A Chilly End To February Ahead; Snow For Some

February 19, 2017

9pm Sunday…

Have you noticed the snowflakes in the 7 Day Forecast here at FOX12 or on your weather app?  I’ve got the scoop…

First, We will not be having a snowstorm this week in the lowest elevations of western Oregon or most of SW Washington.  But we should ALL see snowflakes in the air or even and SOME of us will get some snow on the ground.  I don’t think you’ll see me snowblowing a foot of snow in Salmon Creek again:

snow

That said…later this week we’ll be in a weather situation where many of us will see snowflakes.  But this time we won’t have a cold east wind blowing out of the Gorge or a cold air mass to give us a widespread snowstorm.  
Instead we get light showers and clearing periods Wednesday through Friday; it happens to be a colder version of the “showers and sunbreaks” pattern we often see in the winter and spring.  We’ve seen this pattern only two other times this winter…back in early December (it kicked off the fun stuff on the 5th) and on February 6th.  In both of those situations little or nothing fell in the very lowest elevations along I-5.  That includes much of the metro area.  That’s because often in this setup we get a breezy southerly wind coming in off the 50 degree Pacific Ocean, keeping the lowest elevations just a few notches above freezing.  Not always, but maybe 90% of the time.

We can’t predict the sticking snow elevation (the “SNOW LEVEL”) well in these “snow shower” patterns like we have later this week either.  No matter how often someone tells you it’s going to snow down to 750′, or 500′, or 250’…forget that nonsense…I generally stick to 1,000′ increments in these situations nowadays.  That’s because (for example) heavy showers in one location could drag the snow level down to 300′, yet just light showers 10 miles away don’t drop snow at 1,000′!  I’ve seen that happen many times.

In general, the higher up you live the better chance you have for sticking snow later this week.  Cooler nighttime air, by just a couple of degrees, for Wednesday night and Thursday night means a better chance for sticking snow down below 1,000′.  That’s assuming showers keep going all night as well.  That’s why I think the best window for a dusting down in the lowest elevations is the late night and early morning hours Wednesday night through Friday AM.  Of course as we get closer we’ll refine the forecast and give you more detail…as always.

You can see the general idea just by checking out the ECMWF snow forecast through Saturday:

ecmwf_snowthrusat

See the big empty hole here in the valleys?  And as we saw back on February 6th, models often overdo the lowest elevation snowfall in these marginal setups.  Check out the Cascade snowfall!  It looks like some of the best this season with very low snow levels from Wednesday until further notice

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Here’s the ECMWF ensemble chart from this morning’s run.

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That’s the next two weeks, time goes from left (right now) to right.  Green line is average 850mb temperature for the date (temperature at 4,000′ in celsius), the blue is the operational run and red is average of all the ensemble runs.  This screams a very chilly last week of February and first week of March.  To get sticking snow with onshore flow this time of year we need -7 to -9 at 850mb.  Notice we’re very close to that several times in the next two weeks.  Of course if we lose that onshore flow and get decently heavy showers at some point, it could snow/stick all the way to sea level even as warm as -3 or -4.  So the main message here is that we’ll be flirting with snow in the lowlands several times in the next 2 weeks.  Anything is possible so let’s get the wishcast express loaded up folks!

WishcastingExpress

Chief Meteorologist Mark Nelsen


Are We Done With Winter?

February 15, 2017

10pm Wednesday…

It’s only February 15th, but this is the time of year folks often ask me if we’re “done with winter”.  If you have lived west of the Cascades for long, you know that yes, in general we don’t get big winter weather events after mid February (snow/ice/flooding).  I don’t think I’ve seen significant freezing rain, flooding, or day-long snowstorms after about February 20th while working here in Portland.  That goes all the way back to 1991!  BUT, that doesn’t mean it can’t happen.

marksnow_poll

Lots of you took the poll in the past few days (previous post).  Looks like a majority of you think we’re either totally done with snow or we’ll only see a little in the hills.  63% of you say that there will not be any more measurable snow at the lowest elevations here in the city.  History says you are most likely right.  Take a look at what we’ve seen AFTER FEBRUARY 20TH in Portland during the past “generation”.  That’s considered to be 25 years.

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Yes, we’ve only seen measurable snow (that late in the season) 4 out of those 25 years.  So the odds are very much against additional snow.  Keep in mind this is at the official observing location out at the Parkrose NWS.  Obviously if you live at any elevation above that you know we’ve seen 1, 2, or even 4″ during some of those events!  Remember March 2012?  Quite a few inches in mid-March that year, plus coastal and valley snow.  But that was the exception.  In March Portland has seen measurable snow in only 4 of the past 50!

There is a tendency to see late season cold events or late season snow in La Nina winters, which we are now in.  So it would be quite premature to pull out the fork at this point and declare winter over.  That said, I’m quite confident we’re well past the worst winter has to offer.  Don’t take the studded snow tires off quite yet…give it another couple of weeks.

By the way, February has been a big soaker, about 3 times our typical rainfall so far:

rainfall-so-far-this-month_compared-to-normal-or-prev-records

It’s the wettest February since I was just 30 years old…a long time ago.  More rain coming…

Chief Meteorologist Mark Nelsen

 


Poll: Are We Done With Snow in Portland?

February 13, 2017

The past few days have definitely given the feeling that “the worst of winter is over”.  This happens every February in our mild climate; you’ve probably noticed this if you’ve lived here for awhile.

I can tell you that it’s extremely rare to get freezing rain in the Portland metro area after mid-February.  In fact during the 26 years I’ve been forecasting here in PDX, I’ve never seen freezing rain after Valentine’s Day anywhere in the metro area.  I have seen it maybe twice or three times in the western Gorge in early March, but even that is quite rare.  So we’re done with the ice threat in the lowlands west of the Cascades.

But snow?  What do you think…are we done with it in Portland this year?  Let’s vote:

I’ll give you my thoughts on possible snow the rest of the season on Wednesday.

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Two Nice Days Ahead, Then Wet

February 12, 2017

11pm Sunday…

A very slow weather night and mainly slow week ahead as we creep through the final stretch of winter west of the Cascades.

High pressure has settled overhead, giving us another dry day.  East wind has that “end of winter” feel too, not nearly as strong as what we have seen in December and January.   Even the temperature chart shows the last 4 days of 50+ weather are the longest stretch since around Thanksgiving…winter is losing it’s bite!

marktemp_last13days

Tomorrow’s high temps will be around 50 in the metro area under mostly sunny skies, same thing for Valentine’s Day too.

The rain is definitely coming back though, that’ll be Wednesday night and Thursday as a southwesterly flow sits over us for about 36 hours.  This won’t be a flooding event like the last one, I expect less than 2″ in the lowlands during that time.  You can see the precipitation forecast numbers from both the GFS & ECMWF are similar:

One final note; a hiker turned up missing this afternoon while hiking just west of Multnomah Falls.  Almost all those trails are still in “winter mode” which means tons of snow/ice/downed trees across them and most are shaded from the sun until those higher sun angles of March.  Remember that out in the Gorge it has been cooler with the last ice storm occurring less than a week ago!  This is the one year every generation where you shouldn’t be hiking in the Gorge until we get a widespread melt in March.  It’s not a good idea to attempt hiking through the snowiest/iciest conditions we’ve seen in the Gorge in 30+ years.  Give it time to melt…

Chief Meteorologist Mark Nelsen

 


Ice Storm in Gorge, But 60 in Valley!

February 8, 2017

11pm Wednesday…

Quite a contrast across the region as cold air is slowly receding at the lowest elevations from the Portland area through the Gorge and into Eastern Washington.  Meanwhile warm air has moved in aloft with 40s at the ski resorts.   At the same time southerly wind is pushing 60 degree air up through western Oregon.

current-temps-orwa-plot

Strong wind will continue along the coast, but those gusts in the 60-65 mph range won’t cause much damage, that’s normal out there in winter.  Heavy rain is falling through the Coast Range too and as the cold front moves through the metro area at sunrise we’ll see some real downpours here too.

So hang on, by midday tomorrow the heavy rain will be finished and temperatures will ever so slowly rise above freezing in the Gorge.

Until that time I expect another 1-1.50″ rain west of the Cascades and a solid 1-1.50″ ice in the Gorge.  This is another big ice storm out there and hopefully the last of the season!

By the way, with temperatures pushing 60 tomorrow as the south wind arrives in Portland, that’ll make it the warmest day since November!  Enjoy…

Chief Meteorologist Mark Nelsen


Ice Storm #5 in Gorge, Cold Rain Metro Area Wednesday

February 7, 2017

10pm Tuesday…

A very wet frontal system arrives over the Pacific Northwest tomorrow morning, with the heaviest rain moving through tomorrow night and very early Thursday morning.  For most of us it’ll be just rain west of the Cascades.  But once again cold air is getting dragged back into the central/eastern Gorge (the part of it east of the Cascade Crest) due to an approaching storm out in the Pacific.  In other places this is called “cold-air damming” and that’s what is really going on; cold air is dammed up east of the Cascades.  This time the airmass isn’t as cold as previous events, so even in the western Gorge (west of Bonneville Dam) the airmass will be marginally cold for freezing rain.  Regardless, an Ice Storm Warning is up for very heavy 30-32 degree rain Wednesday AM  through Thursday morning.  A lot of ice can form on objects even at just 30-31 degrees, especially when the sun goes down.  Believe it or not, this is the 5th ice storm we have seen in the western Gorge!  Wow, typically I’ve only seen 1/2″ or more every other year on average.  It’s not too unusual to have freezing rain 5 times in one winter, but not actual ice storms with the heavy accumulation.  Total ice thickness could exceed 1″ this time again.
markwarnings_freezingrain_metroplusgorge

Once you get into the Central & Eastern Gorge (Cascade Locks to The Dalles) the cold air is deeper to start with so precip type will be snow…maybe 3-6″, then as the cold air thins tomorrow evening it should go to freezing rain out there too.

markwarnings_freezingrain_metroplusgorge2

There won’t be any real warming west wind on Thursday to get the cold air out of the Gorge, but the gradually warming airmass should go above freezing that day.

Will there be freezing rain in the metro area?

I don’t think so…it probably won’t get cold enough even at Troutdale.  Just expect a very wet day tomorrow.

There IS a  flood watch out for all areas west of the Cascades due to about 2″ rain expected tomorrow morning through Thursday afternoon.  Expect more isolated areas of flooding tomorrow night and early Thursday.  Plus a few larger rivers may reach flood stage again.

These first 7 days of February have been the 3rd wettest start in Portland’s weather history.  The number will sure climb with another 2″ on the way!

rainfall-so-far-this-month_compared-to-normal-or-prev-records

Chief Meteorologist Mark Nelsen

 

 


Surprise Snow For Some This Morning

February 7, 2017

11am…

The snowy system moving through Southern Oregon today spun moisture much farther north than expected, right over the Portland metro area this morning!  Luckily with the cloud cover just about all of us were above freezing the past few hours, but lots of us in the east metro area are seeing snow in the air.  Temperatures are staying cool because a chilly east wind returned through the Gorge overnight.

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It appears the band is beginning to fall apart a bit, although the HRRR says some light precip will continue the rest of the day.

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I have almost 2″ here at 1,000′ in the Corbett area.  So much for that morning run…bust!

At this point with the easterly flow diminishing the rest of the day (not much new cold air coming west), the chance of widespread sticking snow for 90% of the metro area is quite small.  But those hills in the east metro could see sticking snow off/on the rest of the day!

The National Weather Service hasn’t issued any warnings/watches for the ice & snow storm coming in the Gorge tonight & tomorrow.  It turns out they HAVE issued watches/warnings but they aren’t showing up on the main page that collects all the warnings here:  http://www.wrh.noaa.gov/warnings.php?wfo=pqr

But I’ll be blogging about that later today.

Chief Meteorologist Mark Nelsen