Widespread Snow Likely Tuesday Evening & Night

February 19, 2018

2:00pm Monday…

Last night the clouds didn’t clear out as expected so we just dropped to freezing or a bit below in the metro area.  Lots of icy streets but it appears it wasn’t a total ice-pocalypse for the morning commute.

Today we’re under a dry flow of air from the north which is giving us lots of sunshine but chilly temps…a good 10 degrees below average.  We’ll end up around 40 or so.

We have an almost perfect sticking snow setup for the lowlands with two disturbances coming straight down from the north the next 3 days.  They pick up a bit of moisture once they move over the coastal waters offshore, then generate snowfall in mainly Western Oregon and SW Washington.  The one issue (if you want lots of snow) is that it’s late February and daytime heating is “strong” for late winter.   This DOES keep us from having an all-day snow/ice event where roads stay frozen…you know, continuous-coverage type snow event for TV folks.  Roads just don’t stay frozen/icy the whole day this time of year…whew!

I see two good chances for lowland snow before a slight warm up Friday night and into the weekend lifts sticking snow levels back up into the foothills.  1st is tomorrow afternoon through early Wednesday morning, the 2nd is early Thursday morning.

We have a big problem forecasting how much snow we get tomorrow afternoon through early Wednesday…models have widely varying snow totals and also put the heavier stuff in different places.  Check out 7 different models showing total snow accumulation by 4am Wednesday.  Blue on most of them is 2″ (or more). See the issue?  You can click on each individually for a larger view.

The big message here is that SOME AREAS BETWEEN OLYMPIA AND EUGENE SHOULD GET A GOOD 2″ OR MORE SNOWFALL BY WEDNESDAY AM.  But SOME AREAS WILL ONLY GET A DUSTING TO 1/2″.  Each model is slightly different in the placement of precipitation.  Note the one that shows 4-6″ snow centered on metro area.

If this was all rain none of you would notice; we’d just forecast increasing rain showers Tuesday afternoon through Tuesday night.  Would any of us care if we got .05″ rain instead of .30″?  Nope!  We wouldn’t even notice, it would just be a little wet.  But when that falls in the form of snow that’s the difference between a dusting and 3″!  Suddenly it matters!  You see the forecast problem now don’t you?

But I get paid to make a forecast and prepare you for the possibilities, so here’s what I’m thinking this afternoon:

  1. Light snow showers develop most areas west of the Cascades tomorrow afternoon, then pick up in intensity after 6pm or so.
  2. Temperatures likely hover near/above freezing through early evening, so MOST LIKELY roads will be mainly wet through the evening commute.
  3. Dropping temps and increasing snowfall should turn many roads snowy by late evening.  No, we don’t know exactly when; it depends on snow intensity and how warm it gets during the daytime.
  4. Expect 1/2″ to 3″ in the western lowlands from Longview to Eugene.
  5. Many roads/areas will have fresh snow on the ground for Wednesday AM commute, then thaw during the day (travel just fine during day).  Wednesday may be a Snow Day for many areas west of the Cascades.

 

COULD TUESDAY EVENING’S COMMUTE TURN INTO A HELLISH EVENING WITH TRUCKS & CARS STUCK ON FREEWAYS…LIKE LAST WINTER?

YES,  That is a “worst-case” scenario at this point, not likely but possible.  If snow starts falling heavily during the evening commute, temps could immediately drop to 32 degrees and we could have a fiasco.  How to avoid?

  • EVERYONE should have chains, studded tires, and/or 4 wheel drive vehicle available for use tomorrow evening just in case this happens.  Otherwise please don’t get on roads/highways if they turn snowy.
  • Hopefully transportation agencies have learned quite a bit from last year.  For example I would hope salt is in place to keep interchanges, ramps, & bridges clear this time.  (personal opinion ahead)… The de-icer used in the past doesn’t seem to do much; in both storms last year highways just froze up.  Why do we soak our highways in thousands of gallons of chemical if it freezes anyway? …(end opinion) Remember some of you stuck at I-84/I-5 interchange for 6 hours?  Same on approaches to Marquam Bridge and Sylvan Hill.  Bad memories we don’t need to repeat…

 

WHAT ABOUT SCHOOLS TOMORROW?

With a little daytime heating I think we’re fine until sunset in most lowland locations.  But administrators should be keeping a close eye on noon/early PM temperatures and radar.  I’ll be doing the same.

COAST?

Snow showers all day tomorrow.  Not much stickage since temps will be above freezing, but after dark maybe a little on roads.  I could see a Trace to 1″ anywhere along the coastline, with more in the Coast Range of course.

GORGE?

Same as western lowlands, although drier in the eastern Gorge, farther removed from moisture.

That’s the update for now, of course I’ll be keeping a close eye on things in case for some reason timing suddenly speeds up (morning snow!) or models turn much heavier with the snowfall.

Good times ahead!

Chief Meteorologist Mark Nelsen


Snow Ends, Cold Night Ahead

February 18, 2018

11:45pm…

Did we say ZERO to 1/2″ in the lowest elevations?  Well it ended up as ZERO to 3″ in the lowest elevations of the metro area and Willamette Valley.  Quite a wide variety of snow totals…here’s the final snow map, I’ll add in a few numbers tomorrow.

Snow Totals Metro Area

That disturbance really dumped the heavier stuff on the eastside and then up into Clark County.  West and south metro were left out again.  Salem had nothing, except in the hills.  So in reality most of the western valleys of Oregon had very little.

So officially at the NWS office we now have two measurable snowfalls this season (Christmas Eve and Presidents Day “Eve”), plus one Trace (Valentine’s Day).  Nice holiday lineup.  What’s coming on St. Patrick’s Day?

Enjoy the bright sunshine tomorrow and drive carefully the next 10 hours as roads freeze up.

Chief Meteorologist Mark Nelsen


9pm Update: Widespread Snow East Metro

February 18, 2018

Well, it never works out EXACTLY as planned with snow around here.  Everything was looking good until about 6pm.

A few models had shown a last surge of snow showers this evening and they were right!  A little disturbance is rotating directly over the metro area, seen nicely in radar the past 3 hours.  It started out over Battle Ground, swung south over East Portland, and now appears to be shearing off to the west as easterly flow has begun blowing over the Cascades and through the Gorge.  This easterly flow SHOULD dry out the showers the next few hours, I sure don’t expect a repeat of 1-4″ snow turning to 2-18″ like January 2017.

But it is pretty clear that NOTHING TO 1/2″ will turn into NOTHING TO 3″.

I’m on the air on FOX12 PLUS right now (Channel 49, 13 on cable), and I’ll be on FOX12 from 10 to 11:30pm.

Here are the snow totals so far, feel free to add yours in the comments below

Snow Totals Metro Area


Nice Snow Globe Effect Today

February 18, 2018

 

 

10am Sunday

Some heavy snow showers are rolling through NW Oregon and SW Washington this morning.  When they hit it looks like your neighborhood briefly inside a snow globe doesn’t it?

Our forecast has been working out perfectly so far (surprise!) with most lowland locations getting either nothing, or just a light dusting.  Coolest temps have been west and north metro and that’s still the case at 10am:

web_metrotemps

That southerly breeze is still going which is almost always a snow-killer at the very lowest elevations:

web_wind_ORWA

Quick look at ODOT and WADOT cameras shows most areas bare at 9am, and all roads clear in the lowlands too

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The forecast remains the same today…we can just chop off the morning part:

NOW THROUGH 6PM

– Snow showers continue, lots of sunbreaks too.  In fact it may be just partly cloudy the entire 2nd half of the day for many of us.

NEAR/ABOVE 1,000′  Some light accumulation at times since temps remain closer to freezing up there.  Slushy or wet roads up there

LOWER ELEVATIONS  Wet or dry roads, snow in the air at times…we top out in the lower 40s

THIS EVENING AFTER 6 PM

– Light snow showers could stick anywhere and then eventually end.  If you get lucky, a heavy shower could pass right over your neighborhood and you get a quick inch!  This happened during a very similar weather pattern January 1st, LAST YEAR.  A line of heavy showers dropped up to 2″ snow from Canby over to Molalla while most of us got nothing or just a dusting.

TOTAL SNOW BY THE TIME IT DRIES OUT TONIGHT?

  • NOTHING TO 1/2″ Most likely for lowest elevations of Western OR & Clark County
  • TRACE-1″ more likely Kalama to Longview (slightly “wetter” up there)
  • 1-3″ near/above 1,000′

***  I’ll be on the air 5-6 PM on FOX12, then 8-10PM on FOX12 PLUS (the old PDX-TV 49 or 13 on cable), then 10-11:30PM on FOX12.  Lots of newscasts on weekends now too! ***

MONDAY AM

– Dry skies, frozen ground/streets.  If no snow falls in your neighborhood this evening, then it’ll just be scattered icy spots for AM commute.

REST OF MONDAY  Roads dry out, chilly and mainly sunny

 

TECHNICAL INFO:

Nice surface low is spinning down through Western Washington right now and will pass right over or just north of the metro area by early afternoon.  I have a feeling someone will get lucky in the metro area and see a quick dump of 1-2″ snow under a heavy shower band…sometime between now and when it dries out this evening.  But of course I don’t know where.

Late tonight through Tuesday midday is an easy forecast…cold & dry.  850mb temperature forecasts have been consistent showing at least a -11 deg. at 850mb during the daytime tomorrow.  As usual, the NAM is on the cold side, but GFS and ECMWF have been more reasonable.  Getting to -10 or below is somewhat rare, even in winter here.  In fact if the Salem sounding site gets down to -11, that might be the coldest in a few years.  I don’t recall that happening last winter, most of that cold air was low-level for each of those events.

12z models (haven’t seen ECMWF yet) have backed off a little on possible widespread snow Tuesday night in NW Oregon and SW Washington.  The ECMWF and GEM went full-on snow event for Tuesday night & Wednesday AM.  No warming southerly low-level wind and a dry airmass (for evaporational cooling)

web_ECMWF_Text96Hrs_00z

Note the 2-4″ snow in metro area followed by clearing and frozen conditions Wednesday AM!  Remember this is last night’s run.  That “BC Slider” forecast to come down the coastline is a bit farther offshore on the NAM/GFS this morning, while the morning GEM & ECMWF still sends snow over us.  I’ll be watching it closely!

See you on-the-air this evening!  Well, actually it’s a one-way thing.  You can see me but not the other direction.

Chief Meteorologist Mark Nelsen


Saturday Midnight Quick Post

February 17, 2018

11:45pm Saturday

The forecast from Thursday night still looks good!  Temperatures still have a ways to go before we can even think about sticking snow at the lower elevations.  11pm numbers:

web_metrotemps

 

Check the previous post for more detail, but here’s a fresh summary:

SUNDAY 6AM-10AM

– Snow showers in hills, could be a TRACE to 2″ anywhere at/above 1,000′  SOME SNOWY ROADS POSSIBLE UP THERE

– Snow showers in lowlands, but a few degrees above freezing.  So it will either be no sticking or a “barkdust/grass/cartop” sticking in spots.   WET ROADS

SUNDAY 10AM-6PM

– Light snow showers continue, lots of sunbreaks too.  In fact it may be just partly cloudy the entire 2nd half of the day for many of us.

– NEAR/ABOVE 1,000′  Some light accumulation at times since temps remain closer to freezing up there.  Slushy or wet roads by early afternoon up there

– LOWER ELEVATIONS  Wet or dry roads, snow in the air at times…we top out in the lower 40s

SUNDAY EVENING AFTER 6 PM

– Light snow showers may continue and then eventually end.  IF WE’RE GOING TO GET WIDESPREAD STICKING SNOW IN THE LOWLANDS THIS WILL BE THE TIME.  

TOTAL SNOW BY THE TIME IT DRIES OUT SUNDAY NIGHT?

  • NOTHING TO 1/2″ MOST LIKELY FOR THE LOWEST ELEVATIONS IN WESTERN OREGON. 
  • TRACE-1″ more likely Kalama to Longview (slightly “wetter” up there)
  • 1-3″ possible near/above 1,000′

 

MONDAY AM

– Dry skies, frozen ground/streets.  If no snow actually falls in lowlands Sunday evening/night, then it’ll just be scattered icy spots for AM commute.

REST OF MONDAY  Roads dry out, chilly and mainly sunny.

Models are converging on a possible 2nd snow event Tuesday night.  More on that tomorrow!  But the unusually cold weather plus more than one chance for lowland snow this upcoming week scared me enough to reschedule my vacation.  I’ll be taking a week off in spring instead of this coming week.  Seems more appropriate don’t you think?

Capture

Chief Meteorologist Mark Nelsen


Weekend Snow Possibilities & Cold Weather Next Week

February 15, 2018

5pm Thursday

The coldest airmass we’ve seen in late February since at least 2011 will be arriving Sunday night.  Now that we’re within 3 days of possible snow at the lowest elevations, it’s time to get into a bit more detail.

HIGHLIGHTS FOR WESTERN VALLEYS

  • There is no chance for lowland snow through Saturday night...we’ll have typical rain showers through this time.  In fact quite windy & mild Saturday (50-52 high)
  • During the daytime Sunday, the sticking snow level will hover in the metro area hills (close to 1,000′).  But we’re talking off/on snow showers.  Sunbreaks in-between combined with typical daytime heating keeps the “stickage” in the hills.  Showers will be light as well which helps.
  • Roads below 1,000′ should remain snow-free during the daytime Sunday
  • Sunday evening colder air rushes in, but it’s very dry air too.  Most likely snow showers change to light flurries and then end.  Temperatures drop below freezing all areas
  • Any water left on roads Sunday evening will freeze, plus some spots in the western valleys may see light snow accumulation on those roads.  There will be icy/snowy areas on some roads for the Monday AM commute but it may not be widespread
  • Total snow at the lowest elevations?  Could be NOTHING for many of us through this period…not a real wet pattern.  I’d be surprised to see much above 1/2″ in the city.  1-3″ more likely up above 1,000′ of course.

 

TO SUMMARIZE:  AT THIS TIME, I THINK “SLEDDABLE” SNOW IS UNLIKELY FOR MOST OF US IN THE LOWEST ELEVATIONS.  LESS THAN 1″ IS LIKELY FOR MOST

This graphic summarizes my snow thoughts:

Beyond Monday morning, the vast majority of our models keep us dry through Wednesday.  The airmass will be the coldest so far this season.  Very dry air combined with clear skies could drop most of us into the teens Monday night and/or Tuesday night.  But under bright and strengthening late February sunshine, afternoon highs should still make it close to 40 each day.  Think typical Central Oregon winter weather.

WHAT ABOUT COAST & GORGE?

COAST: Too warm during the daytime Sunday for sticking snow out there, but ZERO to 1/2″ would be my best guess for coastal towns Sunday evening and night.

GORGE:  We don’t have a cold easterly wind blowing in the Gorge, so not much different from westside.  A TRACE to 2″ is most likely Sunday evening through Monday AM.

 

TECHNICAL DETAILS

For a snow/cold event, models are in surprisingly good agreement through at least Monday.  All show the upper-level trough digging down right over us Sunday and Monday from the north.  The sequence of events sure looks like the November 2010 freeze.  The cold air just drops in from the north instead of coming at us through the Gorge.  850mb temps are in -6 to -8 range during the daytime Sunday, which this time of year should be (just barely!) enough to keep sticking snow off the valley floor.  If we had more vigorous showers forecast by models I would go for sticking in spots during the day.   Then they are all in good agreement drying things out quickly after 00z Sunday PM.  Folks this is a classic case of moisture disappearing right when the cold air arrives (like Nov 2010).  Note the 4pm Sunday to 4pm Monday precipitation forecasts from both WRF-GFS and ECMWF…almost nothing

And you see the snowfall forecast through Sunday 4pm…which seems a bit high even though it’s showing all of 1/2″ at most in the metro area.  Check out the Cascades!  Yep, this should be the best weekend of the entire winter up there!

How about the cold?  I’ve checked out the February 2006 and February 2011 late season cold snaps.  A few interesting points…one is that the cold airmass modifies quickly compared to midwinter events.  The other is that with full sunshine and weak Gorge wind, it’ll be easy to get highs up into the upper 30s.  Thus my forecast highs of 38 both Monday and Tuesday.  Both ECMWF and GFS bottom out 850mb temps around -11 to -12 over Portland on Monday.  That’s real cold for this time of year, although not record low.   It’s interesting that we’ve never made it down to -14 over Salem after the first few days of the month.  This is also not going to be a big east wind event for us, even Monday and Tuesday.

Later next week?  Since we have more cool troughs dropping in on us later in the week, the most likely scenario is a switch to onshore flow and rapid modification of the airmass.  That would lift snow levels above the valley floor in the 2nd half of the week.  That happened in 2006 and 2011…not much snow going out of the cold airmass since there is no Gorge wind to hold in the cold air.

I will be off for my weekend the next two days, but back in Sunday.  If there’s anything dramatically different from what I’ve posted above, I’ll update this blog on Saturday.  Otherwise you can assume nothing has changed.

Chief Meteorologist Mark Nelsen

 

 


Snow Returns; First Time in 7 Weeks

February 14, 2018

9:30am Wednesday

Well that was interesting.  I forecast snow based on computer modeling alone yesterday afternoon/evening.

Lets imagine we didn’t have any numerical simulations of the atmosphere (THE MODELS).  Looking at observations last night in our area, I would not have forecast snow.  It wasn’t cold enough.  For example at midnight I’m driving through Portland on the way home and temps were in the low 40s!  No cold Gorge wind blowing and cloudy skies so no nighttime cooling.  Dewpoints weren’t that low so evaporational cooling shouldn’t have been able to produce overnight snow at the lowest elevations. But models kept insisting the column of air overhead would cool…2-3 hours later IT DID! #ComputersTakingOver

IMG_3323

I had 2″ at 1,000′ east of Corbett. I know it was a trace accumulation or just in the air for the lowest elevations, but we expected that. If you got more than 1/2″ let me know in the comments below…we use the info for a snow map on-air.

Chief Meteorologist Mark Nelsen