Close to Snow Today

February 18, 2011

I just mentioned to Julie Grauert “you know we were only 5 degrees from a surprise snowfall today”.  Of course she said “aren’t we often 5 degrees from snow (this time of year)?”.  Good point, but I suppose it’s more like 10 degrees.  It’s all about how low the snow goes from November through March.  In the case of today the moisture that models showed staying over and west of the Coast Range made it all the way to the foothills of the Cascades.  I was dry at my home east of Gresham until about 1pm; so you didn’t have to go far east to get out of the rain.  Some western sections of the Metro area had almost .30!  Same down in Salem.  High temps were in the 40-45 degree range; but the top of the West Hills (1,000′) in the precipitation remained 34-36 degrees all day.  The point of this is that we could have easily seen a “surprise” snowstorm…and probably would have if today was early January.

The surface low is sliding down the coastline and will be out of the picture by morning, giving us nice, dry, north and northeast flow.  A very nice Saturday with lots of sunshine.  Then it’s on to another system sliding down the coastline later Sunday and early Monday.  Models are mostly doing the same thing with that system, keeping almost all moisture (or all) offshore.  Considering models were about 50 miles off on the precipitation today, we’ll have to keep a close eye and see if we really do stay dry during that period.

Beyond that the “Elephant in the Weather Blog” is the looming arctic blast for next week.   My confidence in a big blast is definitely not high right now due to differences in model runs and the simple fact that were talking about an arctic front moving through the area 144 hours from this evening (late Wednesday or Wednesday night).  That is 5+ days away.   There IS lots of cold onshore flow ahead of the dry arctic air Tuesday and Wednesday.  This is another setup for snow to pretty low elevations; hills and foothills may get plenty of snow those two days.  IF wet get a nice surface low to develop in Wednesday or early Thursday along with a deep upper trough, we COULD see significant snow in the lowlands.  One way to phrase the issue would be this; everything has to line up just right in our climate to get snow in mid-winter, to get significant snow the last week of February though? Everything has to line up perfectly.  In the last 15 years, we’ve only had 3 measurable snowfalls in Portland in late February or March.  Less than 1″ each time.  Feb 2009, March 2009, and March 2006.  That shows everything has to line up just right.  The best would be a strong upper level low just over us or south, allowing surface wind to turn northerly or easterly (cold air) while a batch of snow showers slides in from the southwest from the upper-low.

I do like how all models are pretty cold for Thursday-Friday next week (ECMWF not exceptionally so).  So let’s pretend we get a big blast with 510-515 dm thicknesses and 850mb temps of -13 (coldest model I’ve seen).  How cold would high temps be under mostly sunny skies?  I think mid-February 2006 is a good example.  Arctic blast came in from the northeast, lowest 850mb temp at SLE was -10.3 degrees and -22.1 at GEG.  We had one daytime high around 32 at PDX the day the cold air moved in (with sunshine).  The next day it was 40.  IF we were to take the coldest model mentioned above, push it back 1 week towards Spring, we could see highs only in the low-mid 30s for a day or two.  We didn’t do that in our 7 Day forecast since that’s the coldest models show and the ECMWF would be more like 40-45 degrees.  Overnight lows could easily be well down into the 20s.  Record low maximums for the 24th-25th at PDX are 38-40 and record low minimums are 20-25 degrees.

I am more or less getting “kicked out of work” this evening.  I still sound rough but feel perfectly normal.  Unfortunately television is not just about how I look, but is also an audio medium.  So the boss said something like “why are you here?” a few hours after I showed up.  So I’m headed home after getting lots done: forecasts, emails cleaned up, schedules published, graphics made, etc…  I’ll have the pleasure of watching the 00z models come in like everyone else; from the comfort of home.

Chief Meteorologist Mark Nelsen