at the beaches.  Check out mid-afternoon temps vs. highs yesterday (in red) on the Oregon Coast

Today was the 79th day at/above 80 this warm season in Portland.  That’s the 3rd greatest number of 80 degree days we’ve seen (chart doesn’t count today)

As I’ve mentioned regularly, our summers have been warming somewhat dramatically the past 30-40 years.

Portland averages about 15 more days above 80 than back in the mid-20th century.  That’s great if you live in the foothills or mountains in the summer, but not so great if you live down in one of our cities near sea-level (inland).    I’m bringing up the “80 degree chat” because I think it’s unlikely we hit 80 again this season.  Of course it’s POSSIBLE we hit 80 for the next 3 weeks, but unlikely

Models are showing a normal to below normal temperature weather pattern for the next week or two.  The upper-level pattern is not very wet, with ridging in the Gulf of Alaska.  But we remain on the cool side of that ridge.  Note the Tuesday, then NEXT Saturday GEFS (GFS ensembles) chart:

Then the ECMWF showing a weaker ridge, but same general pattern in its week 2 ensemble.  This is the average of all 7-14 day maps

A few thoughts on the next 10+ days based on this:

  1. With weak systems coming over the ridge and even some split-flow at times, this will be a real pain forecasting showery periods
  2. But the next two weeks won’t feature a stormy & wet pattern in the Pacific Northwest, in fact most likely it’ll be a little drier than normal
  3. Cooler and drier air coming down from the north should give us sunny days at times (middle of next week)
  4. Drier air also means much cooler nights.  Those typical chilly October nights are on the way by next Tuesday…way down into the 40s in urban Portland and 30s outlying areas
  5. Hitting 80 in Portland again appears unlikely, although if the ridge edges closer with offshore flow it COULD happen again.

Showers arrive tomorrow midday and expect more light showers Saturday & Sunday.  ECMWF says less than 1/2″ rain the next 3 days, then we go dry after Monday.  That’s good, I can avoid watering the garden once again…

 

Chief Meteorologist Mark Nelsen