Tuesday Morning Update

February 28, 2012

We still don’t expect sticking snow TODAY here in the western Valleys…it’s just a little too warm.  Take a look at our morning RPM model prediction of snowfall from 4am today to 4am Wednesday.

If anything, I think it’s a little underdone for the heavier snow showers coming in later tonight and the Wednesday morning commute.  This map would imply no snow even up on the West Hills, Mt. Scott, Bald Peak etc.  As mentioned in yesterday evening’s post, I think ANYONE could see a brief dusting early Wednesday morning, but a trace-3″ is sure possible near and above 1,000′ by tomorrow morning.

In the short term, one band of showers has raced well ahead of the main rain band (still offshore), and with it’s early arrival we could easily see snow mixed in with the rain as we continue to gradually warm up.  10am temps say it’s already too warm to stick; up around 37-40 at all the official observing sites.  Plus, I see a milder south wind arriving right now in some of the hills like Mt. Scott and the West Hills.  Good news if you DON’T want snow.

The forecast for increasing afternoon rain still looks good, but Wednesday morning should be snowy, at least in the air, for most of us.

Chief Meteorologist Mark Nelsen

Snow Arriving In Coast Range

February 28, 2012

Looks like the first band of precipitation is falling as snow in the Coast Range this morning.  So the snowy weather is beginning up there and will continue through Thursday.  It may just turn to rain, especially at these lower spots, from this afternoon through early this evening.  But then all snow after that tonight and most of tomorrow. 

Here are the two ODOT cameras from Lees Camp along Highway 6 and Murphy Hill on Highway 18:

Chief Meteorologist Mark Nelsen

ECMWF Weekly Maps

February 27, 2012

As I mentioned in today’s previous posting, wide variability in the 5-10 day forecasts, but for fun, here are the 30 day ECMWF maps from last night’s run.  This operational run has ridging over or nearby from early next week over the following two weeks, then back to cool troughing for…Oregon’s Spring Break.  There’s your 30 day outlook right there…






February 27, 2012

I think I can smell a slow-roasting “forecast bust” as I come into the weather kitchen this evening.  The slow cooker will be working overtime tonight and tomorrow morning…

The National Weather Service and at least one or maybe two other forecasters in town (as of the early evening shows) are calling for at least some sticking snow tomorrow evening down here in the lowest elevations in the city.  I think that’s very unlikely; my reasoning is below. 

Here are the highlights:

1. Rain arrives in the metro area and north Willamette Valley around midday tomorrow, sometime between noon and 2pm.  It should fall as rain with snowflakes POSSIBLY mixed in just about anywhere.  Temperatures peak around 40 and stay there all the way through late tomorrow evening.  I don’t expect a temperature drop back down towards freezing.

2. I don’t expect sticking snowfall anywhere in the metro area; the only POSSIBLE exception could be out around Banks and Vernonia if temps don’t warm too much.  Other than that area; up against the east slopes of the Coast Range, you’ll need to be up around 2,000′ to find sticking snow tomorrow afternoon.  Even the central and eastern Columbia Gorge looks very marginal for snowfall late tomorrow afternoon; I-84 will probably be slushy at worst.

3.  Starting late tomorrow night through Thursday, we’re back in the cold showers and clearing periods pattern; almost exactly what we saw over the weekend.  That means each morning any of us could see snow mixed in with the rain, but sticking snow Wednesday and Thursday morning will probably stay in the hills, closer to 1,000′.

4.  Put this together, and you can see we still don’t see a return to winter (lots of snow or a deep freeze) here in the lowlands of western Oregon or SW Washington.  Just more of the late winter cold showers that occasionally mix with snow.

Now, on to the technical chit-chat:

I wasn’t scheduled to work today, but after seeing the snow talk ramping up, I figured I should work and take some other boring weather day off.  Plus, we have NASCAR on right now so no early shows and plenty of time to check out all the other sources of weather information.   Clearly I had too much spare time today…

We have two separate forecast “snow issues” in the next 3 days.

A. Pre-Frontal steady precipitation from midday tomorrow through tomorrow evening.

This doesn’t look nearly cold enough for snow to me; it doesn’t even look that marginal compared to some past events.  In fact if the NWS Discussion hadn’t mentioned it this morning, I would have just said “40 degree rain” and not even mentioned the snow possibility for tomorrow:

1.  Surface temps are too warm and models don’t show the usual “evaporative cooling dip” when we have a dry airmass and moisture starts moving in (December 29, 2009).

Note the 4km WRF-GFS Meteogram  and our RPM  text output for 1-10pm tomorrow:

2. No mesoscale model shows snow accumulating at the lowest elevations

3. Significant warm advection to a bit above freezing in the 1,000-3,000′ layer.  Note the 1.3km WRF  cross-section.  Not only is the 0 degree (celsius) line heading towards 850mb, but the +5 line lifts above the surface!  That goes along with the meteogram above and our RPM text data above showing we hang right around 40 from midday tomorrow through late evening.

4. No cold and dry air coming through the Gorge to keep chilly air in place.  All I really need to say is “1-2 millibars easterly flow tomorrow and it was 46 degrees at The Dalles today”.

5.  In deference to the “Forest Grove Effect” with an approaching low pressure system and slightly cooler air banking up against the Coast Range, I said we could get some stickage out in places like Banks and Vernonia, but I’m not to encouraged that even that will happen.

B. Cold Post-Frontal Showers late Tomorrow Night through Thursday

This is pretty much the same as what we just went through this past weekend.  The old “showers and clearing periods” pattern.  Most of us at the lowest elevations saw nothing. 

I should say that I am somewhat impressed by Wednesday morning’s precipitation intensity.  This looks similar to what brought us lower than expected snow levels on Saturday morning.  In fact our RPM shows all of 0.3″ snow over Portland at that time (around 7am Wednesday). 

So THIS period appears to be the best chance for snow showers to lower elevations.  The Wednesday morning commute will probably bring some heavy snow showers for all of us, but still, anything other than a brief dusting will remain above the lowest elevations with afternoon temps up into the lower 40s.

If you live in the hills up around 1,000′ or higher, 1-3″ is likely again Wednesday morning and again 1-2″ Wednesday night and Thursday morning.   Shower intensity really backs off Wednesday night too, we saw what happened Sunday morning compared to Saturday, even fewer spots saw a dusting for that reason.  Lots of snow covered roads (again!) for Wednesday and Thursday mornings in the hills.

If you live 1,500′ or higher?  Could be sticking snow anytime after 10pm tomorrow night through Thursday evening, with most of the accumulation Wednesday.  6-10″ at that elevation easily.  Here is the 3 day snowfall forecast  from our RPM model. 

Beyond Thursday, upper level ridging moves overhead through the weekend for significantly warmer 850mb temps, so seasonal March highs in the 50-55 degree range will return.

Here are the 12z GFS  and 12z ECMWF  850mb ensemble charts…huge disagreement on either warmer ridging or more cool troughs in the next 10-14 days.  Look at those lines all over the place, especially on the ECMWF!  We’ll see which way it goes.

Chief Meteorologist Mark Nelsen

Morning Update: Sunday 8:15am

February 26, 2012

If you were hoping for that TRACE of snow on the lawn this morning, you were likely disappointed.  Lots of cloud cover overnight kept temps from dropping and little or no shower activity.  I didn’t think it would be quite that dry.  Either way, forecastwise it worked out just fine.

Sticking snow level appears to be around 1,000′ or so at 8am (it’s wet at my home at that elevation) and should generally stay within 500′ of that the rest of the day; so no sledding this afternoon in the lowest elevations (no big surprise!).  Radar has been filling in the past couple of hours.   Mesoscale models do show more moisture through the rest of the day for lots of cloud cover and off/on showers.  They just don’t appear to be the heavy convective showers we saw yesterday.  The WRF-GFS shows lots of action across Clark County, so you may be able to score an inch or two from Battle Ground north and east?

Skies clear  out this evening and overnight as high pressure settles in and cooler/drier air filters in from the north.

Monday still looks perfectly sunny…a good time for a day off (me).

A change for Tuesday…the moisture is going to be arriving slightly later, midday at the earliest.  That plus not much easterly flow coming through the Gorge and increasing southerly wind with a low farther north spells the end of snow possibilities for the lowest elevations in the afternoon.  Maybe something up against the Coast Range or above 1,500′ but that’s it.  Even getting snow in the Gorge could be tough since temps will warm all day ahead of the precipitation which arrives late afternoon there.

As mentioned in an earlier posting, chilly showers Wednesday and Thursday, but not quite as cold as what we saw yesterday, so no snow to the lowest elevations there either.  Hopefully this will be the last time we need to discuss snow in the lowest elevations this late Winter/early Spring.

Saturday Evening Update: 4:15pm

February 25, 2012

Here are the graphics I’m using for the evening show…I’m working tonight since I was already scheduled, not due to “SNOWPOCALYPSE 2012: THE REBIRTH” coverage.  I’m just kidding, we don’t have crazy out-of-control weather coverage tonight.  But some good pictures from the Cascades and Coast Range.

Today worked out pretty well, temps were within a few degrees of 40 most of the day; officially a high of 44 so far at PDX.  The showers were quite intense this morning, but there is a weakening trend since around 2pm on the radar.  Most likely we’ll see about half of the radar echoes disappear with the loss of daytime “heating” after 6pm too.  

Take a look at precipitation forecasts for Portland from several models, these are from 4am Sunday through Sunday evening when it dries out:

12z NAM: .07″
12z RPM: .08″
18z RPM: .04″
12z GFS: .09″
18z GFS: .05-.18″ depending on whether you use TTD or PDX.

If you want snow in the lowlands, that’s the main weather factor working against you the next 24 hours.  For this reason, I scaled back the snow totals even in the hills as you see in the graphics above.  I would be surprised to see more than a trace of snow officially out at the Portland forecast office.

Monday should be a great day with sunshine the entire day due to cool and dry air filtering in from the north.  Not an arctic blast, but a late February chill in the air.

 Tuesday is still really up in the air forecast wise.  If we get solid precipitation rushing in here quickly in the morning, we could see snow in the air everywhere and sticking even in some spots.  If it comes in slowly (like 11am or later) or is very light with a splitting trough, just a cold rain.  Something to keep an eye on.

If we don’t get anything on Tuesday, most likely we are done with a chance for sticking snow at the lowest elevations for the year.  Wednesday has onshore flow type showers like today except the airmass isn’t as cold, then slightly warmer temps later in the week with no real cold troughs (-6 or below at 850mb) showing up in the long range maps.

Chief Meteorologist Mark Nelsen

Quick Morning Update

February 25, 2012

Everything proceeding according to plan, although heavier than expected precipitation brought the sticking snow level a little lower than I would have thought.  Still lots of heavy showers passing through the rest of the day, but now most sticking will be well above 1,000′ and partially melt between those showers.  Mine is slowly melting here at 1,000′.

All the rest of the forecast info on the previous post still applies, so I won’t rehash it until this afternoon when I’m at work.

850mb temp was -6.5 deg over Salem this morning and with heavy showers that was enough to bring sticking snow well down into the hills.  The air mass temp cools maybe 2 more degrees in the next 24 hours.

Two things I notice on maps/models this morning:

1.  Lighter or very little precipitation after sunset this evening all through tomorrow; could be less snow at/above 1,000′ then we saw this morning?  Check out the 2 different 24 hour snowfall forecasts from the WRF-GFS and our own RPM.  I’m really surprised our 4km RPM shows nothing over the higher hills in the Valley.  This tells me it’s a lack of precipitation and not an issue of “is it cold enough”.

2.  Tuesday morning is going to be a close call here in Portland.  It could be a significant late season wet snowstorm in the central/eastern Gorge.

And for fun, here’s the 12z GFS ensemble 850mb chart:


Chief Meteorologist Mark Nelsen