Snow Thoughts

March 5, 2009

Snapshot I've looked at maps pretty closely this evening and have a few thoughts about possible snow this weekend.  There isn't much happening in the next 48 hours…just a partly cloudy day tomorrow and then a sharp cold front Saturday.  There has been one surprise tonight; the snow level has dipped to 1,000' in a persistent line of showers centered on Highway 26 from Sandy east to Zigzag.  Looks like all of the Hoodland area is getting at least a dusting.

Okay, now on to Saturday night and Sunday.  First…this is not like 1951.  As I mentioned yesterday, the upper level low was far deeper back then and 850mb temps were significantly colder.  So I sure don't see those 8" of snow at PDX.  Here are my thoughts:

1.  The chance for low elevation snow (let's say below 500') is late Saturday night and Sunday morning before 10am.  Then late Sunday night too if moisture keeps coming in.

2.  IF we get some good precipitation during the correct times, any area could get significant snow (1"+).  But the pattern looks pretty showery to me.  I do notice that there is more moisture forecast with this period than what we saw last Thursday.

3.  Those of you (us) at/above 1,000' are going to see several inches of snow (maybe up to 4" or so?) again.  Ugh! It would be nice to work outside this weekend now that March is here, but apparently that won't be the case. 

4.  WRF-GFS says no good sticking snow at the appropriate times in the lowest elevations, but WRF-NAM does.  Our RPM model says nothing through Sunday afternoon in the city.  I'll trust the GFS and our RPM for now considering how well they have done this winter.  But it's still not time to forecast amounts yet…I've got another 24 hours for that.

5.  Forecast Temps:  I see some of you think our highs in the 40s are too warm for the cold airmass coming in.  Drew and I are assuming there will be some sunbreaks and at least some brief periods of decent clearing between showers Sunday.  That's how we get 43.  Keep in mind that the extremely cold atmosphere the last week of March last spring saw us get to 46-50 when we had a dusting of snow on the ground in the morning.

The Tuesday night pattern sure grabs my attention as well.  On the GFS, a system approaches from the west while cold and dry air is pulled down into the Columbia Basin.  That gives us a classic set up for a snow storm in winter, and maybe some snow in March too.  Depends on the track of the offshore system, how much moisture comes in, and how cold the air is eastside.

This all adds up to an interesting weather period for us to watch from late Saturday through the first few days of next week.  Thankfully that appears to be it for cold weather with warmer temps coming up Wednesday-Friday of next week…Mark Nelsen