Snow Totals: Big Mountain/Foothill Storm

February 28, 2011

If you have 1″ or more, please put your total in here.  Go ahead and keep updating totals through tomorrow morning.

1.  Total

2. Location

3. Elevation (within 500′ at least).

Big Snow Storm In Hills Today

February 28, 2011

Today we’ll see the best snow accumulation of the winter in the hills on the east side of the Metro area and into the Cascade Foothills.

A strong cold front passed overhead during the morning commute (notice the wind suddenly dropped off?) and now lies down in the Valley.  Just behind it it is cooler air with the freezing level down around 2,000′.  Normally you might expect snow just a little below that, but with the very heavy precipitation rates (.85″ @ PDX since 4am!), the snow level drags all the way down to near sea level.  Sticking snow appears to be falling to around 500′, especially onthe eastside of the Metro area where the precipitation is heaviest.  I already have 2″ at home.  It appears that the dropping snow level has bottomed out with temps holding steady the last hour or so.  If you don’t have snow now in the metro area you probably won’t get it. 

This will continue all the way through tomorrow morning as the front becomes almost stationary over Northwest Oregon.  Combine the great atmospheric forcing with a stationary front and you have a tremendous snowstorm that’s just getting going.  Heavy snow has begun falling in the Cascades and will continue through Tuesday morning…imagine a total of 2-3′ in just 24 hours!   Our RPM model forecast for the next 18 hours is down below.  When you read maps like this one, don’t get too hung up on exact location of contour lines.  The graphic is “machine-made”, so it interpolates between points.  It knows 30″ at the crest of the Cascades and nothing in Portland, and generally sees a “smoothed” elevation map.  But it can’t account for every ridge and valley.  For example, it isn’t going to snow 10″ at Multnomah Falls at sea level with a west wind, but a graphics program can’t handle that kind of detail for drawing the contours.  More importan is that  this is a 4km model.  That means the grid points are 4km across…wider than the Gorge.  It sees the Gorge as a low pass.  All models do that to one degree or another, depending on their resolution.

Down in the lower elevations, I expect the sticking snow level to climb a bit to 1,000′ or even a little higher by this afternoon, but it won’t go above 1,500′.  So how much snow in places like Sandy, Detroit, or the hills above Washougal, Corbett, and Estacada?  There’s no reason a foot of snow couldn’t fall in those areas, but at least 6″.  This happened one day in February 2008 when I got 9″ at 1,000′ at home and it was significantly deeper just 500′ higher, but none in Portland.   This setup also tends to give power outages with the falling trees in the Hoodland area from Sandy to Rhododendron. 

Beyond that, a quick jump in freezing levels tomorrow afternoon ends the snow threat at the lowest elevations.  The big windstorm for Wednesday is a bit farther offshore, so just windy here in the Valleys with strong wind at the Coast.

Chief Meteorologist Mark Nelsen

Flurries Tonight

February 26, 2011

Today we tied the coldest temp of the winter in Portland…18 this morning, and only have seen a high (so far) of 33 degrees.  That was also a record low MAXIMUM temperature for the date.  I also believe (but don’t have the numbers), that was the first time we’ve seen lows in the teens beyond Valentines Day since 1989…extremely rare.   That first March day in the 60s is going to feel REAL GOOD this year isn’t it?

A quick post because I’m actually taking a day off.  Some “snizzle” out there this afternoon and evening, mainly east Metro areas.  Sounds like light sleet (clinky), but also light snow too.

Models are doing real well as of 10pm.  Extremely limited moisture, and temps holding steady (or even rising in a few spots).  Dewpoints in some spots are gradually rising as well.  That should be the trend the rest of the night.  Temps hold between 32-35 in the lowest elevations, with an increasing chance for flurries towards the morning.  We’ll probably wake up with a dusting on the ground, but roads should only have a dusting too, or be just wet.  Soon after sunrise the increasing southwest wind will warm all areas below 1,500′ above freezing.  So still not a big snow event; I think the NWS is probably playing it safe with the Winter Weather Advisory…which is fine of course.  But it may be hard to get that 1″ due to the lack of moisture.  Our RPM has no signficant moisture (more than a few hundreths) until midday. 

Of course one thing models did terrible on was the cloud cover today…almost totally cloudy after 10am.  That kept high temps right around freezing.   In fact it’s kind of cool (meteorologically) that Hood River and The Dalles have had a gusty WEST wind, but temps still below freezing!  That’s because the usual warmer air source (west of the Cascades) is still real chilly.   Basically we’ve got a lot of cold/dry arctic air to moisten up the next 12 hours…but it’ll gradually occur.

A note to the “commenters”.  I’ve had several emails the last 24 hours about some “bullying” in the comments.  I don’t want to see that on here.  Whether it’s on video or text…don’t be harassing other weather geeks.  Each person has something to contribute (even Brian and his cold GFS numbers!), so I won’t tolerate one group picking on a single person.  And, unrelated, but apparently it needs to be repeated…don’t Drink and Blog!  Especially cross-continent.

Chief Meteorologist Mark Nelsen

Lots of Exciting Weather Ahead

February 25, 2011

The coldest night of the winter for many of us westside is in progress right now.  Yes, some places were colder earlier in the winter, but it’ll be close.  Still waiting for the north wind in the Valley and east wind in the Gorge to completely decouple from the surface.  With dewpoints around 10 many areas, it should be easy to get down into the teens.

So we’ve got moisture moving in tomorrow night, cold air in place, and a perfect setup for a brief snowfall?  That forecast above is the 72 hour period ending Monday afternoon.  Note it shows possibly a dusting (spotty) in the Valley.  Possibly, but I see two things working against it (and mesoscale models seem to agree) getting more than a dusting:

1. Moisture is very slow to move in and quite light from late Saturday evening through daybreak Sunday…just a few hundreths of an inch.  Not the best if you want really good evaporational cooling.  That moisture dropping into the cold air and evaporating, thus taking “heat” out of the airmass.  Temps cool as that occurs.

2. Onshore flow commences by sunset tomorrow, picking up, and by Sunday morning we’ll have a breezy southwest wind blowing up the Valley and THROUGH the Gorge too.  Not a real warm airmass, but should be enough to lift the snow level up to 1,000′ or so.

Once we get past that, the threat for widespread snow in the LOWEST elevations is over, but it’ll be close off/on through the next 7 Days.  If you think of a late-winter La Nina weather pattern, this would be it.  Many feet of snow in the Cascades and even down into the foothills through the first week of March.  Models show 2-3ft. of snow just from Sunday midday through Monday afternoon!  It’s unusually cool westerly flow through the whole 7-10 day period.  Looks like Monday night the snow level is back down around 1,000′ again (briefly).

Chief Meteorologist Mark Nelsen

Snow Cover on Satellite

February 25, 2011

This is a great (but huge) image from the Terra satellite taken late this morning.  Look closely, you can see the leftover snow in southern Clark County, and even leftovers from the swath of showers that went through SW-NE Portland yesterday.  And of course the heavy snow from Woodland to Longview shows up real nicely.  Click on it (several times) for a REALLY large view!

Cold Air Moving In

February 24, 2011

Real calm weatherwise this evening…the calm after the “storm” I suppose.

Cold and dry now as the last flurries seem to be just about gone on radar and east wind is picking up across the Metro area.  Our dewpoint just dropped about 5 degrees in the last hour at the station.  We’re freezing up nicely across the region as the modified arctic airmass moves in.  The low dewpoints will help dry out roads, so I don’t expect a major huge mess for the morning commute; just areas of ice and some leftover snow on the hills or shady spots. 

I’m really looking forward to the sunshine the next two days.  Though it’ll be chilly (and breezy tomorrow), it’ll be nice to be blinded by the bright late February sun.  Speaking of calming wind, perfect radiational cooling should drop us to right around 20 tomorrow night.  No snow cover to help for most of us after another sunny day in the 30s, but it’ll still be unusually cold for this late in the season.

I’m keeping an eye on the transition into wet weather…appears to be Saturday evening or night as precipitation arrives.  Good chance of a snow start with real nice evaporational cooling, but southwest wind picking up during the night means it can’t last that long.  There is not dry/cold air coming in from the east at that point.  In those situations it’s usually not a significant snow event.  I also notice the precipiation amounts are quite light for the first 12 hours; that doesn’t help if you want snow either.  The main message is that it doesn’t look real exciting right now, we should wake up to rain on Sunday morning.  At best rain with some leftover snow melting on the ground.

I’m also keeping a close eye on a deep low forecast to move north up the coastline late next Tuesday.  The last two runs of the GFS have been impressive, especially the latest at 00z.

In general, as March begins, we’re heading into classic La Nina early spring conditions; cool and wet.

Here are the snow total maps from today…click for a better view.  Notice how Clark County had more than the top of the West Hills!

Stay warm!

Chief Meteorologist Mark Nelsen

Midday Break, Then Evening Flurries/Freeze

February 24, 2011

The official total from the overnight/morning snow at the National Weather Service Forecast Office was a huge….0.7″  For those math-challenged, that’s about 3/4″.   Still the biggest snow of winter season…on February 24th!  And that total may rise this evening…maybe.

BUT, we have a Snow Totals posting here on the blog plus Facebook and it’s clear that official total was the low end.  Generally the inner/eastern part of the city had less than 1″.  But lots of SW, W, E, and Clark County had 1-3″ (almost everywhere else).

BETWEEN NOW & LATE AFTERNOON:  Pretty quiet.  Late winter sunbreaks, temps up around 35-37, plus just a few scattered snow showers means good driving conditions. 

THIS EVENING:  Could get messy again for two reasons:  Cold air moving through the Gorge will spread into the Metro area, freezing everything up at some point after dark.  EVERYTHING will freeze in all areas.  At the same time our models show a possible burst of snow showers.  So another Trace-1″ is possible during this time anywhere.

TONIGHT:  Hard freeze, but clearing skies…25  This means roads will be icy for GDO Friday AM, but blue skies.  Another snow day or two hour delay for lots of schools.

FRIDAY-SATURDAY:  Mostly sunny, but chilly…35-40 degree highs.


The above note is what I just sent out to our newsroom folks.  Looks like another long day today with real sparse showers and sunbreaks keeping temps above freezing at least through 4-5pm.  The good news is that the south wind is gone, gradients are now flat in the Valleys and easterly through the Columbia River Gorge.  I see the dry arctic air is moving through the Gorge this morning, and the WRF-GFS plus our RPM both show it arriving by 4pm at Troutdale and spreading through the entire Metro Area soon after dark.  That’s at the surface; above there will still be the last of the showers rotating through our region.  Models seem so be hinting (WRF-GFS and our RPM) that the colder air arriving below will give us one last lift to the showers.  So I’ll say another Trace to 1″ anywhere around sunset or just beyond before the moisture runs out.  Otherwise little/no accumulation during the daylight hours with those forecast highs around 37.

Chief Meteorologist Mark Nelsen