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